Large-Scale Production of LGR5-Positive Bipotential Human Liver Stem Cells.

BACKGROUND AND AIMS: The gap between patients on transplant waiting lists and available donor organs is steadily increasing. Human organoids derived from leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5)-positive adult stem cells represent an exciting new cell source for liver regeneration; however, culturing large numbers of organoids with current protocols is tedious and the level of hepatic differentiation is limited. APPROACH AND RESULTS: Here, we established a method for the expansion of large quantities of human liver organoids in spinner flasks. Due to improved oxygenation in the spinner flasks, organoids rapidly proliferated and reached an average 40-fold cell expansion after 2 weeks, compared with 6-fold expansion in static cultures. The organoids repopulated decellularized liver discs and formed liver-like tissue. After differentiation in spinner flasks, mature hepatocyte markers were highly up-regulated compared with static organoid cultures, and cytochrome p450 activity reached levels equivalent to hepatocytes. CONCLUSIONS: We established a highly efficient method for culturing large numbers of LGR5-positive stem cells in the form of organoids, which paves the way for the application of organoids for tissue engineering and liver transplantation.

The role of extracellular matrix on liver stem cell fate: A dynamic relationship in health and disease.

The liver stem cell niche is a specialized and dynamic microenvironment with biomechanical and biochemical characteristics that regulate stem cell behavior. This is feasible due to the coordination of a complex network of secreted factors, small molecules, neural, blood inputs and extracellular matrix (ECM) components involved in the regulation of stem cell fate (self-renewal, survival, and differentiation into more mature phenotypes like hepatocytes and cholangiocytes). In this review, we describe and summarize all the major components that play essential roles in the liver stem cell niche, in particular, growth factor signaling and the biomechanical properties of the ECM.

Recellularized Native Kidney Scaffolds as a Novel Tool in Nephrotoxicity Screening.

Drug-induced kidney injury in medicinal compound development accounts for over 20% of clinical trial failures and involves damage to different nephron segments, mostly the proximal tubule. Yet, currently applied cell models fail to reliably predict nephrotoxicity; neither are such models easy to establish. Here, we developed a novel three-dimensional (3D) nephrotoxicity platform on the basis of decellularized rat kidney scaffolds (DS) recellularized with conditionally immortalized human renal proximal tubule epithelial cells overexpressing the organic anion transporter 1 (ciPTEC-OAT1). A 5-day SDS-based decellularization protocol was used to generate DS, of which 100-µm slices were cut and used for cell seeding. After 8 days of culturing, recellularized scaffolds (RS) demonstrated 3D-tubule formation along with tubular epithelial characteristics, including drug transporter function. Exposure of RS to cisplatin (CDDP), tenofovir (TFV), or cyclosporin A (CsA) as prototypical nephrotoxic drugs revealed concentration-dependent reduction in cell viability, as assessed by PrestoBlue and Live/Dead staining assays. This was most probably attributable to specific uptake of CDDP by the organic cation transporter 2 (OCT2), TFV through organic anion transporter 1 (OAT1), and CsA competing for P-glycoprotein-mediated efflux. Compared with 2D cultures, RS showed an increased sensitivity to cisplatin and tenofovir toxicity after 24-hour exposure (9 and 2.2 fold, respectively). In conclusion, we developed a physiologically relevant 3D nephrotoxicity screening platform that could be a novel tool in drug development.

Naturally-Derived Biomaterials for Tissue Engineering Applications.

Naturally-derived biomaterials have been used for decades in multiple regenerative medicine applications. From the simplest cell microcarriers made of collagen or alginate, to highly complex decellularized whole-organ scaffolds, these biomaterials represent a class of substances that is usually first in choice at the time of electing a functional and useful biomaterial. Hence, in this chapter we describe the several naturally-derived biomaterials used in tissue engineering applications and their classification, based on composition. We will also describe some of the present uses of the generated tissues like drug discovery, developmental biology, bioprinting and transplantation.

Cetuximab Prevents Methotrexate-Induced Cytotoxicity in Vitro through Epidermal Growth Factor Dependent Regulation of Renal Drug Transporters.

