Short term Caco-2/TC7 cell culture: comparison between conventional 21-d and a commercially available 3-d system

Short Caco-2 model for evaluation of drug permeability: A sodium valerate-assisted approach

The human colorectal adenocarcinoma cell line Caco-2, widely used for studying intestinal drug permeability, is typically grown on permeable filter supports and matures in 21 days with frequent media changes. The process is labor-intensive, prone to contamination, and has low throughput, contributing to the overall high utilization cost. Efforts to establish a low-cost, high-throughput, and short-duration model have encountered obstacles, such as weaker tight junctions causing monolayer leaks, incomplete differentiation resulting in low transporter expression, intricate and challenging protocols, and cytotoxicity, limiting the usability. Hence, this study aimed to develop a low-cost, efficient, and short-duration model by addressing the aforementioned concerns by customizing the media and finding a safe differentiation inducer. We generated a new rapid model using sodium valerate, which demonstrated sufficient transporter activity, improved monolayer integrity, and higher levels of differentiation markers than the 21-day model. Furthermore, this model exhibited consistent and reliable results when used to evaluate drug permeability over multiple days of repeated use. This study demonstrates the potential of a sodium valerate-assisted abbreviated model for drug permeability assessment with economic and practical advantages.

Does Bentonite Cause Cytotoxic and Whole-Transcriptomic Adverse Effects in Enterocytes When Used to Reduce Aflatoxin B1 Exposure?

Aflatoxin B1 (AFB1) is a major food safety concern, threatening the health of humans and animals. Bentonite (BEN) is an aluminosilicate clay used as a feed additive to reduce AFB1 presence in contaminated feedstuff. So far, few studies have characterized BEN toxicity and efficacy in vitro. In this study, cytotoxicity (WST-1 test), the effects on cell permeability (trans-epithelial electrical resistance and lucifer yellow dye incorporation), and transcriptional changes (RNA-seq) caused by BEN, AFB1 and their combination (AFB1 + BEN) were investigated in Caco-2 cells. Up to 0.1 mg/mL, BEN did not affect cell viability and permeability, but it reduced AFB1 cytotoxicity; however, at higher concentrations, BEN was cytotoxic. As to RNA-seq, 0.1 mg/mL BEN did not show effects on cell transcriptome, confirming that the interaction between BEN and AFB1 occurs in the medium. Data from AFB1 and AFB1 + BEN suggested AFB1 provoked most of the transcriptional changes, whereas BEN was preventive. The most interesting AFB1-targeted pathways for which BEN was effective were cell integrity, xenobiotic metabolism and transporters, basal metabolism, inflammation and immune response, p53 biological network, apoptosis and carcinogenesis. To our knowledge, this is the first study assessing the in vitro toxicity and whole-transcriptomic effects of BEN, alone or in the presence of AFB1.

A liposome-micelle-hybrid (LMH) oral delivery system for poorly water-soluble drugs: Enhancing solubilisation and intestinal transport

A novel liposome-micelle-hybrid (LMH) carrier system was developed as a superior oral drug delivery platform compared to conventional liposome or micelle formulations. The optimal LMH system was engineered by encapsulating TPGS micelles in the aqueous core of liposomes and its efficacy for oral delivery was demonstrated using lovastatin (LOV) as a model poorly soluble drug with P-gp (permeability glycoprotein) limited intestinal absorption. LOV-LMH was characterised as unilamellar, spherical vesicles encapsulating micellar structures within the interior aqueous core and showing an average diameter below 200 nm. LMH demonstrated enhanced drug loading, water apparent solubility and extended/controlled release of LOV compared to conventional liposomes and micelles. LMH exhibited enhanced LOV absorption and transportation in a Caco-2 cell monolayer model of the intestine by inhibiting the P-gp transporter system compared to free LOV. The LMH system is a promising novel oral delivery approach for enhancing bioavailability of poorly water-soluble drugs, especially those presenting P-gp effluxes limited absorption.

