Online monitoring of transepithelial electrical resistance (TEER) in an apparatus for combined dissolution and permeation testing

RGD-coated polymeric microbubbles promote ultrasound-mediated drug delivery in an inflamed endothelium-pericyte co-culture model of the blood-brain barrier

Drug delivery to central nervous pathologies is compromised by the blood-brain barrier (BBB). A clinically explored strategy to promote drug delivery across the BBB is sonopermeation, which relies on the combined use of ultrasound (US) and microbubbles (MB) to induce temporally and spatially controlled opening of the BBB. We developed an advanced in vitro BBB model to study the impact of sonopermeation on the delivery of the prototypic polymeric drug carrier pHPMA as a larger molecule and the small molecule antiviral drug ribavirin. This was done under standard and under inflammatory conditions, employing both untargeted and RGD peptide-coated MB. The BBB model is based on human cerebral capillary endothelial cells and human placental pericytes, which are co-cultivated in transwell inserts and which present with proper transendothelial electrical resistance (TEER). Sonopermeation induced a significant decrease in TEER values and facilitated the trans-BBB delivery of fluorescently labeled pHPMA (Atto488-pHPMA). To study drug delivery under inflamed endothelial conditions, which are typical for e.g. tumors, neurodegenerative diseases and CNS infections, tumor necrosis factor (TNF) was employed to induce inflammation in the BBB model. RGD-coated MB bound to and permeabilized the inflamed endothelium-pericyte co-culture model, and potently improved Atto488-pHPMA and ribavirin delivery. Taken together, our work combines in vitro BBB bioengineering with MB-mediated drug delivery enhancement, thereby providing a framework for future studies on optimization of US-mediated drug delivery to the brain.

Development and Evaluation of EDTA-Treated Rabbits for Bioavailability Study of Chelating Drugs Using Levofloxacin, Ciprofloxacin, Hemiacetal Ester Prodrugs, and Tetracycline

Laboratory rabbits are fed foods rich with cationic metals, and while fasting cannot empty gastric contents because of their coprophagic habits. This implies that, in rabbits, the oral bioavailability of chelating drugs could be modulated by the slow gastric emptying rates and the interaction (chelation, adsorption) with gastric metals. In the present study, we tried to develop a rabbit model with low amounts of cationic metals in the stomach for preclinical oral bioavailability studies of chelating drugs. The elimination of gastric metals was achieved by preventing food intake and coprophagy and administering a low concentration of EDTA 2Na solution one day before experiments. Control rabbits were fasted but coprophagy was not prevented. The efficacy of rabbits treated with EDTA 2Na was evaluated by comparing the gastric contents, gastric metal contents and gastric pH between EDTA-treated and control rabbits. The treatment with more than 10 mL of 1 mg/mL EDTA 2Na solution decreased the amounts of gastric contents, cationic metals and gastric pH, without causing mucosal damage. The absolute oral bioavailabilities (mean values) of levofloxacin (LFX), ciprofloxacin (CFX) and tetracycline hydrochloride (TC), chelating antibiotics, were significantly higher in EDTA-treated rabbits than those in control rabbits as follows: 119.0 vs. 87.2%, 9.37 vs. 13.7%, and 4.90 vs. 2.59%, respectively. The oral bioavailabilities of these drugs were significantly decreased when Al(OH)₃ was administered concomitantly in both control and EDTA-treated rabbits. In contrast, the absolute oral bioavailabilities of ethoxycarbonyl 1-ethyl hemiacetal ester (EHE) prodrugs of LFX and CFX (LFX-EHE, CFX-EHE), which are non-chelating prodrugs at least in in vitro condition, were comparable between control and EDTA-treated rabbits irrespective of the presence of Al(OH)₃, although some variation was observed among rabbits. The oral bioavailabilities of LFX and CFX from their EHE prodrugs were comparable with LFX and CFX alone, respectively, even in the presence of Al(OH)₃. In conclusion, LFX, CFX and TC exhibited higher oral bioavailabilities in EDTA-treated rabbits than in control rabbits, indicating that the oral bioavailabilities of these chelating drugs are reduced in untreated rabbits. In conclusion, EDTA-treated rabbits were found to exhibit low gastric contents including metals and low gastric pH, without causing mucosal damage. Ester prodrug of CFX was effective in preventing chelate formation with Al(OH)₃ in vitro and in vivo, as well as in the case of ester prodrugs of LFX. EDTA-treated rabbits are expected to provide great advantages in preclinical oral bioavailability studies of various drugs and dosage formulations. However, a marked interspecies difference was still observed in the oral bioavailability of CFX and TC between EDTA-treated rabbits and humans, possibly due to the contribution of adsorptive interaction in rabbits. Further study is necessary to seek out the usefulness of the EDTA-treated rabbit with less gastric contents and metals as an experimental animal.

