Characterization of primary rat proximal tubular cells by gene expression analysis

Safety evaluation of conditionally immortalized cells for renal replacement therapy

End-stage kidney disease represents irreversible kidney failure. Dialysis and transplantation, two main treatment options currently available, present various drawbacks and complications. Innovative cell-based therapies, such as a bioartificial kidney, have not reached the clinic yet, mostly due to safety and/or functional issues. Here, we assessed the safety of conditionally immortalized proximal tubule epithelial cells (ciPTECs) for bioartificial kidney application, by using in vitro assays and athymic nude rats. We demonstrate that these cells do not possess key properties of oncogenically transformed cells, including anchorage-independent growth, lack of contact inhibition and apoptosis-resistance. In late-passage cells we did observe complex chromosomal abnormalities favoring near-tetraploidy, indicating chromosomal instability. However, time-lapse imaging of ciPTEC-OAT1, confined to a 3D extracellular matrix (ECM)-based environment, revealed that the cells were largely non-invasive. Furthermore, we determined the viral integration sites of SV40 Large T antigen (SV40T), human telomerase (hTERT) and OAT1 (SLC22A6), the transgenes used for immortalization and cell function enhancement. All integrations sites were found to be located in the intronic regions of endogenous genes. Among these genes, early endosome antigen 1 (EEA1) involved in endocytosis, and BCL2 Like 1 (BCL2L1) known for its role in regulating apoptosis, were identified. Nevertheless, both gene products appeared to be functionally intact. Finally, after subcutaneous injection in athymic nude rats we show that ciPTEC-OAT1 lack tumorigenic and oncogenic effects in vivo, confirming the in vitro findings. Taken together, this study lays an important foundation towards bioartificial kidney (BAK) development by confirming the safety of the cell line intended for incorporation.

Cannabinoid-1 receptor regulates mitochondrial dynamics and function in renal proximal tubular cells

AIMS

To evaluate the specific role of the endocannabinoid/cannabinoid type-1 (CB₁ R) system in modulating mitochondrial dynamics in the metabolically active renal proximal tubular cells (RPTCs).

MATERIALS AND METHODS

We utilized mitochondrially-targeted GFP in live cells (wild-type and null for the CB₁ R) and electron microscopy in kidney sections of RPTC-CB₁ R^-/- mice and their littermate controls. In both in vitro and in vivo conditions, we assessed the ability of CB₁ R agonism or fatty acid flux to modulate mitochondrial architecture and function.

RESULTS

Direct stimulation of CB₁ R resulted in mitochondrial fragmentation in RPTCs. This process was mediated, at least in part, by modulating the phosphorylation levels of the canonical fission protein dynamin-related protein 1 on both S637 and S616 residues. CB₁ R-induced mitochondrial fission was associated with mitochondrial dysfunction, as documented by reduced oxygen consumption and ATP production, increased reactive oxygen species and cellular lactate levels, as well as a decline in mitochondrial biogenesis. Likewise, we documented that exposure of RPTCs to a fatty acid flux induced CB₁ R-dependent mitochondrial fission, lipotoxicity and cellular dysfunction.

CONCLUSIONS

CB₁ R plays a key role in inducing mitochondrial fragmentation in RPTCs, leading to a decline in the organelle's function and contributing to the renal tubular injury associated with lipotoxicity and other metabolic diseases.

High-throughput prediction of nephrotoxicity in humans

The Lush Science Prize 2016 was awarded to Daniele Zink and Lit-Hsin Loo for the interdisciplinary and collaborative work between their research groups in developing alternative methods for the prediction of nephrotoxicity in humans. The collaboration has led to the establishment of a series of pioneering alternative methods for nephrotoxicity prediction, which includes: predictive gene expression markers based on pro-inflammatory responses; predictive in vitro cellular models based on pluripotent stem cell-derived proximal tubular-like cells; and predictive cellular phenotypic markers based on chromatin and cytoskeletal changes. A high-throughput method was established for chemical testing, which is currently being used to predict the potential human nephrotoxicity of ToxCast compounds in collaboration with the US Environmental Protection Agency. Similar high-throughput imaging-based methodologies are currently being developed and adapted by the Zink and Loo groups, to include other human organs and cell types. The ultimate goal is to develop a portfolio of methods accepted for the accurate prediction of human organ-specific toxicity and the consequent replacement of animal experiments.