Insights into amebiasis using a human 3D-intestinal model

Entamoeba histolytica is the causative agent of amebiasis, an infectious disease targeting the intestine and the liver in humans. Two types of intestinal infection are caused by this parasite: silent infection, which occurs in the majority of cases, and invasive disease, which affects 10% of infected persons. To understand the intestinal pathogenic process, several in vitro models, such as cell cultures, human tissue explants or human intestine xenografts in mice, have been employed. Nevertheless, our knowledge on the early steps of amebic intestinal infection and the molecules involved during human-parasite interaction is scarce, in part due to limitations in the experimental settings. In the present work, we took advantage of tissue engineering approaches to build a three-dimensional (3D)-intestinal model that is able to replicate the general characteristics of the human colon. This system consists of an epithelial layer that develops tight and adherens junctions, a mucus layer and a lamina propria-like compartment made up of collagen containing macrophages and fibroblast. By means of microscopy imaging, omics assays and the evaluation of immune responses, we show a very dynamic interaction between E. histolytica and the 3D-intestinal model. Our data highlight the importance of several virulence markers occurring in patients or in experimental models, but they also demonstrate the involvement of under described molecules and regulatory factors in the amoebic invasive process.

Multiparametric temporal analysis of the Caco-2/TC7 demonstrated functional and differentiated monolayers as early as 14 days of culture

Reducing the differentiation period for obtaining an in vitro intestinal barrier model is required to reduce the duration and cost for drug screening assays. In this frame, the Caco-2/TC7 subclone differentiation state was investigated from day 0 (D0) to day 32 (D32). As such, the expression of 45 genes (including cell junction, cell polarization, cell functionality, drug transport and metabolism genes) was followed throughout the 32 days. In parallel, the monolayer polarization and the formation of the cellular junctions were characterized by the immuno-staining of occludin, claudin-1 and actin proteins. The cell monolayer permeability was analyzed via transepithelial electric resistance measurements and paracellular transport of Lucifer Yellow. The P-gp efflux efficiency was assessed by rhodamine 123 transport. Alkaline phosphate activity was quantified to assess the cell differentiation. Three stages of differentiation were observed using the clustering of principal component analysis of the RTqPCR data and the overall assays. From D0 to D10, cells were in a proliferation stage and under-differentiated; from D14 to D21 a stable differentiation stage was reached; from D25 to D32 the epithelium seemed to enter into a post-differentiated stage. This study demonstrates that Caco-2/TC7 cells are functional and ready for use in drug screening permeability assays from 14 days in culture when compared with conventional 21 days for Caco-2 cells. In addition, this study provides a refined set of data allowing temporal and multi scale investigations, due to the intracellular kinetics and mRNA levels that can be correlated with membrane protein kinetics and functional extracellular activities. Therefore, shorter time in culture combined with a better knowledge of the cells during the time in culture will in turn help to improve the quality and cost of Caco-2/TC7 assays for drug development.

TEER measurement techniques for in vitro barrier model systems

Transepithelial/transendothelial electrical resistance (TEER) is a widely accepted quantitative technique to measure the integrity of tight junction dynamics in cell culture models of endothelial and epithelial monolayers. TEER values are strong indicators of the integrity of the cellular barriers before they are evaluated for transport of drugs or chemicals. TEER measurements can be performed in real time without cell damage and generally are based on measuring ohmic resistance or measuring impedance across a wide spectrum of frequencies. The measurements for various cell types have been reported with commercially available measurement systems and also with custom-built microfluidic implementations. Some of the barrier models that have been widely characterized using TEER include the blood-brain barrier (BBB), gastrointestinal (GI) tract, and pulmonary models. Variations in these values can arise due to factors such as temperature, medium formulation, and passage number of cells. The aim of this article is to review the different TEER measurement techniques and analyze their strengths and weaknesses, determine the significance of TEER in drug toxicity studies, examine the various in vitro models and microfluidic organs-on-chips implementations using TEER measurements in some widely studied barrier models (BBB, GI tract, and pulmonary), and discuss the various factors that can affect TEER measurements.

