Maintenance of drug metabolism and transport functions in human precision-cut liver slices during prolonged incubation for 5 days

Human precision-cut cystic duct and gallbladder slices: a novel method for studying cholangiopathies

Background and aims

Precision-cut tissue slices (PCTS) are widely used as an ex vivo culture tissue culture technique to study pathogeneses of diseases and drug activities in organs in vitro. A novel application of the PCTS model may be in the field of translational research into cholangiopathies such as biliary atresia. Therefore, the aim of this study was to apply the precision-cut slice technique to human bile duct and gallbladder tissue.

Methods

Cystic duct and gallbladder tissue derived from patients undergoing a cholecystectomy were collected, preserved and used for preparation of precision-cut cystic duct slices (PCCDS) and precision-cut gallbladder slices (PCGS). The PCCDS and PCGS were prepared using a mechanical tissue slicer and subsequently incubated for 24 and 48 h respectively in William's Medium E (WME) culture medium. Viability was assessed based on ATP/protein content and tissue morphology [hematoxylin and eosin (H&E) staining].

Results

It was shown that viability, assessed by the ATP/protein content and morphology, of the PCCDS (n = 8) and PCGS (n = 8) could be maintained over the 24 and 48 h incubation period respectively. ATP/protein content of the PCCDS increased significantly from 0.58 ± 0.13 pmol/µg at 0 h to 2.4 ± 0.29 pmol/µg after 24 h incubation (P = .0003). A similar significant increase from 0.94 ± 0.22 pmol/µg at 0 h to 3.7 ± 0.41 pmol/µg after 24 h (P = .0005) and 4.2 ± 0.47 pmol/µg after 48 h (P = .0002) was observed in the PCGS. Morphological assessment of the PCCDS and PCGS showed viable tissue at 0 h and after 24 and 48 h incubation respectively.

Conclusion

This study is the first to report on the use of the PCTS model for human gallbladder and cystic duct tissue. PCCDS and PCGS remain viable for an incubation period of at least 24 h, which makes them suitable for research purposes in the field of cholangiopathies, including biliary atresia.

Mouse precision-cut liver slices as an ex vivo model to study drug-induced cholestasis

Drugs are often withdrawn from the market due to the manifestation of drug-induced liver injury (DILI) in patients. Drug-induced cholestasis (DIC), defined as obstruction of hepatic bile flow due to medication, is one form of DILI. Because DILI is idiosyncratic, and the resulting cholestasis complex, there is no suitable in vitro model for early DIC detection during drug development. Our goal was to develop a mouse precision-cut liver slice (mPCLS) model to study DIC and to assess cholestasis development using conventional molecular biology and analytical chemistry methods. Cholestasis was induced in mPCLS through a 48-h-incubation with three drugs known to induce cholestasis in humans, namely chlorpromazine (15, 20, and 30 µM), cyclosporin A (1, 3, and 6 µM) or glibenclamide (25, 50, and 65 µM). A bile-acid mixture (16 µM) that is physiologically representative of the human bile-acid pool was added to the incubation medium with drug, and results were compared to incubations with no added bile acids. Treatment of PCLS with cholestatic drugs increased the intracellular bile-acid concentration of deoxycholic acid and modulated bile-transporter genes. Chlorpromazine led to the most pronounced cholestasis in 48 h, observed as increased toxicity; decreased protein and gene expression of the bile salt export pump; increased gene expression of multidrug resistance-associated protein 4; and accumulation of intracellular bile acids. Moreover, chlorpromazine-induced cholestasis exhibited some transition into fibrosis, evidenced by increased gene expression of collagen 1A1 and heatshock protein 47. In conclusion, we demonstrate that mPCLS can be used to study human DIC onset and progression in a 48 h period. We thus propose this model is suited for other similar studies of human DIC.

