Development, validation, and application of a novel 7-day Caco-2 cell culture system

Rebamipide nanocrystal with improved physicomechanical properties and its assessment through bio-mimicking 3D intestinal permeability model

This study investigated the formulation and characterization of rebamipide nanocrystals (REB-NCs) to enhance the solubility and permeability of rebamipide, an anti-ulcer medication known for its low aqueous solubility and permeability, classified as BCS class IV. Employing high-pressure homogenization and wet milling techniques, we successfully achieved nanonization of rebamipide, resulting in stable nanosuspensions that were subsequently freeze-dried to produce REB-NCs with an average particle size of 223 nm. Comprehensive characterization techniques, including Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), and differential scanning calorimetry (DSC) confirmed the crystalline nature of the nanocrystals and their compatibility with the selected excipients. The saturation solubility study revealed a remarkable three-fold enhancement in PBS pH 7.4 compared to rebamipide API, indicating the effectiveness of the nanocrystal formulation in improving drug solubility. Furthermore, 3D in-vitro permeability assessments conducted on Caco-2 cell monolayers demonstrated an noticeable increase in the permeability of REB-NCs relative to the pure active pharmaceutical ingredient (API), highlighting the promise of this formulation to enhance drug absorption. The dissolution profile of the nanocrystal tablets exhibited immediate release characteristics, significantly outperforming conventional formulations in terms of the dissolution rate. This research underscores the potential of nanomilling as a scalable, environment-friendly, and less toxic approach to significantly enhance the bioavailability of rebamipide. By addressing the challenges associated with the solubility and permeability of poorly water-soluble drugs, our outcome offers insightful information into developing efficient nanomedicine strategies for enhancing therapeutic outcomes.

Bioengineering Human Upper Respiratory Mucosa: A Systematic Review of the State of the Art of Cell Culture Techniques

BACKGROUND

The upper respiratory mucosa plays a crucial role in both the physical integrity and immunological function of the respiratory tract. However, in certain situations such as infections, trauma, or surgery, it might sustain damage. Tissue engineering, a field of regenerative medicine, has found applications in various medical fields including but not limited to plastic surgery, ophthalmology, and urology. However, its application to the respiratory system remains somewhat difficult due to the complex morphology and histology of the upper respiratory tract. To date, a culture protocol for producing a handleable, well-differentiated nasal mucosa has yet to be developed. The objective of this review is to describe the current state of research pertaining to cell culture techniques used for producing autologous healthy human upper respiratory cells and mucosal tissues, as well as describe its clinical applications.

METHODS

A search of the relevant literature was carried out with no time restriction across Embase, Cochrane, PubMed, and Medline Ovid databases. Keywords related to "respiratory mucosa" and "culture techniques of the human airway" were the focus of the search strategy for this review. The risk of bias in retained studies was assessed using the Joanna Briggs Institute's (JBI) critical appraisal tools for qualitative research. A narrative synthesis of our results was then conducted.

RESULTS

A total of 33 studies were included in this review, and thirteen of these focused solely on developing a cell culture protocol without further use. The rest of the studies used their own developed protocol for various applications such as cystic fibrosis, pharmacological, and viral research. One study was able to develop a promising model for nasal mucosa that could be employed as a replacement in nasotracheal reconstructive surgery.

CONCLUSIONS

This systematic review extensively explored the current state of research regarding cell culture techniques for producing tissue-engineered nasal mucosa. Bioengineering the nasal mucosa holds great potential for clinical use. However, further research on mechanical properties is essential, as the comparison of engineered tissues is currently focused on morphology rather than comprehensive mechanical assessments.