Watermelon juice: potential functional drink for sore muscle relief in athletes

l-Citrulline is an excellent candidate to reduce muscle soreness, and watermelon is a fruit rich in this amino acid. This study investigated the potential of watermelon juice as a functional drink for athletes. An in vitro study of intestinal absorption of l-citrulline in Caco-2 cells was performed using unpasteurized (NW), pasteurized (80 °C for 40 s) watermelon juice (PW) and, as control, a standard of l-citrulline. l-citrulline bioavailability was greater when it was contained in a matrix of watermelon and when no heat treatment was applied. In the in vivo experiment (maximum effort test in a cycloergometer), seven athletes were supplied with 500 mL of natural watermelon juice (1.17 g of l-citrulline), enriched watermelon juice (4.83 g of l-citrulline plus 1.17 g from watermelon), and placebo. Both watermelon juices helped to reduce the recovery heart rate and muscle soreness after 24 h.

Inhibition of dipeptidyl peptidase activity by flavonol glycosides of guava (Psidium guajava L.): a key to the beneficial effects of guava in type II diabetes mellitus

Based on the traditional use in popular medicine, the effect of extracts from Psidium guajava L. leaves and of the main flavonol-glycoside components on dipeptidyl-peptidase IV (DP-IV), a key enzyme of blood glucose homoeostasis, has been investigated in-vitro. An ethanolic extract was prepared from dried, powdered leaves of guava and was found to contain seven main flavonol-glycosides, which were isolated by semipreparative HPLC and tested individually. The ethanolic guava leave extract was shown to exert a dose-dependent inhibition of DP-IV, with an IC50 of 380 μg/ml test assay solution. Also the individual flavonol-glycosides inhibited DP-IV dose-dependently, with variations of the effects by a factor of 10, and an overall effect accounting for 100% of that observed for the total guava extract. The recovery of individual flavonol-glycosides in CaCo-2 epithelial cells, a model of gastrointestinal tract absorption, amounted to 2.3-5.3% of the amount available for absorption over 60 min at 37°C.

Antihypertensive and Laxative Effects by Pharmacological Inhibition of Sodium-Proton-Exchanger Subtype 3–Mediated Sodium Absorption in the Gut

High intestinal sodium absorption is one mechanism of hypertension and constipation. The sodium-proton-exchanger subtype 3 (NHE3) is an important mediator of sodium absorption in the gut. SAR218034 (SAR) is an orally nonabsorbable specific NHE3 inhibitor. The effect of SAR (1 mg/kg per day in chow) on feces sodium excretion, systolic blood pressure via tail cuff, and gene expression of NHE3 in the gut were studied in senescent lean hypertensive rats (spontaneously hypertensive rats-lean, loaded with NaCl 0.7% in drinking water) and in hypertensive, obese, and hyperinsulinemic rats (spontaneously hypertensive rats-obese, not loaded with NaCl). In spontaneously hypertensive rats-lean, inhibition of intestinal NHE3 by SAR increased feces sodium excretion and reduced urinary sodium excretion, whereas absolute sodium balance and serum sodium concentration were not changed. This suggests reduced intestinal sodium absorption in SAR-treated animals and was associated with increased feces water content (58% versus 42% in placebo treated animals; P =0.0001) and reduction in systolic blood pressure from 222±7 to 198±2 mm Hg ( P =0.0001). Angiotensin-converting enzyme inhibition by ramipril plus NHE3 inhibition resulted in an additive blood pressure–lowering effect. In spontaneously hypertensive rats-obese, SAR lowered systolic blood pressure but did not modify serum insulin or cholesterol levels. Gene expression of NHE3 was upregulated in the ileum and colon but not in the jejunum of SAR-treated rats. Reduction of intestinal sodium absorption by selective NHE3 inhibition in the gut reduces high blood pressure and increases feces water excretion. Intestinal NHE3 blockade could be a new treatment strategy for elderly patients suffering from high blood pressure and constipation.

