Inhibition of mitogen-activated protein kinase kinase, DNA methyltransferase, and transforming growth factor-β promotes differentiation of human induced pluripotent stem cells into enterocytes

Toward Xeno-Free Differentiation of Human Induced Pluripotent Stem Cell-Derived Small Intestinal Epithelial Cells

The small intestinal epithelium has an important role in nutrition, but also in drug absorption and metabolism. There are a few two-dimensional (2D) patient-derived induced pluripotent stem cell (iPSC)-based intestinal models enabling easy evaluation of transcellular transport. It is known that animal-derived components induce variation in the experimental outcomes. Therefore, we aimed to refine the differentiation protocol by using animal-free components. More specifically, we compared maturation of 2D-cultured iPCSs toward small intestinal epithelial cells when cultured either with or without serum, and either on Geltrex or on animal-free, recombinant laminin-based substrata. Differentiation status was characterized by qPCR, immunofluorescence imaging, and functionality assays. Our data suggest that differentiation toward definitive endoderm is more efficient without serum. Both collagen- and recombinant laminin-based coating supported differentiation of definitive endoderm, posterior definitive endoderm, and small intestinal epithelial cells from iPS-cells equally well. Small intestinal epithelial cells differentiated on recombinant laminin exhibited slightly more enterocyte specific cellular functionality than cells differentiated on Geltrex. Our data suggest that functional small intestinal epithelial cells can be generated from iPSCs in serum-free method on xeno-free substrata. This method is easily converted to an entirely xeno-free method.

Usefulness of human jejunal spheroid-derived differentiated intestinal epithelial cells for the prediction of intestinal drug absorption in humans

This study aimed to demonstrate the usefulness of human jejunal spheroid-derived differentiated intestinal epithelial cells as a novel in vitro model for clarifying the impact of intestinal drug-metabolizing enzymes and transporters on the intestinal absorption of substrate drugs in humans. Three-dimensional human intestinal spheroids were successfully established from surgical human jejunal specimens and expanded for a long period using L-WRN-conditioned medium, which contains Wnt3a, R-spondin 3, and noggin. The mRNA expression levels of intestinal pharmacokinetics-related genes in the human jejunal spheroid-derived differentiated intestinal epithelial cells were drastically increased over a 5-day period after seeding compared with those in human jejunal spheroids and were approximately the same as those in human jejunal tissue over a culture period of at least 13 days. Activities of typical drug-metabolizing enzymes (cytochrome P450 [CYP] 3A, CYP2C9, uridine 5'-diphospho-glucuronosyltransferase 1A, and carboxylesterase 2) and uptake/efflux transporters (peptide transporter 1/SLC15A1, P-glycoprotein, and breast cancer resistance protein) in the differentiated cells were confirmed. Furthermore, intestinal availability (Fg) values estimated from the apical-to-basolateral permeation clearance across cell monolayer showed a good correlation with the in vivo Fg values in humans for five CYP3A substrate drugs (Fg range, 0.35-0.98). In conclusion, the functions of major intestinal drug-metabolizing enzymes and transporters could be maintained in human jejunal spheroid-derived differentiated intestinal epithelial cells. This model would be useful for the quantitative evaluation of the impact of intestinal drug-metabolizing enzymes and transporters on the intestinal absorption of substrate drugs in humans. Significance Statement Limited information is available regarding the quantitative prediction of the impact of drug-metabolizing enzymes and transporters on the human intestinal absorption of substrates using in vitro assays with differentiated cells derived from human intestinal spheroids/organoids. We confirmed the functions of typical drug-metabolizing enzymes and transporters in human jejunal spheroid-derived differentiated intestinal epithelial cells and demonstrated that Fg values estimated from apical-to-basolateral permeation clearance across cell monolayers showed a good correlation with in vivo human Fg values for CYP3A substrate drugs.

Quantitative prediction of pharmacokinetic properties of drugs in humans: Recent advance in in vitro models to predict the impact of efflux transporters in the small intestine and blood-brain barrier

Efflux transport systems are essential to suppress the absorption of xenobiotics from the intestinal lumen and protect the critical tissues at the blood-tissue barriers, such as the blood-brain barrier. The function of drug efflux transport is dominated by various transporters. Accumulated clinical evidences have revealed that genetic variations of the transporters, together with coadministered drugs, affect the expression and/or function of transporters and subsequently the pharmacokinetics of substrate drugs. Thus, in the preclinical stage of drug development, quantitative prediction of the impact of efflux transporters as well as that of uptake transporters and metabolic enzymes on the pharmacokinetics of drugs in humans has been performed using various in vitro experimental tools. Various kinds of human-derived cell systems can be applied to the precise prediction of drug transport in humans. Mathematical modeling consisting of each intrinsic metabolic or transport process enables us to understand the disposition of drugs both at the organ level and at the level of the whole body by integrating a variety of experimental results into model parameters. This review focuses on the role of efflux transporters in the intestinal absorption and brain distribution of drugs, in addition to recent advances in predictive tools and methodologies.