Novel In Vitro Models for Cell Differentiation and Drug Transport Studies of the Human Intestine

The most common in vitro model for absorption, distribution, metabolism, and excretion (ADME) purposes is currently the Caco-2 cell line. However, clear differences in gene and protein expression towards the small intestine and an, at best, fair prediction accuracy of intestinal drug absorption restrict the usefulness of a model for intestinal epithelial cells. To overcome these limitations, we evaluated a panel of low-passaged patient-derived colorectal cancer cell lines of the HROC collection concerning similarities to small intestinal epithelial cells and their potential to predict intestinal drug absorption. After initial screening of a larger panel, ten cell lines with confluent outgrowth and long-lasting barrier-forming potential were further characterized in close detail. Tight junctional complexes and microvilli structures were detected in all lines, anda higher degree of differentiation was observed in 5/10 cell lines. All lines expressed multiple transporter molecules, with the expression levels in three lines being close to those of small intestinal epithelial cells. Compared with the Caco-2 model, three HROC lines demonstrated both higher similarity to jejunal epithelial tissue cells and higher regulatory potential of relevant drug transporters. In summary, these lines would be better-suited human small intestinal epithelium models for basic and translational research, especially for ADME studies.

Challenges and Opportunities in the Oral Delivery of Recombinant Biologics

Recombinant biological molecules are at the cutting-edge of biomedical research thanks to the significant progress made in biotechnology and a better understanding of subcellular processes implicated in several diseases. Given their ability to induce a potent response, these molecules are becoming the drugs of choice for multiple pathologies. However, unlike conventional drugs which are mostly ingested, the majority of biologics are currently administered parenterally. Therefore, to improve their limited bioavailability when delivered orally, the scientific community has devoted tremendous efforts to develop accurate cell- and tissue-based models that allow for the determination of their capacity to cross the intestinal mucosa. Furthermore, several promising approaches have been imagined to enhance the intestinal permeability and stability of recombinant biological molecules. This review summarizes the main physiological barriers to the oral delivery of biologics. Several preclinical in vitro and ex vivo models currently used to assess permeability are also presented. Finally, the multiple strategies explored to address the challenges of administering biotherapeutics orally are described.

Heterogenous morphogenesis of Caco-2 cells reveals that flow induces three-dimensional growth and maturation at high initial seeding cell densities

Here, we introduce a customized hanging insert fitting a six-well plate to culture Caco-2 cells on hydrogel membranes under flow conditions. The cells are cultured in the apical channel-like chamber, which provides about 1.3 dyn/cm² shear, while the basolateral chamber is mixed when the device is rocked. The device was tested by investigating the functional impact of the initial seeding density in combination with flow applied at confluency. The low seeding density cultures grew in two dimensional (2D) irrespective of the flow. Flow and higher seeding density resulted in a mixture of three dimensional (3D) structures and 2D layers. Static culture and high cell seeding density resulted in 2D layers. The flow increased the height and ZO-1 expression of cells in 2D layers, which correlated with an improved barrier function. Cultures with 3D structures had higher ZO-1 expression than 2D cultures, but this did not correlate with an increased barrier function. 2D monolayers in static and dynamic cultures had similar morphology and heterogeneity in the expression of Mucin-2 and Villin, while the 3D structures had generally higher expression of these markers. The result shows that the cell density and flow determine 3D growth and that the highest barrier function was obtained with low-density cultures and flow.

The Caco-2 Model: Modifications and enhancements to improve efficiency and predictive performance

The Caco-2 cell model has been widely used to assess the permeability of drug candidates. It has provided a high throughput in vitro platform, functionally resembling the enterocytes. Since the oral route is the most preferred for drug administration, the Caco-2 cell model acts as a very important tool to elucidate the oral "druggability" of a molecule by providing a fairly reliable estimate of its permeability through the intestinal membrane. Despite its shortcomings (the lack of a mucus layer, long cultivation period, inter-lab variability, and differences in expression of enzymes, transporters, and tight junction complexes) it remains heavily used due to its reliability, predictive performance, and wide acceptance. Various modifications have been made: co-culturing with other intestinal cells, applying biosimilar mucus, reducing culturing time, combining Caco-2 monolayer with the dissolution apparatus, enhancing protein expression, and redesigning the sampling apparatus. These modifications are intended to overcome some of the shortcomings of the Caco-2 model in order to make its use easier, quicker, economical, and more representative of the intestine. The aim of this review is to discuss such modifications to enhance this model's utility, predictive performance, and reproducibility.

