Keratinocyte serum-free medium maintains long-term liver gene expression and function in cultured rat hepatocytes by preventing the loss of liver-enriched transcription factors

Characterization of Correction Factors to Enable Assessment of Clinical Risk from In Vitro CYP3A4 Induction Data and Basic Drug-Drug Interaction Models

Background and Objective

Induction of drug-metabolizing enzymes can lead to drug-drug interactions (DDIs); therefore, early assessment is often conducted. Previous reports focused on true positive cytochrome P450 3A (CYP3A) inducers leaving a gap in translation for in vitro inducers which do not manifest in clinical induction. The goal herein was to expand the in vitro induction dataset by including true negative clinical inducers to identify a correction factor to basic DDI models, which reduces false positives without impacting false negatives.

Methods

True negative clinical inducers were identified through a literature search, in vitro induction parameters were generated in three human hepatocyte donors, and the performance of basic induction models proposed by regulatory agencies, concentration producing twofold induction (F2), basic static model (R3) and relative induction score (RIS), was used to characterize clinical induction risk.

Results

The data demonstrated the importance of correcting for in vitro binding and metabolism to derive induction parameters. The aggregate analysis indicates that the RIS with a positive cut-off of < 0.7-fold area under the curve ratio (AUCR) provides the best quantitative prediction. Additionally, correction factors of ten and two times the unbound peak plasma concentration at steady state (C_max,ss,u) can be confidently used to identify true positive inducers when referenced against the concentration resulting in twofold increase in messenger ribonucleic acid (mRNA) or using the R3 equation, respectively.

Conclusions

These iterative improvements, which reduce the number of false positives, could aid regulatory recommendations and limit unnecessary clinical explorations into CYP3A induction.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s13318-022-00763-y.

Analysis of soluble factors in conditioned media derived from primary cultures of cirrhotic liver of biliary atresia

Biliary atresia (BA) is a rare and serious liver disease in newborn infants. Previously, we reported that non-parenchymal cell (NPC) fractions from cirrhotic liver of BA may contain hepatic stem/progenitor cells in primary culture of NPC fractions. In this study, NPC fractions were subjected to primary or passage culture and found that clusters of hepatocyte-like cells appear even without adding hepatocyte growth factor (HGF) to the culture medium, but not in their passage culture used as a control. Based on these findings, conditioned media (CMs) were collected and soluble factors in the CMs were analyzed in order to elucidate the mechanism of the appearance of hepatocyte-like cells or their clusters. A large amount of active HGF consisting of α and β chains was detected in CMs derived from primary culture, but not in CMs from passage culture, as determined by western blot analysis, bone morphogenetic protein (BMP)-4, oncostatin M (OSM), and transforming growth factor (TGF)-β1 were not detected in any of the CMs. The number of hepatocyte-like cells in primary culture tended to decrease following treatment with the HGF receptor c-Met inhibitor, SU11274 in a dose-dependent manner. Furthermore, the clusters of hepatocyte-like cells tended to increase in size and number when freshly isolated NPC fractions were cultured in the presence of 10% of CMs collected after 3-4 wk of primary culture. In conclusion, these findings indicate that CMs derived from primary culture of NPC fractions of BA liver contain a large amount of active HGF, which may activate hepatic stem/progenitor cells and promote the appearance of hepatocyte-like cells or their clusters through HGF/c-Met signaling. The present study would lead to cell therapy using the patient's own cells for the treatment of BA.

Efficient programming of human mesenchymal stem cell-derived hepatocytes by epigenetic regulations

BACKGROUND AND AIM

In view of its unique properties of detoxification and involvement of metabolic and biochemical functions, in vitro hepatocyte culture serves as a valuable material for drug screening and mechanistic analysis for pathology of liver diseases. The restriction of rapid de-differentiation and inaccessibility of human hepatocytes from routine clinical procedure, however, limits its use.

METHODS

To address this issue, the effort to direct human mesenchymal stem cells (hMSCs) into hepatocytes using a modified protocol was proposed. With the additional treatment of histone deacetylase inhibitor (HDACi) and DNA methyltransferase inhibitor (DNMTi), in vitro hMSC-derived hepatocytes were cultivated and their hepatic characteristics were examined.

RESULTS

By using a modified protocol, it was shown that Trichostatin A and 5-aza-2-deoxycitidine protected differentiating cells from death and could sufficiently trigger a wide range of liver-specific markers as well as liver functions including albumin production, glycogen storage, and urea cycle in hMSC-derived hepatocytes. The increased mRNA expression for hepatitis C virus (HCV) entry including CD81, Occludin, LDL receptor, and scavenger receptor class B type I in hMSC-derived hepatocytes was also detected, implying its potential to be utilized as an in vitro model to analyze dynamic HCV infection.

