Simultaneous in vitro measurement of intestinal tissue permeability and transepithelial electrical resistance (TEER) using Sweetana-Grass diffusion cells

Possible Regulation of P-Glycoprotein Function by Adrenergic Agonists II: Study with Isolated Rat Jejunal Sheets and Caco-2 Cell monolayers

To clarify the regulation of drug absorption by the enteric nervous system, we investigated how adrenergic agonists (adrenaline (ADR), clonidine (CLO), dobutamine (DOB)) and dibutyryl cAMP (DBcAMP) affected P-glycoprotein (P-gp) function by utilizing isolated rat jejunal sheets and Caco-2 cell monolayers. ADR and CLO significantly decreased the secretory transport (Papptotal) of rhodamine-123 and tended to decrease the transport via P-gp (PappP-gp) and passive transport (Papppassive). In contrast, DBcAMP significantly increased and DOB tended to increase Papptotal and both tended to increase PappP-gpand Papppassive. Changes in P-gp expression on brush border membrane by adrenergic agonists and DBcAMP were significantly correlated with PappP-gp, while P-gp expression was not changed in whole cell homogenates, suggesting that the trafficking of P-gp would be responsible for its functional changes. Papppassive was inversely correlated with transmucosal or transepithelial electrical resistance, indicating that adrenergic agonists affected the paracellular permeability. Adrenergic agonists also changed cAMP levels, which were significantly correlated with PappP-gp. Furthermore, protein kinase A (PKA) or PKC inhibitor significantly decreased PappP-gp in Caco-2 cell monolayers, suggesting that they would partly contribute to the changes in P-gp activity. In conclusion, adrenergic agonists regulated P-gp function and paracellular permeability, which would be caused via adrenoceptor stimulation.

Effects of Digestion, Cell Culture Media, and Mucous on the Physical Properties, Cellular Effects, and Translocation of Polystyrene and Polymethacrylate Nanoparticles

The discovery of plastic and metal nanoparticles in organisms, foods, and beverages has generated numerous studies on the effects of these particles on the barrier cells and their subsequent absorption into the body. Following ingestion, nanoparticles travel down the gastrointestinal tract (GIT), and their physicochemical characteristics change in response to the change in proteins and pH during their digestion. We measured the translocation of digested nanoparticles across a co-culture monolayer of Caco-2 and various combinations (1:9, 5:5, and 9:1) of HT29-MTX-E12. The in vitro model of the intestine was used to determine the translocation of digested 20 nm polymethacrylate (PMA) particles and the accompanying monolayer barrier effects after a 72 h exposure. The in vitro digestion increased the agglomeration and hydrodynamic diameters and decreased the surface charge of the nanoparticles. For NH2-functionalized polymethacrylate nanoparticles (PMA-NH2), the diameters increased from 57 nm (water) to 3800 nm (media), or 2660 nm (chyme). These nanoparticles compromised the integrity of the monolayer (trans-epithelial electrical resistance, Lucifer yellow translocation) and translocated across all the cell ratio configurations. Digestion can have a large effect on nanoparticle agglomeration and surface charge. Excess mucous was not seen as a barrier to the translocation of PMA-NH2.

Openable artificial intestinal tract device integrated with a permeable filter for evaluating drug permeation through cells

Organs-on-chips using cultured cells have been developed and applied for evaluating in vitro biological phenomena. We previously reported an openable artificial intestinal tract system, as an in vitro model of the small intestine, for in vitro drug screening. The intestinal tract device could be transformed using an integrated artificial muscle actuator. An initial flat state was suitable for cell culture, and the transformed tubular structure was used as a fluidic channel for perfusion tests. The previously developed intestinal tract system could be used to evaluate drug absorption by cells through perfusion testing. This study presents an improved artificial intestinal tract system for analysis of drug permeation, in addition to absorption. Permeable filters were integrated into the intestinal tract device. Integration of additional filters into the design of the existing artificial muscle actuator was accomplished by considering device performance and available filter locations. Filter permeability was evaluated by perfusion testing. MDCK-II cells were cultured on the device and visually and electrically evaluated. The openable device, equipped with new functions for further pharmacokinetic analysis, could perform and evaluate drug disposition using cultured cells. We anticipate that the improved, openable organ-on-a-chip device system will contribute to advances in in vitro drug screening technology.