Preclinical models of idiosyncratic drug-induced liver injury (iDILI): Moving towards prediction

Idiosyncratic drug-induced liver injury (iDILI) encompasses the unexpected harms that prescription and non-prescription drugs, herbal and dietary supplements can cause to the liver. iDILI remains a major public health problem and a major cause of drug attrition. Given the lack of biomarkers for iDILI prediction, diagnosis and prognosis, searching new models to predict and study mechanisms of iDILI is necessary. One of the major limitations of iDILI preclinical assessment has been the lack of correlation between the markers of hepatotoxicity in animal toxicological studies and clinically significant iDILI. Thus, major advances in the understanding of iDILI susceptibility and pathogenesis have come from the study of well-phenotyped iDILI patients. However, there are many gaps for explaining all the complexity of iDILI susceptibility and mechanisms. Therefore, there is a need to optimize preclinical human in vitro models to reduce the risk of iDILI during drug development. Here, the current experimental models and the future directions in iDILI modelling are thoroughly discussed, focusing on the human cellular models available to study the pathophysiological mechanisms of the disease and the most used in vivo animal iDILI models. We also comment about in silico approaches and the increasing relevance of patient-derived cellular models.

Intracellular ATP Concentration and Implication for Cellular Evolution

Crystalline lens and striated muscle exist at opposite ends of the metabolic spectrum. Lens is a metabolically quiescent tissue, whereas striated muscle is a mechanically dynamic tissue with high-energy requirements, yet both tissues contain millimolar levels of ATP (>2.3 mM), far exceeding their underlying metabolic needs. We explored intracellular concentrations of ATP across multiple cells, tissues, species, and domains to provide context for interpreting lens/striated muscle data. Our database revealed that high intracellular ATP concentrations are ubiquitous across diverse life forms including species existing from the Precambrian Era, suggesting an ancient highly conserved role for ATP, independent of its widely accepted view as primarily "metabolic currency". Our findings reinforce suggestions that the primordial function of ATP was non-metabolic in nature, serving instead to prevent protein aggregation.

Organotypic-liver slide culture systems to explore the role of extracellular vesicles in pancreatic cancer metastatic behavior and guide new therapeutic approaches

Introduction: Recent studies suggested that extracellular vesicles (EVs) play a role both in the metastatic niche formation and in the progression of several tumors, including pancreatic cancer. In particular, the effects of EVs on metastasis should be studied in model systems that take into account both the tumor cells and the metastatic site/tumor microenvironment. Studies with labeled EVs or EV-secreting cells in ex vivo models will reflect the physiological and pathological functions of EVs. The organotypic-tissue slide culture systems can fulfill such a role.Areas covered: This review provides an overview of available organotypic-culture slide systems. We specifically focus on the assay system of liver culture-slides in combination with pancreatic tumors, which can be modulated to test the efficacy of new therapeutic approaches.Expert opinion: The intercellular exchange of EVs has emerged as a biologically relevant phenomenon to drive cancer metastasis. However, further models need to be developed to better elucidate the functional roles of EVs. The use of novel organotypic slide culture systems provides the opportunity to explore the role of EVs in the metastatic behavior of pancreatic cancer, decreasing the use of costly and cumbersome organoid or animal models.

Best Practices and Progress in Precision-Cut Liver Slice Cultures

Thirty-five years ago, precision-cut liver slices (PCLS) were described as a promising tool and were expected to become the standard in vitro model to study liver disease as they tick off all characteristics of a good in vitro model. In contrast to most in vitro models, PCLS retain the complex 3D liver structures found in vivo, including cell–cell and cell–matrix interactions, and therefore should constitute the most reliable tool to model and to investigate pathways underlying chronic liver disease in vitro. Nevertheless, the biggest disadvantage of the model is the initiation of a procedure-induced fibrotic response. In this review, we describe the parameters and potential of PCLS cultures and discuss whether the initially described limitations and pitfalls have been overcome. We summarize the latest advances in PCLS research and critically evaluate PCLS use and progress since its invention in 1985.