Stem cell-derived kidney cells and organoids: Recent breakthroughs and emerging applications

The global rise in the numbers of kidney patients and the shortage in transplantable organs have led to an increasing interest in kidney-specific regenerative therapies, renal disease modelling and bioartificial kidneys. Sources for large quantities of high-quality renal cells and tissues would be required, also for applications in in vitro platforms for compound safety and efficacy screening. Stem cell-based approaches for the generation of renal-like cells and tissues would be most attractive, but such methods were not available until recently. This situation has drastically changed since 2013, and various protocols for the generation of renal-like cells and precursors from pluripotent stem cells (PSC) have been established. The most recent breakthroughs were related to the establishment of various protocols for the generation of PSC-derived kidney organoids. In combination with recent advances in genome editing, bioprinting and the establishment of predictive renal screening platforms this results in exciting new possibilities. This review will give a comprehensive overview over current PSC-based protocols for the generation of renal-like cells, precursors and organoids, and their current and potential applications in regenerative medicine, compound screening, disease modelling and bioartificial organs.

Polydatin Protecting Kidneys against Hemorrhagic Shock-Induced Mitochondrial Dysfunction via SIRT1 Activation and p53 Deacetylation

Objectives. To ascertain if mitochondrial dysfunction (MD) of kidney cells is present in severe hemorrhagic shock and to investigate whether polydatin (PD) can attenuate MD and its protective mechanisms. Research Design and Methods. Renal tubular epithelial cells (RTECs) from rat kidneys experiencing HS and a cell line (HK-2) under hypoxia/reoxygenation (H/R) treatment were used. Morphology and function of mitochondria in isolated RTECs or cultured HK-2 cells were evaluated, accompanied by mitochondrial apoptosis pathway-related proteins. Result. Severe MD was found in rat kidneys, especially in RTECs, as evidenced by swollen mitochondria and poorly defined cristae, decreased mitochondrial membrane potential (ΔΨm), and reduced ATP content. PD treatment attenuated MD partially and inhibited expression of proapoptotic proteins. PD treatment increased SIRT1 activity and decreased acetylated-p53 levels. Beneficial effect of PD was abolished partially when the SIRT1 inhibitor Ex527 was added. Similar phenomena were shown in the H/R cell model; when pifithrin-α (p53 inhibitor) was added to the PD/Ex527 group, considerable therapeutic effects were regained compared with the PD group apart from increased SIRT1 activity. Conclusions. MD is present in severe HS, and PD can attenuate MD of RTECs via the SIRT1-p53 pathway. PD might be a promising therapeutic drug for acute renal injury.

Polydatin Inhibits Mitochondrial Dysfunction in the Renal Tubular Epithelial Cells of a Rat Model of Sepsis-Induced Acute Kidney Injury

BACKGROUND

Mitochondrial injury is a major cause of sepsis-induced organ failure. Polydatin (PD), a natural polyphenol, demonstrates protective mitochondrial effects in neurons and arteriolar smooth muscle cells during severe shock. In this study, we investigated the effects of PD on renal tubular epithelial cell (RTEC) mitochondria in a rat model of sepsis-induced acute kidney injury.

METHODS

Rats underwent cecal ligation and puncture (CLP) to mimic sepsis-induced acute kidney injury. Rats were randomly divided into sham, CLP + normal saline, CLP + vehicle, and CLP + PD groups. Normal saline, vehicle, and 30 mg/kg PD were administered at 6, 12, and 18 hours after CLP or sham surgery via the tail vein. Mitochondrial morphology, metabolism, and function in RTECs were then assessed. Serum cytokines, renal function, survival, and histologic changes in the kidney were also evaluated.