Application of Fucoidan in Caco-2 Model Establishment

The Caco-2 model is a common cell model for material intestinal absorption in vitro, which usually takes 21 days to establish. Although some studies have shown that adding puromycin (PM) can shorten the model establishment period to 7 days, this still requires a long modeling time. Therefore, exploring a shorter modeling method can reduce the experimental costs and promote the development and application of the model. Fucoidan is an acidic polysaccharide with various biological activities. Our study showed that the transepithelial electrical resistance (TEER) value could reach 600 Ω·cm2 on the fourth day after the addition of fucoidan and puromycin, which met the applicable standards of the model (>500 Ω). Moreover, the alkaline phosphatase (AKP) activity, fluorescein sodium transmittance, and cell morphology of this model all met the requirements of model establishment. Fucoidan did not affect the absorption of macromolecular proteins and drugs. The results indicate that fucoidan can be applied to establish the Caco-2 model and can shorten the model establishment period to 5 days.

Absorption and Transport Characteristics and Mechanisms of Carnosic Acid

Simple Summary

Carnosic acid (CA), a phenolic diterpenoid mainly found in rosemary and sage, has been reported to possess various health-beneficial activities. However, detailed information about the absorption characteristics and mechanisms of CA and its tissue distribution still remains unclear. It has been well-recognized that the absorption, transport, and metabolism of dietary bioactive compounds are closely related to their biological functions. Herein, a mouse study and Caco-2 cell monolayer model of the intestinal epithelial barrier were used to understand the absorption and transport characteristics of CA. First, we determined the tissue distribution of CA in mice following oral gavage at a physiologically relevant dose. We found that CA was bioavailable systemically and present locally in the digestive tract, especially in the cecum and colon. Next, in Caco-2 cell monolayers, CA exhibited a moderate permeability and was subjected to mild efflux. Moreover, the apparent permeability coefficient of CA transported across Caco-2 cell monolayers was significantly changed when the inhibitors of specific active transporter and passive diffusion were added, suggesting that the absorption and transport of CA involved both passive and active transportation. The present study is an important first step towards understanding the absorption, transport, and metabolic mechanisms of CA.

Abstract

Carnosic acid (CA) is a phenolic diterpenoid mainly found in rosemary and sage. CA has been reported to possess health-beneficial effects in various experimental settings. Herein, a mouse experiment and Caco-2 single-cell model were used to understand the absorption and transport characteristics of CA. First, we determined the tissue distribution of CA in mice, following an oral gavage at a physiologically relevant dose. We found that CA was bioavailable systemically and present locally in the digestive tract, especially in the cecum and colon. Next, we thought to characterize the absorption and transport of CA in the Caco-2 cell monolayer model of the intestinal epithelial barrier. In the Caco-2 cell model, CA exhibited a moderate permeability and was subjected to a mild efflux. Moreover, the apparent permeability coefficient (P_app) of CA transported across Caco-2 cell monolayers was significantly changed when the inhibitors of specific active transporter and passive diffusion were added to cells, suggesting that the absorption and transport of CA involved both passive and active transportation. The present study is an important first step towards understanding the absorption, transport, and metabolic mechanisms of CA. This could provide the scientific basis for developing CA-containing functional foods or dietary supplements with improved bioavailability.

Assessing Intestinal Health. In Vitro and Ex vivo Gut Barrier Models of Farm Animals: Benefits and Limitations

Animal performance is determined by the functionality and health of the gastrointestinal tract (GIT). Complex mechanisms and interactions are involved in the regulation of GIT functionality and health. The understanding of these relationships could be crucial for developing strategies to improve animal production yields. The concept of "gut health" is not well defined, but this concept has begun to play a very important role in the field of animal science. However, a clear definition of GIT health and the means by which to measure it are lacking. In vitro and ex vivo models can facilitate these studies, creating well-controlled and repeatable conditions to understand how to improve animal gut health. Over the years, several models have been developed and used to study the beneficial or pathogenic relationships between the GIT and the external environment. This review aims to describe the most commonly used animals' in vitro or ex vivo models and techniques that are useful for better understanding the intestinal health of production animals, elucidating their benefits and limitations.