Pharmacokinetic functions of human induced pluripotent stem cell-derived small intestinal epithelial cells

To develop a novel intestinal drug absorption system using intestinal epithelial cells derived from human induced pluripotent stem (iPS) cells, the cells must possess sufficient pharmacokinetic functions. However, the CYP3A4/5 activities of human iPS cell-derived small intestinal epithelial cells prepared using conventional differentiation methods is low. Further, studies of the CYP3A4/5 activities of human iPS-derived and primary small intestinal cells are not available. To fill this gap in our knowledge, here we used forskolin to develop a new differentiation protocol that activates adenosine monophosphate signaling. mRNA expressions of human iPS cell-derived small intestinal epithelial cells, such as small intestine markers, drug-metabolizing enzymes, and drug transporters, were comparable to or greater than those of the adult small intestine. The activities of CYP3A4/5 in the differentiated cells were equal to those of human primary small intestinal cells. The differentiated cells had P-glycoprotein and PEPT1 activities equivalent to those of Caco-2 cells. Differentiated cells were superior to Caco-2 cells for predicting the membrane permeability of drugs that were absorbed through a paracellular pathway and via drug transporters. In summary, here we produced human iPS cell-derived small intestinal epithelial cells with CYP3A4/5 activities equivalent to those of human primary small intestinal cells.

Repair and regeneration of small intestine: A review of current engineering approaches

The small intestine (SI) is difficult to regenerate or reconstruct due to its complex structure and functions. Recent developments in stem cell research, advanced engineering technologies, and regenerative medicine strategies bring new hope of solving clinical problems of the SI. This review will first summarize the structure, function, development, cell types, and matrix components of the SI. Then, the major cell sources for SI regeneration are introduced, and state-of-the-art biofabrication technologies for generating engineered SI tissues or models are overviewed. Furthermore, in vitro models and in vivo transplantation, based on intestinal organoids and tissue engineering, are highlighted. Finally, current challenges and future perspectives are discussed to help direct future applications for SI repair and regeneration.

[Generation of human iPS cell-derived hepatocytes and enterocytes for application to drug disposition studies]

In drug disposition, the liver and small intestine are very important as tissues involving in drug metabolism, absorption, and excretion. Thus, in drug development studies, it is necessary to evaluate the pharmacokinetics in these tissues accurately including the contributions of drug-metabolizing enzymes and drug transporters. Currently, all kinds of evaluation systems have been used for the pharmacokinetic prediction; however, there are some issues in these systems. Therefore, the researches for the development of human induced pluripotent stem (iPS) cell-derived hepatocytes and enterocytes, as novel systems besides existing ones, are being advanced. Because human iPS cells have abilities of pluripotency and almost infinite proliferation, it is thought to be possible to stably provide the high-quality cells that have similar characteristics to human normal tissue cells by using human iPS cells. In this review, we describe current status of differentiation studies of human iPS cell-derived hepatocytes and enterocytes and the functional characteristics of these cells centered on pharmacokinetic functions.

[Development of an In Vitro System for Evaluating Intestinal Drug Disposition Using Human Induced Pluripotent Stem Cell-Derived Intestinal Epithelial Cells]

　Tissues of the small intestine are crucial to understanding drug disposition because these tissues regulate the bioavailability of drugs. However, no evaluation system is currently available for precise and comprehensive analysis of intestinal pharmacokinetics. To address this, functional intestinal epithelial cells were generated from human induced pluripotent stem (iPS) cells for use in pharmacokinetic studies. An improved intestinal differentiation method was established by screening a variety of small molecule compounds against cells during differentiation. The mRNA expression levels of intestinal markers, drug transporters, and CYP3A4 were found to increase following treatment with compounds that act as inhibitors of mitogen-activated protein kinase, DNA methyltransferase, and transforming growth factor-β. Therefore, we inferred that these compounds enhanced differentiation into intestinal epithelial cells. The differentiated intestinal epithelial cells in the presence of these compounds possessed drug-metabolizing enzyme activities, such as those of CYPs, UDP-glucuronosyltransferase, and sulfotransferase. In addition, these cells had the ability to induce CYP3A4 in the presence of 1α,25-dihydroxyvitamin D₃. The differentiated intestinal epithelial cells seeded on cell culture inserts formed loose-tight junctions, similar to those in the human small intestine, rather than Caco-2 cells. The cells exhibited polarity, such as apical and basal sides. We also demonstrated that the uptake and efflux transport activities in the cells occurred via peptide transporter and breast cancer resistance protein, respectively. Taken together, it was suggested that human iPS cell-derived intestinal epithelial cells are pharmacokinetically functional, and represent a promising model system for pharmacokinetic studies of drug candidates.