Altered vitamin A metabolism in human liver slices corresponds to fibrogenesis

All-trans-retinoic acid (atRA), the active metabolite of vitamin A, has antifibrogenic properties in vitro and in animal models. Liver vitamin A homeostasis is maintained by cell-specific enzymatic activities including storage in hepatic stellate cells (HSCs), secretion into circulation from hepatocytes, and formation and clearance of atRA. During chronic liver injury, HSC activation is associated with a decrease in liver retinyl esters and retinol concentrations. atRA is synthesized through two enzymatic steps from retinol, but it is unknown if the loss of retinoid stores is associated with changes in atRA formation and which cell types contribute to the metabolic changes. The aim of this study was to determine if the vitamin A metabolic flux is perturbed in acute liver injury, and if changes in atRA concentrations are associated with HSC activation and collagen expression. At basal levels, HSC and Kupffer cells expressed key genes involved in vitamin A metabolism, whereas after acute liver injury, complex changes to the metabolic flux were observed in liver slices. These changes include a reproducible spike in atRA tissue concentrations, decreased retinyl ester and atRA formation rate, and time-dependent changes to the expression of metabolizing enzymes. Kinetic simulations suggested that oxidoreductases are important in determining retinoid metabolic flux after liver injury. These early changes precede HSC activation and upregulation of profibrogenic gene expression, which were inversely correlated with atRA tissue concentrations, suggesting that HSC and Kupffer cells are key cells involved in changes to vitamin A metabolic flux and signaling after liver injury. Study Highlights WHAT IS THE CURRENT KNOWLEDGE ON THE TOPIC? Vitamin A is metabolized in the liver for storage as retinyl esters in hepatic stellate cell (HSCs) or to all-trans-retinoic acid (atRA), an active metabolite with antifibrogenic properties. Following chronic liver injury, vitamin A metabolic flux is perturbed, and HSC activation leads to diminished retinoid stores. WHAT QUESTION DID THIS STUDY ADDRESS? Do changes in the expression of vitamin A metabolizing enzymes explain changes in atRA concentrations and the regulation of fibrosis following acute liver injury? WHAT DOES THIS STUDY ADD TO OUR KNOWLEDGE? In healthy liver, both HSC and Kupffer cells may mediate vitamin A homeostasis. Following acute liver injury, complex changes in metabolizing enzyme expression/activity alter the metabolic flux of retinoids, resulting in a transient peak in atRA concentrations. The atRA concentrations are inversely correlated with profibrogenic gene expression, HSC activation, and collagen deposition. HOW MIGHT THIS CHANGE CLINICAL PHARMACOLOGY OR TRANSLATIONAL SCIENCE? Improved understanding of altered vitamin A metabolic flux in acute liver injury may provide insight into cell-specific contributions to vitamin A loss and lead to novel interventions in liver fibrosis.

Alternative strategies in cardiac preclinical research and new clinical trial formats

An efficient and safe drug development process is crucial for the establishment of new drugs on the market aiming to increase quality of life and life-span of our patients. Despite technological advances in the past decade, successful launches of drug candidates per year remain low. We here give an overview about some of these advances and suggest improvements for implementation to boost preclinical and clinical drug development with a focus on the cardiovascular field. We highlight advantages and disadvantages of animal experimentation and thoroughly review alternatives in the field of three-dimensional cell culture as well as preclinical use of spheroids and organoids. Microfluidic devices and their potential as organ-on-a-chip systems, as well as the use of living animal and human cardiac tissues are additionally introduced. In the second part, we examine recent gold standard randomized clinical trials and present possible modifications to increase lead candidate throughput: adaptive designs, master protocols, and drug repurposing. In silico and N-of-1 trials have the potential to redefine clinical drug candidate evaluation. Finally, we briefly discuss clinical trial designs during pandemic times.