Re-Use of Caco-2 Monolayers in Permeability Assays-Validation Regarding Cell Monolayer Integrity

Caco-2 monolayers are a common in vitro model used to evaluate human intestinal absorption. The reference protocol requires 21 days post-seeding to establish a stable and confluent cell monolayer, which is used in a single permeability assay during the period of monolayer stability (up to day 30). In this work, we characterize variations in the tightness of the cell monolayer over the stable time interval and evaluate the conditions required for their re-use in permeability assays. The monolayer integrity was assessed through TEER measurements and permeability of the paracellular marker Lucifer Yellow (LY), complemented with nuclei and ZO-1 staining for morphological studies and the presence of tight junctions. Over 150 permeability assays were performed, which showed that manipulation of the cell monolayer in the permeability assay may contribute significantly to the flux of LY, leading to P_app values that are dependent on the sampling duration. The assay also leads to a small decrease in the cell monolayer TEER, which is fully recovered when cell monolayers are incubated with culture media for two full days. When this procedure is followed, the cell monolayers may be used for permeability assays on days 22, 25, and 28, triplicating the throughput of this important assay.

An overview of in vitro, ex vivo and in vivo models for studying the transport of drugs across intestinal barriers

Oral administration is the most commonly used route for drug delivery owing to its cost-effectiveness, ease of administration, and high patient compliance. However, the absorption of orally delivered compounds is a complex process that greatly depends on the interplay between the characteristics of the drug/formulation and the gastrointestinal tract. In this contribution, we review the different preclinical models (in vitro, ex vivo and in vivo) from their development to application for studying the transport of drugs across intestinal barriers. This review also discusses the advantages and disadvantages of each model. Furthermore, the authors have reviewed the selection and validation of these models and how the limitations of the models can be addressed in future investigations. The correlation and predictability of the intestinal transport data from the preclinical models and human data are also explored. With the increasing popularity and prevalence of orally delivered drugs/formulations, sophisticated preclinical models with higher predictive capacity for absorption of oral formulations used in clinical studies will be needed.

Hydrogel co-networks of gelatine methacrylate and poly(ethylene glycol) diacrylate sustain 3D functional in vitro models of intestinal mucosa

Mounting evidence supports the importance of the intestinal epithelial barrier and its permeability both in physiological and pathological conditions. Conventional in vitro models to evaluate intestinal permeability rely on the formation of tightly packed epithelial monolayers grown on hard substrates. These two-dimensional models lack the cellular and mechanical components of the non-epithelial compartment of the intestinal barrier, the stroma, which are key contributors to the barrier permeability in vivo. Thus, advanced in vitro models approaching the in vivo tissue composition are fundamental to improve precision in drug absorption predictions, to provide a better understanding of the intestinal biology, and to faithfully represent related diseases. Here, we generate photo-crosslinked gelatine methacrylate (GelMA)-poly(ethylene glycol) diacrylate (PEGDA) hydrogel co-networks that provide the required mechanical and biochemical features to mimic both the epithelial and stromal compartments of the intestinal mucosa, i.e. they are soft, cell adhesive and cell-loading friendly, and suitable for long-term culturing. We show that fibroblasts can be embedded in the GelMA-PEGDA hydrogels while epithelial cells can grow on top to form a mature epithelial monolayer that exhibits barrier properties which closely mimic those of the intestinal barrier in vivo, as shown by the physiologically relevant transepithelial electrical resistance (TEER) and permeability values. The presence of fibroblasts in the artificial stroma compartment accelerates the formation of the epithelial monolayer and boosts the recovery of the epithelial integrity upon temporary barrier disruption, demonstrating that our system is capable of successfully reproducing the interaction between different cellular compartments. As such, our hydrogel co-networks offer a technologically simple yet sophisticated approach to produce functional three-dimensional (3D) in vitro models of epithelial barriers with epithelial and stromal cells arranged in a spatially relevant manner and near-physiological functionality.