Advances in TEER measurements of biological barriers in microphysiological systems

Biological barriers are multicellular structures that precisely regulate the transport of ions, biomolecules, drugs, cells, and other organisms. Transendothelial/epithelial electrical resistance (TEER) is a label-free method for predicting the properties of biological barriers. Understanding the mechanisms that control TEER significantly enhances our knowledge of the physiopathology of different diseases and aids in the development of new drugs. Measuring TEER values within microphysiological systems called organ-on-a-chip devices that simulate the microenvironment, architecture, and physiology of biological barriers in the body provides valuable insight into the behavior of barriers in response to different drugs and pathogens. These integrated systems should increase the accuracy, reproducibility, sensitivity, resolution, high throughput, speed, cost-effectiveness, and reliable predictability of TEER measurements. Implementing advanced micro and nanoscale manufacturing techniques, surface modification methods, biomaterials, biosensors, electronics, and stem cell biology is necessary for integrating TEER measuring systems with organ-on-chip technology. This review focuses on the applications, advantages, and future perspectives of integrating organ-on-a-chip technology with TEER measurement methods for studying biological barriers. After briefly reviewing the role of TEER in the physiology and pathology of barriers, standard techniques for measuring TEER, including Ohm's law and impedance spectroscopy, and commercially available devices are described. Furthermore, advances in TEER measurement are discussed in multiple barrier-on-a-chip system models representing different organs. Finally, we outline future trends in implementing advanced technologies to design and fabricate nanostructured electrodes, complicated microfluidic chips, and membranes for more advanced and accurate TEER measurements.

3D In Vitro Blood-Brain-Barrier Model for Investigating Barrier Insults

Blood-brain-barrier (BBB) disruption has been associated with a variety of central-nervous-system diseases. In vitro BBB models enable to investigate how the barrier reacts to external injury events, commonly referred to as insults. Here, a human-cell-based BBB platform with integrated, transparent electrodes to monitor barrier tightness in real time at high resolution is presented. The BBB model includes human cerebral endothelial cells and primary pericytes and astrocytes in a 3D arrangement within a pump-free, open-microfluidic platform. With this platform, this study demonstrates that oxygen-glucose deprivation (OGD), which mimics the characteristics of an ischemic insult, induces a rapid remodeling of the cellular actin structures and subsequent morphological changes in the endothelial cells. High-resolution live imaging shows the formation of large actin stress-fiber bundles in the endothelial layer during OGD application, which ultimately leads to cell shrinkage and barrier breakage. Simultaneous electrical measurements evidence a rapid decrease of the barrier electrical resistance before the appearance of stress fibers, which indicates that the barrier function is compromised already before the appearance of drastic morphological changes. The results demonstrate that the BBB platform recapitulates the main barrier functions in vitro and can be used to investigate rapid reorganization of the BBB upon application of external stimuli.

Protein Substrate Alters Cell Physiology in Primary Culture of Vocal Fold Epithelial Cells