CONCLUSIONS

The present study successfully established a protocol to direct hMSCs into hepatocyte-like cells suggesting the beneficial impact to apply HDACi and DNMTi as potent modulators for hMSCs to liver differentiation.

Hnf4α is a key gene that can generate columnar metaplasia in oesophageal epithelium

Barrett's metaplasia is the only known morphological precursor to oesophageal adenocarcinoma and is characterized by replacement of stratified squamous epithelium by columnar epithelium. The cell of origin is uncertain and the molecular mechanisms responsible for the change in cellular phenotype are poorly understood. We therefore explored the role of two transcription factors, Cdx2 and HNF4α in the conversion using primary organ cultures. Biopsy samples from cases of human Barrett's metaplasia were analysed for the presence of CDX2 and HNF4α. A new organ culture system for adult murine oesophagus is described. Using this, Cdx2 and HNF4α were ectopically expressed by adenoviral infection. The phenotype following infection was determined by a combination of PCR, immunohistochemical and morphological analyses. We demonstrate the expression of CDX2 and HNF4α in human biopsy samples. Our oesophageal organ culture system expressed markers characteristic of the normal SSQE: p63, K14, K4 and loricrin. Ectopic expression of HNF4α, but not of Cdx2 induced expression of Tff3, villin, K8 and E-cadherin. HNF4α is sufficient to induce a columnar-like phenotype in adult mouse oesophageal epithelium and is present in the human condition. These data suggest that induction of HNF4α is a key early step in the formation of Barrett's metaplasia and are consistent with an origin of Barrett's metaplasia from the oesophageal epithelium.

Hepatocyte-ductal transdifferentiation is mediated by reciprocal repression of SOX9 and C/EBPα

Primary hepatocytes rapidly dedifferentiate when cultured in vitro. We have studied the mechanism of hepatocyte dedifferentiation by using two culture media: one that maintains hepatocytes in a differentiated state and another that allows dedifferentiation. We show that dedifferentiation involves partial transformation of hepatocytes into cells that resemble biliary epithelial cells. Lineage labeling and time-lapse filming confirm that the dedifferentiated cells are derived from hepatocytes and not from contaminating ductal or fibroblastic cells in the original culture. Furthermore, we establish that the conversion of hepatocytes to biliary-like cells is regulated by mutual antagonism of CCAAT/enhancer binding protein alpha (C/EBPα) and SOX9, which have opposing effects on the expression of hepatocyte and ductal genes. Thus, hepatocyte dedifferentiation induces the biliary gene expression program by alleviating C/EBPα-mediated repression of Sox9. We propose that reciprocal antagonism of C/EBPα and SOX9 also operates in the formation of hepatocytes and biliary ducts from hepatoblasts during normal embryonic development. These data demonstrate that reprogramming of differentiated cells can be used to model the acquisition and maintenance of cell fate in vivo.

Stable insulin-secreting ducts formed by reprogramming of cells in the liver using a three-gene cocktail and a PPAR agonist

With the long-term aim of developing a new type of therapy for diabetes, we have investigated the reprogramming of liver cells in normal mice toward a pancreatic phenotype using the gene combination Pdx1, Ngn3, MafA. CD1 mice were rendered diabetic with streptozotocin and given a single dose of Ad-PNM, an adenoviral vector containing all three genes. Ad-PNM induced hepatocytes of the liver to produce insulin, and the blood glucose became normalized. But over several weeks, the insulin-positive cells were lost and the blood glucose rose back to diabetic levels. Simultaneous administration of a peroxisome-proliferator-activated receptor agonist, WY14643, caused remission of diabetes at a lower dose of Ad-PNM and also caused the appearance of a population of insulin-secreting ductal structures in the liver. The insulin-positive ducts were stable and were able to relieve diabetes in the long term. We show that the effect of WY14643 is associated with the promotion of cell division of the ductal cells, which may increase their susceptibility to being reprogrammed toward a beta cell fate.

Human fetal keratocytes have multipotent characteristics in the developing avian embryo

The human cornea contains stem cells that can be induced to express markers consistent with multipotency in cell culture; however, there have been no studies demonstrating that human corneal keratocytes are multipotent. The objective of this study is to examine the potential of human fetal keratocytes (HFKs) to differentiate into neural crest-derived tissues when challenged in an embryonic environment. HFKs were injected bilaterally into the cranial mesenchyme adjacent to the neural tube and the periocular mesenchyme in chick embryos at embryonic days 1.5 and 3, respectively. The injected keratocytes were detected by immunofluorescence using the human cell-specific marker, HuNu. HuNu-positive keratocytes injected along the neural crest pathway were localized adjacent to HNK-1-positive migratory host neural crest cells and in the cardiac cushion mesenchyme. The HuNu-positive cells transformed into neural crest derivatives such as smooth muscle in cranial blood vessels, stromal keratocytes, and corneal endothelium. However, they failed to form neurons despite their presence in the condensing trigeminal ganglion. These results show that HFKs retain the ability to differentiate into some neural crest-derived tissues. Their ability to respond to embryonic cues and generate corneal endothelium and stromal keratocytes provides a basis for understanding the feasibility of creating specialized cells for possible use in regenerative medicine.