The combination of methotrexate with epidermal growth factor receptor (EGFR) recombinant antibody, cetuximab, is currently being investigated in treatment of head and neck carcinoma. As methotrexate is cleared by renal excretion, we studied the effect of cetuximab on renal methotrexate handling. We used human conditionally immortalized proximal tubule epithelial cells overexpressing either organic anion transporter 1 or 3 (ciPTEC-OAT1/ciPTEC-OAT3) to examine OAT1 and OAT3, and the efflux pumps breast cancer resistance protein (BCRP), multidrug resistance protein 4 (MRP4), and P-glycoprotein (P-gp) in methotrexate handling upon EGF or cetuximab treatment. Protein kinase microarrays and knowledge-based pathway analysis were used to predict EGFR-mediated transporter regulation. Cytotoxic effects of methotrexate were evaluated using the dimethylthiazol bromide (MTT) viability assay. Methotrexate inhibited OAT-mediated fluorescein uptake and decreased efflux of Hoechst33342 and glutathione-methylfluorescein (GS-MF), which suggested involvement of OAT1/3, BCRP, and MRP4 in transepithelial transport, respectively. Cetuximab reversed the EGF-increased expression of OAT1 and BCRP as well as their membrane expressions and transport activities, while MRP4 and P-gp were increased. Pathway analysis predicted cetuximab-induced modulation of PKC and PI3K pathways downstream EGFR/ERBB2/PLCg. Pharmacological inhibition of ERK decreased expression of OAT1 and BCRP, while P-gp and MRP4 were increased. AKT inhibition reduced all transporters. Exposure to methotrexate for 24 h led to a decreased viability, an effect that was reversed by cetuximab. In conclusion, cetuximab downregulates OAT1 and BCRP while upregulating P-gp and MRP4 through an EGFR-mediated regulation of PI3K-AKT and MAPKK-ERK pathways. Consequently, cetuximab attenuates methotrexate-induced cytotoxicity, which opens possibilities for further research into nephroprotective comedication therapies.

A simple method for the isolation and detailed characterization of primary human proximal tubule cells for renal replacement therapy.

The main physiological functions of renal proximal tubule cells in vivo are reabsorption of essential nutrients from the glomerular filtrate and secretion of waste products and xenobiotics into urine. Currently, there are several established cell lines of human origin available as in vitro models of proximal tubule. However, these cells appeared to be limited in their biological relevance, because essential characteristics of the original tissue are lost once the cells are cultured. As a consequence of these limitations, primary human proximal tubule cells constitute a suitable and a biologically more relevant in vitro model to study this specific segment of the nephron and therefore, these cells can play an important role in renal regenerative medicine applications. Here, we describe a protocol to isolate proximal tubule cells from human nephrectomies. We explain the steps performed for an in-depth characterization of the cells, including the study of markers from others segments of the nephron, with the goal to determine the purity of the culture and the stability of proteins, enzymes, and transporters along time. The human proximal tubule cells isolated and used throughout this study showed many proximal tubule characteristics, including monolayer organization, cell polarization with the expression of tight junctions and primary cilia, expression of proximal tubule-specific proteins, such as megalin and sodium/glucose cotransporter 2, among others. The cells also expressed enzymatic activity for dipeptidyl peptidase IV, as well as for gamma glutamyl transferase 1, and expressed transporter activity for organic anion transporter 1, P-glycoprotein, multidrug resistance proteins, and breast cancer resistance protein. In conclusion, characterization of our cells confirmed presence of putative proximal tubule markers and the functional expression of multiple endogenous organic ion transporters mimicking renal reabsorption and excretion. These findings can constitute a valuable tool in the development of bioartificial kidney devices.

Bioengineering Organs for Blood Detoxification.

For patients with severe kidney or liver failure the best solution is currently organ transplantation. However, not all patients are eligible for transplantation and due to limited organ availability, most patients are currently treated with therapies using artificial kidney and artificial liver devices. These therapies, despite their relative success in preserving the patients' life, have important limitations since they can only replace part of the natural kidney or liver functions. As blood detoxification (and other functions) in these highly perfused organs is achieved by specialized cells, it seems relevant to review the approaches leading to bioengineered organs fulfilling most of the native organ functions. There, the culture of cells of specific phenotypes on adapted scaffolds that can be perfused takes place. In this review paper, first the functions of kidney and liver organs are briefly described. Then artificial kidney/liver devices, bioartificial kidney devices, and bioartificial liver devices are focused on, as well as biohybrid constructs obtained by decellularization and recellularization of animal organs. For all organs, a thorough overview of the literature is given and the perspectives for their application in the clinic are discussed.

In vitro systems to study nephropharmacology: 2D versus 3D models.

The conventional 2-dimensional (2D) cell culture is an invaluable tool in, amongst others, cell biology and experimental pharmacology. However, cells cultured in 2D, on the top of stiff plastic plates lose their phenotypical characteristics and fail in recreating the physiological environment found in vivo. This is a fundamental requirement when the goal of the study is to get a rigorous predictive response of human drug action and safety. Recent approaches in the field of renal cell biology are focused on the generation of 3D cell culture models due to the more bona fide features that they exhibit and the fact that they are more closely related to the observed physiological conditions, and better predict in vivo drug handling. In this review, we describe the currently available 3D in vitro models of the kidney, and some future directions for studying renal drug handling, disease modeling and kidney regeneration.