Cyclic AMP Signaling Promotes the Differentiation of Human Induced Pluripotent Stem Cells into Intestinal Epithelial Cells

To develop a novel in vitro system for predicting intestinal drug absorption using human induced pluripotent stem (iPS) cell-derived intestinal epithelial cells, the cells need to have sufficient drug-metabolizing enzyme and drug transporter activities. We found that cyclic adenosine monophosphate (cAMP) signaling plays an important role in the differentiation of human iPS cells into intestinal epithelial cells. In this study, we aimed to demonstrate the effects of signaling activation in the intestinal differentiation of human iPS cells and the pharmacokinetic characteristics of human iPS cell-derived intestinal epithelial cells. Human iPS cells were differentiated into intestinal stem cells using activin A and fibroblast growth factor 2. Subsequently, the intestinal stem cells were maturated into intestinal epithelial cells by treatment with 8-bromo-cyclic adenosine monophosphate (8-Br-cAMP) and 3-isobutyl-1-methylxanthine (IBMX), which activate cAMP signaling. The expression levels of intestinal markers and pharmacokinetics-related genes in the differentiated cells were markedly increased by using 8-Br-cAMP and IBMX. In the cells differentiated with the compound we observed cytochrome P450 (CYP) 3A4 inducibility via pregnane X receptor and vitamin D receptor. The metabolic activities of CYP2C9, CYP2C19, CYP2D6, CYP3A4/5, and UDP-glucuronosyltransferase, which are expressed in the human small intestine, were also markedly increased. Furthermore, uptake of glycylsarcosine via peptide transporter 1 was markedly increased. The cells differentiated with the compounds also had drug transporter activities via organic anion transporters and P-glycoprotein. This study is the first to report that the activation of cAMP signaling promotes differentiation of human iPS cell-derived intestinal epithelial cells.

iPSC-Derived Enterocyte-like Cells for Drug Absorption and Metabolism Studies

Intestinal cell models have been widely studied and used to evaluate absorption and metabolism of drugs in the small intestine, constituting valuable tools as a first approach to evaluate the behavior of new drugs. However, such cell models might not be able to fully predict the absorption mechanisms and metabolic pathways of the tested compounds. In recent years, induced pluripotent stem cells (iPSCs) differentiated into enterocyte-like cells have been proposed as more biorelevant intestinal models. In this review, we describe mechanisms underlying the differentiation of iPSCs into enterocyte-like cells, appraise the usefulness of these cells in tridimensional intestinal models, and discuss their suitability to be used in the future for drug screening.

Milk's Role as an Epigenetic Regulator in Health and Disease

It is the intention of this review to characterize milk's role as an epigenetic regulator in health and disease. Based on translational research, we identify milk as a major epigenetic modulator of gene expression of the milk recipient. Milk is presented as an epigenetic "doping system" of mammalian development. Milk exosome-derived micro-ribonucleic acids (miRNAs) that target DNA methyltransferases are implicated to play the key role in the upregulation of developmental genes such as FTO, INS, and IGF1. In contrast to miRNA-deficient infant formula, breastfeeding via physiological miRNA transfer provides the appropriate signals for adequate epigenetic programming of the newborn infant. Whereas breastfeeding is restricted to the lactation period, continued consumption of cow's milk results in persistent epigenetic upregulation of genes critically involved in the development of diseases of civilization such as diabesity, neurodegeneration, and cancer. We hypothesize that the same miRNAs that epigenetically increase lactation, upregulate gene expression of the milk recipient via milk-derived miRNAs. It is of critical concern that persistent consumption of pasteurized cow's milk contaminates the human food chain with bovine miRNAs, that are identical to their human analogs. Commercial interest to enhance dairy lactation performance may further increase the epigenetic miRNA burden for the milk consumer.