Nanoparticle-induced inflammation and fibrosis in ex vivo murine precision-cut liver slices and effects of nanoparticle exposure conditions

Chronic exposure and accumulation of persistent nanomaterials by cells have led to safety concerns on potential long-term effects induced by nanoparticles, including chronic inflammation and fibrosis. With this in mind, we used murine precision-cut liver tissue slices to test potential induction of inflammation and onset of fibrosis upon 72 h exposure to different nanomaterials (0–200 µg/ml). Tissue slices were chosen as an advanced ex vivo 3D model to better resemble the complexity of the in vivo tissue environment, with a focus on the liver where most nanomaterials accumulate. Effects on the onset of fibrosis and inflammation were investigated, with particular care in optimizing nanoparticle exposure conditions to tissue. Thus, we compared the effects induced on slices exposed to nanoparticles in the presence of excess free proteins (in situ), or after corona isolation. Slices exposed to daily-refreshed nanoparticle dispersions were used to test additional effects due to ageing of the dispersions. Exposure to amino-modified polystyrene nanoparticles in serum-free conditions led to strong inflammation, with stronger effects with daily-refreshed dispersions. Instead, no inflammation was observed when slices were exposed to the same nanoparticles in medium supplemented with serum to allow corona formation. Similarly, no clear signs of inflammation nor of onset of fibrosis were detected after exposure to silica, titania or carboxylated polystyrene in all conditions tested. Overall, these results show that liver slices can be used to test nanoparticle-induced inflammation in real tissue, and that the exposure conditions and ageing of the dispersions can strongly affect tissue responses to nanoparticles.

Application of In Vitro Metabolism Activation in High-Throughput Screening

In vitro methods which incorporate metabolic capability into the assays allow us to assess the activity of metabolites from their parent compounds. These methods can be applied into high-throughput screening (HTS) platforms, thereby increasing the speed to identify compounds that become active via the metabolism process. HTS was originally used in the pharmaceutical industry and now is also used in academic settings to evaluate biological activity and/or toxicity of chemicals. Although most chemicals are metabolized in our body, many HTS assays lack the capability to determine compound activity via metabolism. To overcome this problem, several in vitro metabolic methods have been applied to an HTS format. In this review, we describe in vitro metabolism methods and their application in HTS assays, as well as discuss the future perspectives of HTS with metabolic activity. Each in vitro metabolism method has advantages and disadvantages. For instance, the S9 mix has a full set of liver metabolic enzymes, but it displays high cytotoxicity in cell-based assays. In vitro metabolism requires liver fractions or the use of other metabolically capable systems, including primary hepatocytes or recombinant enzymes. Several newly developed in vitro metabolic methods, including HepaRG cells, three-dimensional (3D) cell models, and organ-on-a-chip technology, will also be discussed. These newly developed in vitro metabolism approaches offer significant progress in dissecting biological processes, developing drugs, and making toxicology studies quicker and more efficient.

Magnetic Nanomaterials in Chinese Medicine Chemical Composition Analysis and Drug Metabolism and Its Industry Prospect and Development Path Research

The paramagnetism and superparamagnetism of magnetic nanomaterials are very important for in vivo applications. The magnetic particles with paramagnetism or superparamagnetism can redistribute the magnetic particles after the magnetic field is withdrawn, which is widely used for the separation and purification of biomolecules. At the same time, superparamagnetic particles can also be used as MRI imaging contrast agent. Compared with Western medicine, traditional Chinese medicine is different from Western medicine in that it is originated from nature and has thousands of years of clinical efficacy. Therefore, we hope to elaborate the complex mechanism of traditional Chinese medicine through some modern technical means: through the establishment of relevant quality control system, Chinese medicine will be recognized and popularized in the international field. Therefore, this paper discusses the application of magnetic nanomaterials in the chemical composition analysis and drug metabolism of traditional Chinese medicine and its industrial prospect and development path. Firstly, the advantages of magnetic nanomaterials and the shortcomings of chemical composition analysis technology of traditional Chinese medicine are analyzed theoretically. Then, through the experimental simulation, the results show that, under the optimal conditions, the magnetic nanomaterials can be used to analyze the chemical composition of traditional Chinese medicine. The peak current and concentration of THP showed a good linear relationship in the range of 5.2 × 10−8 ∼ 2.1 × 10−5  mol/L, and the detection limit was 1.9 × 10−7  mol/L. Moreover, it showed effective results in repeatability, stability, and interference tests. Therefore, magnetic nanomaterials play an important role in the chemical composition analysis and drug metabolism of traditional Chinese medicine as well as its industrial prospect and development path.