Cell-based in vitro models for predicting drug permeability

INTRODUCTION

In vitro cell models have been used to predict drug permeation in early stages of drug development, since they represent an easy and reproducible method, allowing the tracking of drug absorption rate and mechanism, with an advantageous cost-benefit ratio. Such cell-based models are mainly composed of immortalized cells with an intrinsic ability to grow in a monolayer when seeded in permeable supports, maintaining their physiologic characteristics regarding epithelium cell physiology and functionality.

AREAS COVERED

This review summarizes the most important intestinal, pulmonary, nasal, vaginal, rectal, ocular and skin cell-based in vitro models for predicting the permeability of drugs. Moreover, the similitude between in vitro cell models and in vivo conditions are discussed, providing evidence that each model may provisionally resemble different drug absorption route.

EXPERT OPINION

Despite the widespread use of in vitro cell models for drug permeability and absorption evaluation purposes, a detailed study on the properties of these models and their in vitro-in vivo correlation compared with human data are required to further use in order to consider a future drug discovery optimization and clinical development.

Novel and established intestinal cell line models - An indispensable tool in food science and nutrition

This review presents the applications of intestinal cell models of human and pig origin in food and nutritional sciences and highlights their potential as in vitro platforms for preclinical research. Intestinal cell models are used in studies of bioavailability, adsorption and transport in nutritional or toxicological settings, allergic effects of food components, as well as probiotics and/or host-pathogen gut interactions. In addition, this review discusses the advantages of using specialized and functional cell models over generic cancer-derived cell lines.

Optimizing culture conditions of a porcine epithelial cell line IPEC-J2 through a histological and physiological characterization

The high similarity between pigs and humans makes pigs a good gastrointestinal (GI) model for humans. Recently an epithelial cell line originating from the jejunum of pig (IPEC-J2) became available. Once validated, this model can be used to investigate the complex interactions occurring in the intestine. The advantages of using IPEC-J2 as in vitro model of the GI tract are the high resemblance between humans and pigs, and the ease of extrapolating in vitro to in vivo characteristics. In this study, the IPEC-J2 cells were functionally characterized by measuring the trans-epithelial electrical resistance (TEER), and by histological and ultrastructural studies. IPEC-J2 cells grown on six different permeable support systems, were investigated. The Transwell(®)-COL collagen-coated membrane (1.12 cm(2)) showed the best results concerning time efficiency and TEER values. The optimum seeding density of 12 × 10(5) cells/mL ensured that after 9 days of differentiation a confluent monolayer was formed. The decrease in TEER values after a maximum had been reached, coincided with the ultrastructural development of apical microvilli. We conclude that IPEC-J2 cells grown on collagen-coated membranes represent a valuable in vitro model system for the small intestinal epithelium which can be of great interest for intestinal research.

Kinetic modelling of passive transport and active efflux of a fluoroquinolone across Caco-2 cells using a compartmental approach in NONMEM

The purpose was to develop a general mathematical model for estimating passive permeability and efflux transport parameters from in vitro cell culture experiments. The procedure is applicable for linear and non-linear transport of drug with time, <10 or >10% of drug transport, negligible or relevant back flow, and would allow the adequate correction in the case of relevant mass balance problems. A compartmental kinetic approach was used and the transport barriers were described quantitatively in terms of apical and basolateral clearances. The method can be applied when sink conditions are not achieved and it allows the evaluation of the location of the transporter and its binding site. In this work it was possible to demonstrate, from a functional point of view, the higher efflux capacity of the TC7 clone and to identify the apical membrane as the main resistance for the xenobiotic transport. This methodology can be extremely useful as a complementary tool for molecular biology approaches in order to establish meaningful hypotheses about transport mechanisms.