Investigating the Bioaccessibility and Bioavailability of Cadmium in a Cooked Rice Food Matrix by Using an 11-Day Rapid Caco-2/HT-29 Co-culture Cell Model Combined with an In Vitro Digestion Model

Investigating the bioaccessibility and bioavailability of Cd based on real contaminated cooked rice matrixes helps establish an accurate risk assessment method and effectively reduce the digestion and absorption of Cd. An 11-day in vitro rapid Caco-2/HT-29 co-culture cell model was used to establish and evaluate the simulation of the absorption and transport of Cd in the small intestine with a 70:30 Caco-2/HT-29 co-culture ratio and 1.0 mmol L^-1 butyric acid as a differentiation inducer. The bioaccessibility and bioavailability of Cd in cooked rice were studied using the cell model combined with an in vitro digestion model. The bioaccessibility of Cd of each of the three cooked rice samples was significantly higher in the gastric phase (59.04-80.23%) than in the gastrointestinal phase (37.14-52.93%). Despite the extension of the digestion time of the gastrointestinal phase, no significant difference was found among the time points. Results demonstrated that the amount of undigested residue, not the level of Cd contamination, significantly contributed to the bioaccessibility of Cd, which was affected by pH or ion. The absorption rate of Cd (25.08% ± 3.05%) was greater than the values obtained using the pure Caco-2 cell models. The bioavailability of Cd (8.29% ± 1.95%) was almost similar to that of Zn²⁺ (6.66% ± 1.41%) in the cooked rice matrix, indicating that the intestinal epithelium expressed a strong absorptive capacity of Cd during the absorption of essential metallic elements. The 11-day rapid Caco-2/HT-29 co-culture cell model combined with the in vitro digestion model was an efficient tool for studying the bioaccessibility and bioavailability of Cd or other substances in a food matrix to further investigate mechanistic steps and screen a broad set of food matrix factors.

Maltase-glucoamylase inhibition potency and cytotoxicity of pyrimidine-fused compounds: An in silico and in vitro approach

The prevalence of diabetes mellitus has been incremented in the current century and the need for novel therapeutic compounds to treat this disease has been significantly increased. One of the most promising approaches is to inhibit intestinal alpha glucosidases. Based on our previous studies, four pyrimidine-fused heterocycles (PFH) were selected as they revealed satisfactory inhibitory action against mammalian α-glucosidase. The interaction of these compounds with both active domains of human maltase-glucoamylase (MGAM) and their effect on human Caco-2 cell line were investigated. The docking assessments suggested that binding properties of these ligands were almost similar to that of acarbose by establishing hydrogen bonds especially with Tyr1251 and Arg526 in both C-terminal and N-terminal MGAM, respectively. Also, these compounds indicated a stronger affinity for C-terminal of MGAM. L2 and L4 made tightly complexes with both terminals of MGAM which in turn revealed the importance of introducing pyrimidine scaffold and its hinge compartment. The results of molecular dynamics simulation analyses confirmed the docking data and showed deep penetration of L2 and L4 into the active site of MGAM. Based on cell cytotoxicity assessments, no significant cell death induction was observed. Hence, these functional MGAM inhibitors might be considered as new potential therapeutic compounds in treatment of diabetes and its complications.

Advances and Current Challenges in Intestinal in vitro Model Engineering: A Digest

The physiological environment of the intestine is characterized by its variegated composition, numerous functions and unique dynamic conditions, making it challenging to recreate the organ in vitro. This review outlines the requirements for engineering physiologically relevant intestinal in vitro models, mainly focusing on the importance of the mechano-structural cues that are often neglected in classic cell culture systems. More precisely: the topography, motility and flow present in the intestinal epithelium. After defining quantitative descriptors for these features, we describe the current state of the art, citing relevant approaches used to address one (or more) of the elements in question, pursuing a progressive conceptual construction of an "ideal" biomimetic intestinal model. The review concludes with a critical assessment of the currently available methods to summarize the important features of the intestinal tissue in the light of their different applications.