Metabolism of cyclic phenones in rainbow trout in vitro assays

1. Cyclic phenones are chemicals of interest to the USEPA due to their potential for endocrine disruption to aquatic and terrestrial species.2. Prior to this report, there was very limited information addressing metabolism of cyclic phenones by fish species and the potential for estrogen receptor (ER) binding and vitellogenin (Vtg) gene activation by their metabolites.3. The main objectives of the current research were to characterize rainbow trout (rt) liver slice-mediated in vitro metabolism of model parent cyclic phenones exhibiting disparity between ER binding and ER-mediated Vtg gene induction, and to assess the metabolic competency of fish liver in vitro tests to help determine the chemical form (parent and/or metabolite) associated with the observed biological response.4. GC-MS, HPLC and LC-MS/MS technologies were applied to investigate the in vitro biotransformation of cyclobutyl phenyl ketone (CBP), benzophenone (DPK), cyclohexyl phenyl ketone (CPK) mostly in the absence of standards for metabolite characterization.5. It was concluded that estrogenic effects of the studied cyclic phenones are mediated by the parent chemical structure for DPK, but by active metabolites for CPK. A definitive interpretation was not possible for CBP and CBPOH (alcohol), although a contribution of both structures to gene induction is suspected.

Current insights in the complexities underlying drug-induced cholestasis

Drug-induced cholestasis (DIC) poses a major challenge to the pharmaceutical industry and regulatory agencies. It causes both drug attrition and post-approval withdrawal of drugs. DIC represents itself as an impaired secretion and flow of bile, leading to the pathological hepatic and/or systemic accumulation of bile acids (BAs) and their conjugate bile salts. Due to the high number of mechanisms underlying DIC, predicting a compound's cholestatic potential during early stages of drug development remains elusive. A profound understanding of the different molecular mechanisms of DIC is, therefore, of utmost importance. Although many knowledge gaps and caveats still exist, it is generally accepted that alterations of certain hepatobiliary membrane transporters and changes in hepatocellular morphology may cause DIC. Consequently, liver models, which represent most of these mechanisms, are valuable tools to predict human DIC. Some of these models, such as membrane-based in vitro models, are exceptionally well-suited to investigate specific mechanisms (i.e. transporter inhibition) of DIC, while others, such as liver slices, encompass all relevant biological processes and, therefore, offer a better representation of the in vivo situation. In the current review, we highlight the principal molecular mechanisms associated with DIC and offer an overview and critical appraisal of the different liver models that are currently being used to predict the cholestatic potential of drugs.

A Bioreactor Technology for Modeling Fibrosis in Human and Rodent Precision-Cut Liver Slices

Precision cut liver slices (PCLSs) retain the structure and cellular composition of the native liver and represent an improved system to study liver fibrosis compared to two-dimensional mono- or co-cultures. The aim of this study was to develop a bioreactor system to increase the healthy life span of PCLSs and model fibrogenesis. PCLSs were generated from normal rat or human liver, or fibrotic rat liver, and cultured in our bioreactor. PCLS function was quantified by albumin enzyme-linked immunosorbent assay (ELISA). Fibrosis was induced in PCLSs by transforming growth factor beta 1 (TGFβ1) and platelet-derived growth factor (PDGFββ) stimulation ± therapy. Fibrosis was assessed by gene expression, picrosirius red, and α-smooth muscle actin staining, hydroxyproline assay, and soluble ELISAs. Bioreactor-cultured PCLSs are viable, maintaining tissue structure, metabolic activity, and stable albumin secretion for up to 6 days under normoxic culture conditions. Conversely, standard static transwell-cultured PCLSs rapidly deteriorate, and albumin secretion is significantly impaired by 48 hours. TGFβ1/PDGFββ stimulation of rat or human PCLSs induced fibrogenic gene expression, release of extracellular matrix proteins, activation of hepatic myofibroblasts, and histological fibrosis. Fibrogenesis slowly progresses over 6 days in cultured fibrotic rat PCLSs without exogenous challenge. Activin receptor-like kinase 5 (Alk5) inhibitor (Alk5i), nintedanib, and obeticholic acid therapy limited fibrogenesis in TGFβ1/PDGFββ-stimulated PCLSs, and Alk5i blunted progression of fibrosis in fibrotic PCLS. Conclusion: We describe a bioreactor technology that maintains functional PCLS cultures for 6 days. Bioreactor-cultured PCLSs can be successfully used to model fibrogenesis and demonstrate efficacy of antifibrotic therapies.