The basement membrane interacts directly with the vocal fold epithelium. Signaling between the basement membrane and the epithelium modulates gene regulation, differentiation, and proliferation. The purpose of this study was to identify an appropriate simple single-protein substrate for growth of rabbit vocal fold epithelial cells. Vocal folds from 3 New Zealand white rabbits (Oryctolagus cuniculus) were treated to isolate epithelial cells, and cells were seeded onto cell culture inserts coated with collagen I, collagen IV, laminin, or fibronectin. Transepithelial electrical resistance (TEER) was measured, and phase contrast microscopy, PanCK, CK14, and E-cadherin immunofluorescence were utilized to assess for epithelial cell-type characteristics. Further investigation via immunofluorescence labeling was conducted to assess proliferation (Ki67) and differentiation (Vimentin). There was a significant main effect of substrate on TEER, with collagen IV eliciting the highest, and laminin the lowest resistance. Assessment of relative TEER across cell lines identified a larger range of TEER in collagen I and laminin. Phase contrast imaging identified altered morphology in the laminin condition, but cell layer depth did not appear to be related to TEER, differentiation, or morphology. Ki67 staining additionally showed no significant difference in proliferation. All conditions had confluent epithelial cells and dispersed mesenchymal cells, with increased mesenchymal cell numbers over time; however, a higher proportion of mesenchymal cells was observed in the laminin condition. The results suggest collagen IV is a preferable basement membrane substrate for in vitro vocal fold epithelial primary cell culture, providing consistent TEER and characteristic cell morphology, and that laminin is an unsuitable substrate for vocal fold epithelial cells and may promote mesenchymal cell proliferation.

Impaired gastric mucosal integrity identified by confocal endomicroscopy in Helicobacter pylori-negative functional dyspepsia

BACKGROUND

Low-grade inflammation may be involved in the pathogenesis of functional dyspepsia (FD). We hypothesis that altered gastric permeability is involved in the onset and persistence of this disorder. Therefore, our aim was to evaluate gastric mucosal integrity and mast cell numbers in patients with FD.

METHODS

We enrolled 58 patients with FD fulfilling the Rome III criteria (H Pylori negative), 20 inflammatory control subjects (H Pylori positive), and 20 healthy controls (H Pylori negative). Probe-based confocal endomicroscopy was performed using intravenous fluorescein to assess the paracellular fluorescein leakage and cell shedding. Mast cells were identified with quantitative immunohistochemistry on mucosal biopsies.

KEY RESULTS

Endomicroscopic score of paracellular permeability was significantly higher in H pylori-negative FD patients compared with healthy controls (1.45 ± 1.27 vs 3.69 ± 3.18, P = .006). However, FD patients and healthy controls did not show differences in cell shedding score (0.75 ± 0.79 vs 1.29 ± 1.14, P = .069). Mast cell numbers were significantly increased compared with healthy control samples (18.91 ± 5.47 vs 14.1 ± 3.88, P < .001). The magnitude of increase in permeability was positively correlated with mast cell numbers of FD patients (rs = .6588, P < .0001), but not dyspepsia symptom scores.

CONCLUSION AND INFERENCES

Impaired gastric barrier function is present in FD patients. This might provide a new pathophysiological mechanism and therapeutical target in FD.

Replacing the Draize eye test: Impedance spectroscopy as a 3R method to discriminate between all GHS categories for eye irritation

Highly invasive animal based test procedures for risk assessment such as the Draize eye test are under increasing criticism due to poor transferability for the human organism and animal-welfare concerns. However, besides all efforts, the Draize eye test is still not completely replaced by alternative animal-free methods. To develop an in vitro test to identify all categories of eye irritation, we combined organotypic cornea models based on primary human cells with an electrical readout system that measures the impedance of the test models. First, we showed that employing a primary human cornea epithelial cell based model is advantageous in native marker expression to the primary human epidermal keratinocytes derived models. Secondly, by employing a non-destructive measuring system based on impedance spectroscopy, we could increase the sensitivity of the test system. Thereby, all globally harmonized systems categories of eye irritation could be identified by repeated measurements over a period of 7 days. Based on a novel prediction model we achieved an accuracy of 78% with a reproducibility of 88.9% to determine all three categories of eye irritation in one single test. This could pave the way according to the 3R principle to replace the Draize eye test.

A lower dose of fluorescein sodium is more suitable for confocal laser endomicroscopy: a feasibility study

BACKGROUND AND AIMS

Image quality can be guaranteed with the conventional dosage of fluorescein sodium in probe-based confocal laser endomicroscopy (pCLE). However, yellow discoloration of the skin seriously affects daily life and simultaneously increases the risk of adverse events such as allergic reactions. The aim of this study was to test whether a lower dosage of fluorescein sodium can provide satisfactory image quality and to compare the diagnostic accuracy of gastric intestinal metaplasia (GIM) through a randomized blind controlled trial.