In vitro and ex vivo experimental models for evaluation of intranasal systemic drug delivery as well as direct nose-to-brain drug delivery

The intranasal route of administration provides a noninvasive method to deliver drugs into the systemic circulation and/or directly into the brain. Direct nose-to-brain drug delivery offers the possibility to treat central nervous system diseases more effectively, as it can evade the blood-brain barrier. In vitro and ex vivo intranasal models provide a means to investigate physiological and pharmaceutical factors that could play a role in drug delivery across the nasal epithelium as well as to determine the mechanisms involved in drug absorption from the nose. The development and implementation of cost-effective pharmacokinetic models for intranasal drug delivery with good in vitro-in vivo correlation can accelerate pharmaceutical drug product development and improve economic and ecological aspects by reducing the time and costs spent on animal studies. Special considerations should be made with regard to the purpose of the in vitro/ex vivo study, namely, whether it is intended to predict systemic or brain delivery, source and site of tissue or cell sampling, viability window of selected model, and the experimental setup of diffusion chambers. The type of model implemented should suit the relevant needs and requirements of the project, researcher, and interlaboratory. This review aims to provide an overview of in vitro and ex vivo models that have been developed to study intranasal and direct nose-to-brain drug delivery.

Gastrointestinal Permeation Enhancers for the Development of Oral Peptide Pharmaceuticals

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

In vivo, ex vivo and in vitro assessment of buccal permeation of drugs from delivery systems

Introduction: Buccal mucosa has been described as an attractive site for local and systemic drug delivery, owing its accessibility, safety, and excellent blood supply. The absorption of drugs through buccal mucosa has been assessed by in vivo, ex vivo and in vitro permeability studies, using animal and cell-based models with close resemblance to the human buccal mucosa.Areas covered: This paper focuses on the current in vivo, ex vivo and in vitro permeability studies to analyze the absorption of compounds of interest through buccal mucosa, as well as their advantages and limitations in the preclinical studies of the drugs absorption profiles. The techniques for preparation and preservation of the animal buccal tissue are also discussed to evaluate their interference in the integrity and permeability of the tissues.Expert opinion: Overall, the permeability studies have been useful to evaluate the drugs absorption and to clarify the mechanism of transport of drugs across human buccal mucosa, as well as to explain the enhancement of permeability provided by certain dosage forms. Currently, several researchers have demonstrated particular interest in ex vivo permeability studies, due to their effectiveness in the evaluation of drug absorption and low costs in the acquisition of buccal mucosa samples.

In vitro and in vivo models for the study of oral delivery of nanoparticles

Oral delivery is an attractive route to deliver therapeutics via nanoparticles due to its ease of administration and patient compliance. This review discusses laboratory techniques for studying oral delivery of nanoparticles, which offer protection of cargo through the gastrointestinal tract. Some of the difficulties in modeling oral delivery include the harsh acidic environment, variable pH, and the tight monolayer of endothelial cells present throughout the gastrointestinal tract. The use of in vitro techniques including the Transwell ® system, simulated gastric/intestinal fluid, and diffusion chambers addresses these challenges. When studying effects after oral delivery in vivo, bioimaging of nanoparticle biodistribution using radioactive markers has been popular. Functional assays such as immune response and systemic protein concentration analysis can further define the merits of the oral delivery systems. As biologics become increasingly more important in chronic therapies, nanoparticle-mediated oral delivery will assume greater prominence, and more sophisticated in vitro and in vivo models will be required.