The Selection and Validation of Reference Genes for mRNA and microRNA Expression Studies in Human Liver Slices Using RT-qPCR

The selection of a suitable combination of reference genes (RGs) for data normalization is a crucial step for obtaining reliable and reproducible results from transcriptional response analysis using a reverse transcription-quantitative polymerase chain reaction. This is especially so if a three-dimensional multicellular model prepared from liver tissues originating from biologically diverse human individuals is used. The mRNA and miRNA RGs stability were studied in thirty-five human liver tissue samples and twelve precision-cut human liver slices (PCLS) treated for 24 h with dimethyl sulfoxide (controls) and PCLS treated with β-naphthoflavone (10 µM) or rifampicin (10 µM) as cytochrome P450 (CYP) inducers. Validation of RGs was performed by an expression analysis of CYP3A4 and CYP1A2 on rifampicin and β-naphthoflavone induction, respectively. Regarding mRNA, the best combination of RGs for the controls was YWHAZ and B2M, while YWHAZ and ACTB were selected for the liver samples and treated PCLS. Stability of all candidate miRNA RGs was comparable or better than that of generally used short non-coding RNA U6. The best combination for the control PCLS was miR-16-5p and miR-152-3p, in contrast to the miR-16-5b and miR-23b-3p selected for the treated PCLS. Our results showed that the candidate RGs were rather stable, especially for miRNA in human PCLS.

Precision-Cut Tissue Slices (PCTS) from the digestive gland of the Mediterranean mussel Mytilus galloprovincialis: An ex vivo approach for molecular and cellular responses in marine invertebrates

The precision-cut tissue slices (PCTS) represent a largely used biological model in mammalian research. This ex vivo approach offers the main advantages of in vitro systems, while maintaining the natural architecture of the tissue. The use of PCTS in toxicological research has been proposed for investigating the cellular effects of xenobiotics or bioactive compounds mostly in mammalian models. Their application is increasing also in marine organisms, but still limited to fish. This work validates the use of PCTS in an invertebrate species, the Mediterranean mussel Mytilus galloprovincialis. Intact tissue slices of different thicknesses (300, 350 and 400 μm) were successfully obtained from the digestive gland. The slices maintained the histological integrity and the viability after 6 h and 24 h incubation in culture medium, with some differences depending on the thickness. The enzymatic activities and mRNA levels of catalase and glutathione S-transferase, chosen as model biological endpoints, were measured until 24 h incubation, revealing the functionality of such systems. This work demonstrates the suitability of mussel PCTS for investigating molecular and cellular responses in ecotoxicological research.

Growth factors of stem cell niche extend the life-span of precision-cut intestinal slices in culture: A proof-of-concept study

Precision-cut intestinal slices (PCIS) is an ex vivo culture technique that found its applications in toxicology, drug transport and drug metabolism testing, as well as in fibrosis research. The main limiting factor of PCIS as experimental model is the relatively short viability of tissue slices. Here, we describe a strategy for extending the life-span of PCIS during culture using medium that is routinely used for growing intestinal organoids. Mouse and rat PCIS cultured in standard medium progressively showed low ATP/protein content and severe tissue degradation, indicating loss of tissue viability. In turn, organoid medium, containing epithelial growth factor (EGF), Noggin and R-spondin, maintained significantly higher ATP/protein levels and better preserved intestinal architecture of mouse PCIS at 96 h. In contrast, organoid medium that additionally contained Wnt, had a clear positive effect on the ATP content of rat PCIS during 24 h of culture, but not on slice histomorphology. Our proof-of-concept study provides early evidence that employing organoid medium for PCIS culture improved tissue viability during extended incubation. Enabling lasting PCIS cultures will greatly widen their range of applications in predicting long-term intestinal toxicity of xenobiotics and elucidating their mechanism of action, among others.