METHODS

Consecutive patients were randomly assigned to different doses of fluorescein sodium. Image quality was determined by the endoscopists' subjective assessments and signal-to-noise ratio (SNR) assessment systems. Skin discoloration was tested using a neonatal transcutaneous jaundice detector. In addition, consecutive patients with a known or suspected diagnosis of GIM were examined by pCLE with the lower dose and the traditional dose.

RESULTS

Only 0.01 mL/kg dose of 10% fluorescein sodium led to a significant decrease in image quality (P < .05), and a dose of 0.02 mL/kg had the highest SNR value (P < .05). There were no significant differences in skin discoloration between the 0.01 mL/kg and 0.02 mL/kg doses (P = .148) and no statistical difference in the diagnostic accuracy of pCLE for GIM between the 0.02 mL/kg and 0.10 mL/kg doses (P > .05). The kappa values for the correlation between pCLE and histopathology were 0.867 (95% confidence interval, 0.782-0.952) and 0.891 (95% confidence interval, 0.811-0.971).

CONCLUSIONS

The 0.02 mL/kg dose of 10% fluorescein sodium seems to be the best dose for pCLE in the upper GI tract, with comparable image quality with the conventional dose and insignificant skin discoloration. This dose is also very efficient for the diagnosis of GIM.

Development of an Advanced Primary Human In Vitro Model of the Small Intestine

Intestinal in vitro models are valuable tools in drug discovery and infection research. Despite several advantages, the standard cell line-based Transwell(®) models based for example on colonic epithelial Caco-2 cells, lack the cellular complexity and transport activity associated with native small intestinal tissue. An additional experimental set-back arises from the most commonly used synthetic membranes, on which the cells are routinely cultured. These can lead to an additional barrier activity during in vitro testing. To overcome these limitations, we developed an alternative primary human small intestinal tissue model. This novel approach combines previously established gut organoid technology with a natural extracellular matrix (ECM) based on porcine small intestinal scaffold (SIS). Intestinal crypts from healthy human small intestine were expanded as gut organoids and seeded as single cells on SIS in a standardized Transwell-like setting. After only 7 days on the ECM scaffold, the primary cells formed an epithelial barrier while a subpopulation differentiated into intestinal specific cell types such as mucus-producing goblet cells or hormone-secreting enteroendocrine cells. Furthermore, we tested the influence of subepithelial fibroblasts and dynamic culture conditions on epithelial barrier function. The barrier integrity was stabilized by coculture in the presence of gut-derived fibroblasts. Compared to static or dynamic culture on an orbital shaker, dynamic culture in a defined perfusion bioreactor had an additional significant impact on epithelial cell differentiation, indicated by high prismatic cell morphology and upregulation of CYP3A4 enzyme and Mdr1 transporter activity. In summary, more physiological tissue models as presented in our study might be useful tools in preclinical research and development.

Single-Pass Intestinal Perfusion (SPIP) and prediction of fraction absorbed and permeability in humans: A study with antiretroviral drugs

In recent years, the prediction of oral drug absorption in humans has been a challenge for researchers and many techniques for permeability studies have been developed for several purposes, including biowaiver processes. The Single-Pass Intestinal Perfusion (SPIP) method performed in rats can provide permeability results closest to in vivo condition. The purpose of the present study was to evaluate the intestinal permeability of the antiretroviral drugs lamivudine, stavudine and zidovudine using the SPIP method in rats and to predict their permeability (Peff,humans) and fraction absorbed (Fa) in humans. Metoprolol and fluorescein were used as marker compounds of high and low permeability, respectively. The effective permeability (Peff) results showed that stavudine and zidovudine have high permeability characteristics while lamivudine presented the lowest result. From Peff values obtained in rats, the Peff,humans and Fa were calculated. The use of SPIP in rats and calculations for absorption prediction in humans may indicate the transport mechanisms and/or pre-systemic metabolism involved on permeation processes of drugs, since this model is the closest to in vivo conditions.