The Caco-2 cell monolayer: usefulness and limitations

BACKGROUND

The Caco-2 monolayer has been used extensively for the high-throughput screening of drug permeability and identification of substrates, inhibitors, and inducers of intestinal transporters, especially P-glycoprotein (P-gp). Traditionally, the Caco-2 monolayer is viewed as a single barrier rather than a polarized cell monolayer consisting of metabolic enzymes that are sandwiched between two membrane barriers with distinctly different transporters.

OBJECTIVE

This review addressed the usefulness and limitations of the Caco-2 cell monolayer in drug discovery and mechanistic studies.

METHODS

This mini-review covered applications of the Caco-2 monolayer, clarified misconceptions, and critically addressed issues on data interpretation.

CONCLUSION

The catenary model extends the usefulness of Caco-2 monolayer and provides proper mechanistic insight and data interpretation.

Sublingual Delivery of Insulin: Effects of Enhancers on the Mucosal Lipid Fluidity and Protein Conformation, Transport, and in Vivo Hypoglycemic Activity

The purposes of this study were to evaluate effects of enhancers for sublingual delivering insulin on the mucosal lipid fluidity and protein conformation, transport, and in vivo hypoglycemic activity in normal rats. The effects on sublingual mucosa, and aggregation states of insulin were estimated using fluorescence polarization, and circular dichroism method, respectively. The human immortalized oral epithelial cell monolayer was used for evaluating transport of insulin. Hydroxylpropyl-beta-cyclodextrin (HP-beta-CD), chitosan, polyethylene-polypropylene glycol, polyoxyethylene lauryl ether, polysorbate 80, egg lecithin, or oleic acid, was used as a penetration enhancer, respectively. The fluidity of sublingual mucosal lipid was markedly reduced by these enhancers excluding polysorbate 80, and the secondary structure of the mucosal proteins was also influenced by these enhancers. The hexamers of insulin were dissociated to monomers only by chitosan, polyoxyethylene lauryl ether, and egg lecithin. Nonetheless, plasma glucose levels in normal rats were significantly lowered after sublingual administration of insulin with an enhancer compared with those without an enhancer at the same time-point. The enhancing effects may be due to one or multiple factors: increasing the mucosal lipid fluidity, directly loosing the tight junction of epithelia, and dissociating the hexamers of insulin to monomers. Among these, the opened tight junction may correlate most with the enhancing effect in the mucosal permeability. Because the aggregates of insulin exist, the dissociation of the aggregates by an enhancer would benefit the permeability.

"If we can just 'stall' new unfriendly legislations, the scoreboard is already in our favour": transnational tobacco companies and ingredients disclosure in Thailand

OBJECTIVES

To review the strategies employed by overseas cigarette manufacturers operating in Thailand to obstruct the passage and subsequent enforcement of national public health legislation, specifically the ingredients disclosure provision of the 1992 Tobacco Products Control Act.

METHODS

Analysis of previously confidential tobacco industry documents relevant to non-compliance with the ingredients disclosure legislation.

RESULTS

Requirement for disclosure of ingredients contained in cigarettes contained in the Tobacco Products Control Act was identified by transnational tobacco companies (TTCs) not only as a significant threat to their operations in Thailand, but as a dangerous global precedent. Industry documents reveal a determined campaign to block, stall, or amend the proposed regulation during the legislative process. Industry representatives petitioned the Ministry of Health to revise the requirement from by brand disclosure to a more palatable by company submission. Strategies were adapted in the wake of the passage of the Act. Most significantly, the industry in concert with embassies in Bangkok threatened the Thai government with appeals to international trade bodies on the grounds of violation of international agreements. Industry documents also reveal that as submission of ingredient lists appeared unavoidable, leading companies operating in Thailand endeavoured to confound the disclosure requirement by disguising ingredients and reformulating brand recipes.

CONCLUSIONS

The evidence presented highlights the importance of ingredients regulation and demonstrates how health policy can be transformed during its implementation. A greater understanding of trade agreements emerges as a priority for global tobacco control.