Direct lineage conversion of terminally differentiated hepatocytes to functional neurons

Several recent studies have showed that mouse and human fibroblasts can be directly reprogrammed into induced neuronal (iN) cells, bypassing a pluripotent intermediate state. However, fibroblasts represent heterogeneous mesenchymal progenitor cells that potentially contain neural crest lineages, and the cell of origin remained undefined. This raises the fundamental question of whether lineage reprogramming is possible between cell types derived from different germ layers. Here, we demonstrate that terminally differentiated hepatocytes can be directly converted into functional iN cells. Importantly, single-cell and genome-wide expression analyses showed that fibroblast- and hepatocyte-derived iN cells not only induced a neuronal transcriptional program, but also silenced their donor transcriptome. The remaining donor signature decreased over time and could not support functional hepatocyte properties. Thus, the reprogramming factors lead to a binary lineage switch decision rather than an induction of hybrid phenotypes, but iN cells retain a small but detectable epigenetic memory of their donor cells.

Hydrogel embedding of precision-cut liver slices in a microfluidic device improves drug metabolic activity

A microfluidic-based biochip made of poly-(dimethylsiloxane) was recently reported for the first time by us for the incubation of precision-cut liver slices (PCLS). In this system, PCLS are continuously exposed to flow, to keep the incubation environment stable over time. Slice behavior in the biochip was compared with that of slices incubated in well plates, and verified for 24 h. The goal of the present study was to extend this incubation time. The viability and metabolic activity of precision-cut rat liver slices cultured in our novel microflow system was examined for 72 h. Slices were incubated for 1, 24, 48, and 72 h, and tested for viability (enzyme leakage (lactate dehydrogenase)) and metabolic activity (7-hydroxycoumarin (phase II) and 7-ethoxycoumarin (phase I and II)). Results show that liver slices retained a higher viability in the biochip when embedded in a hydrogel (Matrigel) over 72 h. This embedding prevented the slices from attaching to the upper polycarbonate surface in the microchamber, which occurred during prolonged (>24 h) incubation in the absence of hydrogel. Phase II metabolism was completely retained in hydrogel-embedded slices when medium supplemented with dexamethasone, insulin, and calf serum was used. However, phase I metabolism was significantly decreased with respect to the initial values in gel-embedded slices with medium supplements. Slices were still able to produce phase I metabolites after 72 h, but at only about ∼10% of the initial value. The same decrease in metabolic rate was observed in slices incubated in well plates, indicating that this decrease is due to the slices and medium rather than the incubation system. In conclusion, the biochip model was significantly improved by embedding slices in Matrigel and using proper medium supplements. This is important for in vitro testing of drug metabolism, drug-drug interactions, and (chronic) toxicity.

Isolation and culture of adult mouse hepatocytes

The liver performs a multitude of functions including the regulation of carbohydrate, fat, and protein metabolism, the detoxification of endo- and xenobiotics, and the synthesis and secretion of plasma proteins and bile. Isolated hepatocytes constitute a useful technique for studying liver function in an in vitro setting. Here we describe a method for the isolation of hepatocytes from adult mouse liver. The principle of the method is the two-step collagenase perfusion technique which involves sequential perfusion of the liver with ethylenediaminetetraacetic acid and collagenase. Following isolation, the cells can either be used for short-term studies or, alternatively, maintained in culture for prolonged periods to study long-term changes in gene expression. The protocol for mouse hepatocyte isolation may be applied to both normal and transgenic mice.

Inhibition of Hes1 activity in gall bladder epithelial cells promotes insulin expression and glucose responsiveness

The biliary system has a close developmental relationship with the pancreas, evidenced by the natural occurrence of small numbers of biliary-derived beta-cells in the biliary system and by the replacement of biliary epithelium with pancreatic tissue in mice lacking the transcription factor Hes1. In normal pancreatic development, Hes1 is known to repress endocrine cell formation. Here we show that glucose-responsive insulin secretion can be induced in biliary epithelial cells when activity of the transcription factor Hes1 is antagonised. We describe a new culture system for adult murine gall bladder epithelial cells (GBECs), free from fibroblast contamination. We show that Hes1 is expressed both in adult murine gall bladder and in cultured GBECs. We have created a new dominant negative Hes1 (DeltaHes1) by removal of the DNA-binding domain, and show that it antagonises Hes1 function in vivo. When DeltaHes1 is introduced into the GBEC it causes expression of insulin RNA and protein. Furthermore, it confers upon the cells the ability to secrete insulin following exposure to increased external glucose. GBEC cultures are induced to express a wider range of mature beta cell markers when co-transduced with DeltaHes1 and the pancreatic transcription factor Pdx1. Introduction of DeltaHes1 and Pdx1 can therefore initiate a partial respecification of phenotype from biliary epithelial cell towards the pancreatic beta cell.