Herb-partitioned moxibustion upregulated the expression of colonic epithelial tight junction-related proteins in Crohn's disease model rats

BACKGROUND

Herb-partitioned moxibustion (HPM) at Tianshu (ST25) and Qihai (RN6) has been used to treat Crohn's disease (CD). Injury to intestinal epithelial tight junctions (TJs) is the leading cause of CD onset with under expression of TJ-related proteins such as occludin, claudin-1, and zonula occludens protein-1 (ZO-1). This study aimed to investigate whether HPM can change the permeability of the intestinal epithelial barrier by affecting the expression of colonic epithelial TJ-related proteins in vitro.

METHODS

Forty-eight male Sprague-Dawley rats were randomly divided into four groups of twelve rats: normal control (NC) group; model control (MC) group; herb-partitioned moxibustion (HPM) group; and mesalazine control (MESA) group. The rats in the latter three groups were given trinitrobenzene sulfonic acid (TNBS) enemas to establish CD models. The HPM group was treated with HPM at Tianshu (ST25) and Qihai (RN6) once daily for 14 consecutive days, while the MESA group was given mesalazine solution (at the proportion of 0.018:1) by lavage twice daily for the same period. After the treatment period, the colon tissues from all groups were partly processed for macroscopic damage assessment and histological observation, and partly purified and cultured in vitro to examine the permeability of the intestinal epithelial cell barrier by trans-epithelial electrical resistance (TEER). Western blot and fluorescence quantitative polymerase chain reaction (FQ-PCR) analyses were performed to observe the expression of occludin, claudin-1, and ZO-1 proteins and mRNAs, respectively.

RESULTS

In the HPM and MESA groups, the typical CD macroscopic damage, i.e., inflammatory cell infiltration in colonic mucosa and submucosa, submucosal lymphoid follicular hyperplasia, hyperemia and edema, and morphological changes were improved to different degrees in the colonic tissues (HPM, MESA vs. MC for macroscopic score of colonic damage: all P < 0.001). The decreasing tendencies were minor for colonic TEER values (HPM, MESA vs. MC: all P < 0.001), and expression of intestinal epithelial TJ-related proteins (HPM, MESA vs. MC: all P < 0.05) and mRNAs (HPM, MESA vs. MC: all P < 0.05), especially in the HPM group (HPM vs. MESA for TEER values: P < 0.001).

CONCLUSIONS

HPM at Tianshu (ST25) and Qihai (RN6) upregulated the expression of occludin, claudin-1, and ZO-1 in TNBS-induced CD model rats.

Characterization of animal models for primary sclerosing cholangitis (PSC)

Primary sclerosing cholangitis (PSC) is a chronic cholangiopathy characterized by biliary fibrosis, development of cholestasis and end stage liver disease, high risk of malignancy, and frequent need for liver transplantation. The poor understanding of its pathogenesis is also reflected in the lack of effective medical treatment. Well-characterized animal models are utterly needed to develop novel pathogenetic concepts and study new treatment strategies. Currently there is no consensus on how to evaluate and characterize potential PSC models, which makes direct comparison of experimental results and effective exchange of study material between research groups difficult. The International Primary Sclerosing Cholangitis Study Group (IPSCSG) has therefore summarized these key issues in a position paper proposing standard requirements for the study of animal models of PSC.

Retinoic acid and hydrocortisone strengthen the barrier function of human RPMI 2650 cells, a model for nasal epithelial permeability

The nasal pathway represents an alternative route for non-invasive systemic administration of drugs. The main advantages of nasal drug delivery are the rapid onset of action, the avoidance of the first-pass metabolism in the liver and the easy applicability. In vitro cell culture systems offer an opportunity to model biological barriers. Our aim was to develop and characterize an in vitro model based on confluent layers of the human RPMI 2650 cell line. Retinoic acid, hydrocortisone and cyclic adenosine monophosphate, which influence cell attachment, growth and differentiation have been investigated on the barrier formation and function of the nasal epithelial cell layers. Real-time cell microelectronic sensing, a novel label-free technique was used for dynamic monitoring of cell growth and barrier properties of RPMI 2650 cells. Treatments enhanced the formation of adherens and tight intercellular junctions visualized by electron microscopy, the presence and localization of junctional proteins ZO-1 and β-catenin demonstrated by fluorescent immunohistochemistry, and the barrier function of nasal epithelial cell layers. The transepithelial resistance of the RPMI 2650 cell model reached 50 to 200 Ω × cm(2), the permeability coefficient for 4.4 kDa FITC-dextran was 9.3 to 17 × 10(-6) cm/s, in agreement with values measured on nasal mucosa from in vivo and ex vivo experiments. Based on these results human RPMI 2650 cells seem to be a suitable nasal epithelial model to test different pharmaceutical excipients and various novel formulations, such as nanoparticles for toxicity and permeability.