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

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

Comparative assessment of three in vitro exposure methods for combustion toxicity

A comparative assessment of three approaches for the use of human cells in vitro to investigate combustion toxicity was conducted. These included one indirect and two direct (passive and dynamic) exposure methods. The indirect method used an impinger system in which culture medium was used to trap the toxicants, whilst the direct exposure involved the use of a Horizontal Harvard Navicyte Chamber at the air/liquid interface. The cytotoxic effects of thermal decomposition products were assessed using the MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) assay (Promega) on a selection of human cells including: HepG2, A549 and skin fibroblasts. A small scale laboratory fire test using a vertical tube furnace was designed for the generation of combustion products. Polymethyl methacrylate (PMMA) was selected as a model polymer to study the cytotoxic effects of combustion products. NOAEC (no observable adverse effect concentration), IC10 (10% inhibitory concentration), IC50 (50% inhibitory concentration) and TLC (total lethal concentration) values were determined from dose response curves. Assessment using the NRU (neutral red uptake) and ATP (adenosine triphosphate) assays on human lung derived cells (A549) was also undertaken. Comparison between in vitro cytotoxicity results against published toxicity data for PMMA combustion and predicted LC50 (50% lethal concentration) values calculated from identified compounds using GCMS (gas chromatography mass spectrometry) was determined. The results suggested that the indirect exposure method did not appear to simulate closely exposure via inhalation, whilst exposure at the air/liquid interface by using the dynamic method proved to be a more representative method of human inhalation. This exposure method may be a potential system for in vitro cytotoxicity testing in combustion toxicity.

Evaluation of human intestinal absorption data and subsequent derivation of a quantitative structure–activity relationship (QSAR) with the Abraham descriptors

The human intestinal absorption of 241 drugs was evaluated. Three main methods were used to determine the human intestinal absorption: bioavailability, percentage of urinary excretion of drug-related material following oral administration, and the ratio of cumulative urinary excretion of drug-related material following oral and intravenous administration. The general solvation equation developed by Abraham's group was used to model the human intestinal absorption data of 169 drugs we considered to have reliable data. The model contains five Abraham descriptors calculated by the ABSOLV program. The results show that Abraham descriptors can successfully predict human intestinal absorption if the human absorption data is carefully classified based on solubility and administration dose to humans.

The effect of cysteine and 2,4-dinitrophenol on heme and nonheme absorption in a rat intestinal model

Previous studies have showed that purified heme iron forms insoluble polymers that are poorly absorbed. The presence of peptides and of amino acids maintaining heme iron in a soluble form could improve its bioavailability. The digestive uptake and transfer of a concentrated hydrolysate of heme peptides (HPH) and of iron gluconate (Gluc) at 100 µM were compared in vitro in a Ussing chamber. The effects of an enhancing amino acid (L-cysteine) on the uptake and transfer of both forms were assessed. An inhibitor of the oxidative phosphorylation (2,4-dinitrophenol; DNP) was used to differentiate the active and passive mechanisms of the absorption. The mucosal uptake (%Tot) and enterocyte transfer (%S) of the two sources of iron did not differ. DNP significantly reduced %Tot and %S of both forms. Cysteine significantly enhanced %Tot and %S of HPH and Gluc, partly corrected the inhibition exerted by DNP on %Tot of HPH and %S of both forms, and fully restored %Tot of Gluc. In presence of peptides produced by globin hydrolysis, the absorption of hemoglobin iron was efficient; it was mostly energy dependent and, therefore, should have occurred by a regulated transcellular pathway. Cysteine enhanced the passive uptake of iron and the passive processes involved in the enterocyte transfer of the common pool made of both sources (heme and nonheme) of iron. These results showed that heme iron can be purified and concentrated without impairing its digestive absorption, provided it remains in presence of peptides or amino acids.

Prediction of human intestinal absorption of drug compounds from molecular structure

The absorption of a drug compound through the human intestinal cell lining is an important property for potential drug candidates. Measuring this property, however, can be costly and time-consuming. The use of quantitative structure-property relationships (QSPRs) to estimate percent human intestinal absorption (%HIA) is an attractive alternative to experimental measurements. A data set of 86 drug and drug-like compounds with measured values of %HIA taken from the literature was used to develop and test a QSPR mode. The compounds were encoded with calculated molecular structure descriptors. A nonlinear computational neural network model was developed by using the genetic algorithm with a neural network fitness evaluator. The calculated %HIA (cHIA) model performs wells, with root-mean-square (rms) errors of 9.4%HIA units for the training set, 19.7%HIA units for the cross-validation (CV) set, and 16.0%HIA units for the external prediction set.