N-Acetyl-D-glucosamine oligosaccharides induce mucin secretion from colonic tissue and induce differentiation of human keratinocytes

Chitin oligosaccharides (DP2, DP3, DP4, DP5 and DP7) were investigated for their effects on epithelial cells and tissue (skin keratinocytes in-vitro and ex-vivo, and gastrointestinal epithelial membranes ex-vivo). Oligomers DP2, DP3 and DP5 at 10 μg mL−1 significantly stimulated the mitochondrial activity of cultured keratinocytes in-vitro (primary cells and HaCaT cell line), with highest activity observed for the pentamer (150% of untreated control). The effects were dose dependent. This higher energy status of primary cells was triggered into a higher differentiation status, as determined by the early and late differentiation markers keratins K1/K10 and involucrin, respectively. In contrast, increased mitogenic cell proliferation was not induced by the oligosaccharides. Toxic effects on keratinocytes were absent. Additionally for the first time a mucin-stimulating effect of chitin oligosaccharides DP3 and DP5 was observed in an ex-vivo model based on intestinal epithelial mucosa tissue. Mucin secretion was time dependent, leading to the secretion of polymers comparable to those normally secreted under physiological conditions. Mucin induction was observed from colonic tissue isolated from humans and pigs. Also, porcine stomach mucosa was stimulated by DP5, while ileum tissue reacted to only a minor extent. Potential developments towards products with wound-healing capacity and activity against chronic bowel disease are discussed.

Hepatocyte differentiation

Increasingly, research suggests that for certain systems, animal models are insufficient for human toxicology testing. The development of robust, in vitro models of human toxicity is required to decrease our dependence on potentially misleading in vivo animal studies. A critical development in human toxicology testing is the use of human primary hepatocytes to model processes that occur in the intact liver. However, in order to serve as an appropriate model, primary hepatocytes must be maintained in such a way that they persist in their differentiated state. While many hepatocyte culture methods exist, the two-dimensional collagen "sandwich" system combined with a serum-free medium, supplemented with physiological glucocorticoid concentrations, appears to robustly maintain hepatocyte character. Studies in rat and human hepatocytes have shown that when cultured under these conditions, hepatocytes maintain many markers of differentiation including morphology, expression of plasma proteins, hepatic nuclear factors, phase I and II metabolic enzymes. Functionally, these culture conditions also preserve hepatic stress response pathways, such as the SAPK and MAPK pathways, as well as prototypical xenobiotic induction responses. This chapter will briefly review culture methodologies but will primarily focus on hallmark hepatocyte structural, expression and functional markers that characterize the differentiation status of the hepatocyte.

Serum-free collagen sandwich cultures of adult rat hepatocytes maintain liver-like properties long term: a valuable model for in vitro toxicity and drug-drug interaction studies

Cultures of primary hepatocytes from various species, including human, are used in several applications during pre-clinical drug development. Their use is however limited by cell survival and conservation of liver-specific functions in vitro. The differentiation status of hepatocytes in culture strongly depends on medium formulation and the extracellular matrix environment. We incubated primary rat hepatocytes for 10 days on collagen monolayer and in collagen sandwich cultures with or without serum. Restoration of polygonal cell shape and formation of functional bile canaliculi-like structures was stable only in serum-free sandwich cultures. Variations in general cell viability, as judged by the cellular ATP content, LDH release or apoptosis, were less pronounced between alternative cultures. The intracellular glutathione content was preserved close to in vivo levels especially in serum-free sandwich cultures. Basal activities of cytochrome P450 enzymes (P450) varied strongly between cultures. There was a minor effect on CYP1A but CYP2B activity was only detectable in the serum-free sandwich culture after 3 days and beyond. CYP2C activity was slightly elevated in both sandwich cultures, whereas CYP3A showed increased levels in both serum-free cultures. Inducibility of these P450s was fully maintained over time in serum-free collagen sandwich only. Gene expression was largely constant over time in serum-free sandwich cultures that was closest to liver. This liver-like property was supported by protein profiling results. Taken together, the serum-free collagen sandwich culture of primary rat hepatocytes maintained liver-like features over 10 days and is therefore a suitable model for long-term toxicity and drug-drug interaction studies.