In vitro assessment of epithelial electrical resistance in human esophageal and jejunal mucosae and in Caco-2 cell layers

OBJECTIVE

There is a need for a technique allowing studies of human mucosal specimens collected during different clinical conditions. This study elucidates if square wave pulse analysis discriminates between epithelial and transmural electrical resistance and if there is an association with transepithelial permeability of molecular probes.

METHODS

Mucosae from esophagus (surgical resections: n = 14; endoscopic biopsies: n = 15) and jejunum (n = 12) and Caco-2 cell monolayers were investigated in Ussing chambers. Transmural and epithelial electrical resistance were recorded by the use of standardized current pulses. Permeability was assessed using two fluorescein-labeled probes (weight 376 and 4000 Da).

RESULTS

Baseline epithelial electrical resistance was higher in esophageal mucosa (~280 Ω*cm(2)), than in jejunal (~10 Ω*cm(2)) and Caco-2 cells (~140 Ω*cm(2)). The subepithelial contribution to the transmural resistance was higher in jejunal preparations (+88%) and Caco-2 cells (+75%), than in esophageal (+30%). During hypoxia the subepithelial resistance was unchanged, whereas the epithelial resistance decreased significantly in jejunal mucosa and Caco-2 cells. These findings coincided with increased transepithelial probe permeability and signs of disturbed morphology. Esophageal epithelia were resistant to hypoxia. However, exposure to deoxycholic acid and trypsin abolished the esophageal epithelial resistance and increased probe permeability. Endoscopic esophageal biopsies from patients with erosive reflux disease exhibited significantly lower epithelial resistance and higher current than healthy subjects.

CONCLUSION

Square wave pulse analysis in Ussing chambers is suitable for assessment of epithelial electrical resistance that can reflect transepithelial permeability of molecular probes with known size. Moreover, the technique discriminated between healthy and reflux-diseased esophageal mucosal biopsies.

Mucosal barrier defects in gastric intestinal metaplasia: in vivo evaluation by confocal endomicroscopy

BACKGROUND

Helicobacter pylori infection and intestinal metaplasia (IM) are associated with gastric cancer. An impaired gastric mucosal barrier could be involved in this carcinogenesis.

OBJECTIVE

To evaluate laser confocal laser endomicroscopy (CLE) for in vivo functional imaging of mucosal barrier defects in patients with IM.

DESIGN

Prospective, controlled study.

SETTING

A tertiary-care academic center.

PATIENTS

This study involved patients with IM of the gastric mucosa who underwent CLE for surveillance.

INTERVENTIONS

Specific IM mucosa and non-IM mucosa in patients were identified by CLE, and targeted biopsy samples were taken for histopathology and electron microscopy.

MAIN OUTCOME MEASUREMENTS

Post-CLE assessment of paracellular fluorescein leakage was devised and validated by electron microscopy. We also evaluated the effect of H pylori eradication on the mucosal barrier.

RESULTS

Forty-two patients were included. Of non-IM samples, the paracellular permeability was significantly increased in H pylori-positive samples compared with H pylori-negative controls (54 ± 31% vs 3 ± 6%, P < .05). Of IM samples, the permeability was significantly increased in both H pylori-negative and H pylori-positive samples (67 ± 34% and 72 ± 28% vs 3 ± 6%, both P < .05). The results of post-CLE assessment correlated well with the electron microscopy findings (R(2) 0.834, P < .0001). After the eradication of H pylori, the paracellular barrier dysfunction of non-IM mucosa was significantly improved as shown by electron microscopy and CLE (both P < .001). However, there was no significant change in IM mucosa.

LIMITATIONS

Single-center study.

CONCLUSIONS

CLE allows functional imaging of mucosal barrier defects. Gastric IM is associated with an impaired paracellular barrier irrespective of H pylori eradication.