Absorption-enhancing effects of sodium caprate and palmitoyl carnitine in rat and human colons

We examined the enhancing action of sodium caprate and palmitoylcarnitine on the permeability of fluorescein isothiocyanate dextran 4000 as a paracellular permeant compound in isolated rat and human colon samples using the Ussing-type chamber method. In the absence of an enhancer, the permeation clearance of fluorescein isothiocyanate dextran 4000 was not significantly different in the rat and human colons, but the electric membrane resistance was smaller in the rat colon than in the human colon. Sodium caprate and palmitoylcarnitine increased permeation clearance and decreased electric membrane resistance in both types of colonic membrane, showing that the rat colon can be used as a model of the human colon for studies of enhancer effects. A calmodulin antagonist significantly inhibited the action of sodium caprate in both colonic membranes. However, it tended to promote the effects of palmitoylcarnitine on permeation clearance and electric membrane resistance. These results suggest that sodium caprate induces the contraction of the perijunctional actomyosin ring to widen the tight junction and that the mechanism of palmitoylcarnitine is different from that of sodium caprate in the human colon, as reported previously for Caco-2 cell monolayers.

Absorption-enhancing mechanism of EDTA, caprate, and decanoylcarnitine in Caco-2 cells

The mechanism of paracellular expansion by absorption enhancers, e.g., EDTA, sodium caprate (C10), and decanoylcarnitine (DC), was studied, the focus being on the process of actin microfilament contraction in the tight junction. The effects of various inhibitors such as KN-62 (a specific inhibitor of Ca2+/calmodulin dependent protein kinase), H7 (a protein kinase C (PKC) inhibitor), and W7 (a calmodulin antagonist) were examined on the paracellular expansion by the enhancers in Caco-2 cells. From the experimental results, the following mechanisms were suggested. EDTA activates PKC by depletion of extracellular calcium via chelation resulting in expansion of the paracellular route. C10 increases the intracellular calcium level by an interaction with the cell membrane independent of cell polarity resulting in contraction with actin microfilament. DC interacts specifically with the apical membrane to increase the intracellular calcium level, but the mechanistic details subsequent to the increase of calcium are not clear.

Oral delivery of sodium cromolyn: preliminary studies in vivo and in vitro

PURPOSE

Herein we report the discovery of a group of derivatized alpha-amino acids that increase the oral bioavailability of sodium cromolyn.

METHODS

We prepared three N-acylated alpha-amino acids and used these compounds to demonstrate the oral delivery of cromolyn in an in vivo rat model. In vitro experiments, including permeation studies and near infrared spectroscopy, were also performed to initiate an understanding of the mechanism by which these compounds facilitate cromolyn oral delivery.

RESULTS

Following oral administration to rats of solutions containing a combination of cromolyn and the delivery agent, significant systemic plasma concentrations of the drug were detected. In vitro studies suggest that absorption of the drug across the gastrointestinal membrane is a passive process.

CONCLUSION

The absolute oral bioavailability of sodium cromolyn in the rat model is estimated to be approximately 5%. Preliminary mechanistic studies suggest that a complex of the cromolyn/delivery agent facilitates permeation across/through the membrane.

Enhancement of calcium transport in the Caco-2 cell monolayer model

The overall objective of this research was to identify enhancers of calcium transport using an in-vitro Caco-2 cell monolayer model. The enhancers studied were medium-chain triglycerides (MCT) and acylcarnitines (AC). The extent of cell damage associated with the use of these enhancers was determined by monitoring the release of cellular lactate dehydrogenase (LDH). The effect of chain-length and concentration dependence of these agents on enhancement were also determined. The effects of ACs were found to be superior to those of MCTs. However, the ACs elicited a greater release of LDH than the MCTs. The possible mechanisms of enhancer-mediated increase in calcium transport and the potential significance of this study with regard to the prevention of osteoporosis are discussed.