Mechanisms and in vitro models of drug-induced cholestasis

Cholestasis underlies one of the major manifestations of drug-induced liver injury. Drug-induced cholestatic liver toxicity is a complex process, as it can be triggered by a variety of factors that induce 2 types of biological responses, namely a deteriorative response, caused by bile acid accumulation, and an adaptive response, aimed at removing the accumulated bile acids. Several key events in both types of responses have been characterized in the past few years. In parallel, many efforts have focused on the development and further optimization of experimental cell culture models to predict the occurrence of drug-induced cholestatic liver toxicity in vivo. In this paper, a state-of-the-art overview of mechanisms and in vitro models of drug-induced cholestatic liver injury is provided.

Stem-cell based organ-on-a-chip models for diabetes research

Diabetes mellitus (DM) ranks among the severest global health concerns of the 21st century. It encompasses a group of chronic disorders characterized by a dysregulated glucose metabolism, which arises as a consequence of progressive autoimmune destruction of pancreatic beta-cells (type 1 DM), or as a result of beta-cell dysfunction combined with systemic insulin resistance (type 2 DM). Human cohort studies have provided evidence of genetic and environmental contributions to DM; yet, these studies are mostly restricted to investigating statistical correlations between DM and certain risk factors. Mechanistic studies, on the other hand, aimed at re-creating the clinical picture of human DM in animal models. A translation to human biology is, however, often inadequate owing to significant differences between animal and human physiology, including the species-specific glucose regulation. Thus, there is an urgent need for the development of advanced human in vitro models with the potential to identify novel treatment options for DM. This review provides an overview of the technological advances in research on DM-relevant stem cells and their integration into microphysiological environments as provided by the organ-on-a-chip technology.

Ex Vivo Model in Cholestasis Research

To mimic (human) cholestasis in vitro requires multiple triggers to establish a diseased phenotype. However, this is currently not simulated by existing in vitro models. Therefore, there is a high need for multicellular systems similar to the human physiology. In such an in vitro model, cell-cell interactions and intact bile canaliculi with functional bile flow should be present and preserved during long-term culture. Precision-cut liver slices represent an ex vivo tissue culture technique that replicates most of the multicellular characteristics of a whole liver in vivo. This chapter describes the preparation and culturing of (human) precision-cut liver slices. Furthermore, a protocol to use the precision-cut liver slices technique to predict drug-induced cholestatic liver injury is described.

Precision-cut human liver slice cultures as an immunological platform

The liver is the central metabolic organ in the human body, and also plays an essential role in innate and adaptive immunity. While mouse models offer significant insights into immune-inflammatory liver disease, human immunology differs in important respects. It is not easy to address those differences experimentally. Therefore, to improve the understanding of human liver immunobiology and pathology, we have established precision-cut human liver slices to study innate immunity in human tissue. Human liver slices collected from resected livers could be maintained in ex vivo culture over a two-week period. Although an acute inflammatory response accompanied by signs of tissue repair was observed in liver tissue following slicing, the expression of many immune genes stabilized after day 4 and remained stable until day 15. Remarkably, histological evidence of pre-existing liver diseases was preserved in the slices for up to 7 days. Following 7 days of culture, exposure of liver slices to the toll-like receptor (TLR) ligands, TLR3 ligand Poly-I:C and TLR4 ligand LPS, resulted in a robust activation of acute inflammation and cytokine genes. Moreover, Poly-I:C treatment induced a marked antiviral response including increases of interferons IFNB, IL-28B and a group of interferon-stimulated genes. Therefore, precision-cut liver slices emerge as a valuable tool to study human innate immunity.