Real-time cellular impedance monitoring and imaging of biological barriers in a dual-flow membrane bioreactor

The generation of physiologically relevant in-vitro models of biological barriers can play a key role in understanding human diseases and in the development of more predictive methods for assessing toxicity and drug or nutrient absorption. Here, we present an advanced cell culture system able to mimic the dynamic environment of biological barriers while monitoring cell behaviour through real-time impedance measurements and imaging. It consists of a fluidic device with an apical and a basal flow compartment separated by a semi-permeable membrane. The main features of the device are the integration of sensing through transepithelial electrical impedance (TEEI) measurements and transparent windows for optical monitoring within a dual flow system. Caco-2 cells were cultured in the TEEI bioreactor under both flow and static conditions. Although no differences in the expression of peripheral actin and occludin were visible, the cells in dynamic conditions developed higher impedance values at low frequencies, indicative of a higher paracellular electrical impedance with respect to the static cultures. TEEI measurements at high frequency also enabled monitoring monolayer formation, which can be correlated with the observation of an RC behaviour in the impedance spectra. In particular, the cells subject to flow showed accelerated barrier formation and increased vitality with respect to the static controls, again highlighting the importance of dynamic conditions for epithelial cells.

Human Cells Grown With or Without Substitutes for Fetal Bovine Serum

Safety concerns over cell-derived pharmaceutical products being manufactured in supplements of fetal bovine serum (FBS) have ignited pleas to replace FBS. Herein, four newly marketed alternatives to FBS were compared: a xeno-free product called Cell-Ess®, a human platelet lysate marketed as GroPro®, and two mixtures of adult bovine serum varying in their proportions of neonatal growth factors, called Liporo® and FetalGro®. An endothelial cell line (C2BBe1) and a neuronal cell line (SHSY5Y) near confluency in media with 10% FBS were selectively scraped and taken through a 25-day step-wise algorithm to replace FBS, and another human endothelial cell line (HRA-19) was studied to replicate C2BBe1. Cells were stained, counted, and compared for viability, migration, and spheroids. The C2BBe1 and HRA-19 cell lines failed to proliferate in 10% Cell-Ess® but grew in 10% GroPro® or 10% FetalGro® reasonably well compared to reference 10% FBS. With SH-SY5Y, only FetalGro® approached FBS's efficacy. These were all inferior to 11 different branded lots of FBS (positive controls), but five days into switching just amongst the FBS brands, 4 of 11 supported less proliferation than reference FBS in endothelial HRA-19 (p < 0.004). Moreover, neurospheres were enriched in two branded lots of FBS and FetalGro® (each p < 0.004), neurospheres being an unwanted phenotype for any neuronal cell application. Because platelet-derived GroPro® stood out amongst the non-FBS growth supplements to allow proliferation without inducing spheroids, it seems the best (mindful that the cells still grew slower in it compared to FBS). While no perfect replacement was found amongst the alternatives to FBS, the algorithm for switching should be useful in future testing of new alternatives to FBS as the need arises to switch from FBS and expand pharmaceutical products with safety for human use.

Cell cultures in drug discovery and development: The need of reliable in vitro-in vivo extrapolation for pharmacodynamics and pharmacokinetics assessment

For ethical and cost-related reasons, use of animals for the assessment of mode of action, metabolism and/or toxicity of new drug candidates has been increasingly scrutinized in research and industrial applications. Implementation of the 3 "Rs"¹; rule (Reduction, Replacement, Refinement) through development of in silico or in vitro assays has become an essential element of risk assessment. Physiologically based pharmacokinetic (PBPK²) modeling is the most potent in silico tool used for extrapolation of pharmacokinetic parameters to animal or human models from results obtained in vitro. Although, many types of in vitro assays are conducted during drug development, use of cell cultures is the most reliable one. Two-dimensional (2D) cell cultures have been a part of drug development for many years. Nowadays, their role is decreasing in favor of three-dimensional (3D) cell cultures and co-cultures. 3D cultures exhibit protein expression patterns and intercellular junctions that are closer to in vivo states in comparison to classical monolayer cultures. Co-cultures allow for examinations of the mutual influence of different cell lines. However, the complexity and high costs of co-cultures and 3D equipment exclude such methods from high-throughput screening (HTS).³In vitro absorption, distribution, metabolism, and excretion assessment, as well as drug-drug interaction (DDI), are usually performed with the use of various cell culture based assays. Progress in in silico and in vitro methods can lead to better in vitro-in vivo extrapolation (IVIVE⁴) outcomes and have a potential to contribute towards a significant reduction in the number of laboratory animals needed for drug research. As such, concentrated efforts need to be spent towards the development of an HTS in vitro platform with satisfactory IVIVE features.