Expression of Organic Anion Transporter 1 or 3 in Human Kidney Proximal Tubule Cells Reduces Cisplatin Sensitivity

Cisplatin is a cytostatic drug used for treatment of solid organ tumors. The main adverse effect is organic cation transporter 2 (OCT2)-mediated nephrotoxicity, observed in 30% of patients. The contribution of other renal drug transporters is elusive. Here, cisplatin-induced toxicity was evaluated in human-derived conditionally immortalized proximal tubule epithelial cells (ciPTEC) expressing renal drug transporters, including OCT2 and organic anion transporters 1 (OAT1) or 3 (OAT3). Parent ciPTEC demonstrated OCT2-dependent cisplatin toxicity (TC₅₀ 34 ± 1 μM after 24-hour exposure), as determined by cell viability. Overexpression of OAT1 and OAT3 resulted in reduced sensitivity to cisplatin (TC₅₀ 45 ± 6 and 64 ± 11 μM after 24-hour exposure, respectively). This effect was independent of OAT-mediated transport, as the OAT substrates probenecid and diclofenac did not influence cytotoxicity. Decreased cisplatin sensitivity in OAT-expressing cells was associated directly with a trend toward reduced intracellular cisplatin accumulation, explained by reduced OCT2 gene expression and activity. This was evaluated by V_max of the OCT2-model substrate ASP⁺ (23.5 ± 0.1, 13.1 ± 0.3, and 21.6 ± 0.6 minutes^-1 in ciPTEC-parent, ciPTEC-OAT1, and ciPTEC-OAT3, respectively). Although gene expression of cisplatin efflux transporter multidrug and toxin extrusion 1 (MATE1) was 16.2 ± 0.3-fold upregulated in ciPTEC-OAT1 and 6.1 ± 0.7-fold in ciPTEC-OAT3, toxicity was unaffected by the MATE substrate pyrimethamine, suggesting that MATE1 does not play a role in the current experimental set-up. In conclusion, OAT expression results in reduced cisplatin sensitivity in renal proximal tubule cells, explained by reduced OCT2-mediated uptake capacity. In vitro drug-induced toxicity studies should consider models that express both OCT and OAT drug transporters.

siRNA-Mediated RNA Interference in Precision-Cut Tissue Slices Prepared from Mouse Lung and Kidney

Small interfering RNA (siRNA)-mediated RNAi interference (RNAi) is a powerful post-transcriptional gene silencing mechanism which can be used to study the function of genes in vitro (cell cultures) and in vivo (animal models). However, there is a translational gap between these models. Hence, there is a need for novel experimental models that combine the advantages of in vitro and in vivo models (e.g., simplicity, flexibility, throughput, and representability) to study the effects of siRNA. This need may be addressed by precision-cut tissue slices (PCTS), which represent an ex vivo model that mimics the structural and functional characteristics of a whole organ. The goal of this study was to investigate whether self-deliverable siRNA (Accell siRNA) can be used in precision-cut lung slices (PCLuS) and precision-cut kidney slices (PCKS) to achieve RNAi ex vivo. PCLuS and PCKS were prepared from mouse tissue, and they were subsequently incubated up to 48 h with no siRNA (untransfected), non-targeting Accell siRNA, or Gapdh-targeting Accell siRNA. Significant Gapdh mRNA silencing was achieved (PCLuS ~ 55%; PCKS ~ 40%) without compromising the viability and morphology of slices. Fluorescence microscopy confirmed that Accell siRNA diffused into PCLuS and PCKS. Spontaneous inflammation upon incubation was observed in PCLuS and PCKS as shown by a higher mRNA expression of pro-inflammatory cytokines Il1b, Il6, and Tnfa, although Accell siRNA appeared to diminish this response in PCLuS after 24 h. In conclusion, this ex vivo transfection model can be used to evaluate the effects of siRNA in relevant biological environments.