RESULTS

CLP increased lipid peroxide content, lysosomal instability, and opening of the mitochondrial permeability transition pore and caused mitochondrial swelling. Moreover, mitochondrial membrane potential (ΔΨm) was decreased and ATP levels reduced after CLP. PD inhibited all the above effects. It also inhibited the inflammatory response, improved renal function, attenuated histologic indicators of kidney damage, and prolonged survival.

CONCLUSIONS

PD protects RTECs against mitochondrial dysfunction and prolongs survival in a rat model of sepsis-induced acute kidney injury. These effects may partially result from reductions in interleukin-6 and oxidative stress.

Prediction of drug-induced nephrotoxicity and injury mechanisms with human induced pluripotent stem cell-derived cells and machine learning methods

The renal proximal tubule is a main target for drug-induced toxicity. The prediction of proximal tubular toxicity during drug development remains difficult. Any in vitro methods based on induced pluripotent stem cell-derived renal cells had not been developed, so far. Here, we developed a rapid 1-step protocol for the differentiation of human induced pluripotent stem cells (hiPSC) into proximal tubular-like cells. These proximal tubular-like cells had a purity of >90% after 8 days of differentiation and could be directly applied for compound screening. The nephrotoxicity prediction performance of the cells was determined by evaluating their responses to 30 compounds. The results were automatically determined using a machine learning algorithm called random forest. In this way, proximal tubular toxicity in humans could be predicted with 99.8% training accuracy and 87.0% test accuracy. Further, we studied the underlying mechanisms of injury and drug-induced cellular pathways in these hiPSC-derived renal cells, and the results were in agreement with human and animal data. Our methods will enable the development of personalized or disease-specific hiPSC-based renal in vitro models for compound screening and nephrotoxicity prediction.

Drug-induced nephrotoxicity: clinical impact and preclinical in vitro models

The kidney is a major target for drug-induced toxicity. Drug-induced nephrotoxicity remains a major problem in the clinical setting, where the use of nephrotoxic drugs is often unavoidable. This leads frequently to acute kidney injury, and current problems are discussed. One strategy to avoid such problems would be the development of drugs with decreased nephrotoxic potential. However, the prediction of nephrotoxicity during preclinical drug development is difficult and nephrotoxicity is typically detected only late. Also, the nephrotoxic potential of newly approved drugs is often underestimated. Regulatory approved or validated in vitro models for the prediction of nephrotoxicity are currently not available. Here, we will review current approaches on the development of such models. This includes a discussion of three-dimensional and microfluidic models and recently developed stem cell based approaches. Most in vitro models have been tested with a limited number of compounds and are of unclear predictivity. However, some studies have tested larger numbers of compounds and the predictivity of the respective in vitro model had been determined. The results showed that high predictivity can be obtained by using primary or stem cell derived human renal cells in combination with appropriate end points.

Isolation and characterization of a primary proximal tubular epithelial cell model from human kidney by CD10/CD13 double labeling

Renal proximal tubular epithelial cells play a central role in renal physiology and are among the cell types most sensitive to ischemia and xenobiotic nephrotoxicity. In order to investigate the molecular and cellular mechanisms underlying the pathophysiology of kidney injuries, a stable and well-characterized primary culture model of proximal tubular cells is required. An existing model of proximal tubular cells is hampered by the cellular heterogeneity of kidney; a method based on cell sorting for specific markers must therefore be developed. In this study, we present a primary culture model based on the mechanical and enzymatic dissociation of healthy tissue obtained from nephrectomy specimens. Renal epithelial cells were sorted using co-labeling for CD10 and CD13, two renal proximal tubular epithelial markers, by flow cytometry. Their purity, phenotypic stability and functional properties were evaluated over several passages. Our results demonstrate that CD10/CD13 double-positive cells constitute a pure, functional and stable proximal tubular epithelial cell population that displays proximal tubule markers and epithelial characteristics over the long term, whereas cells positive for either CD10 or CD13 alone appear to be heterogeneous. In conclusion, this study describes a method for establishing a robust renal proximal tubular epithelial cell model suitable for further experimentation.

Bioengineered 3D human kidney tissue, a platform for the determination of nephrotoxicity

The staggering cost of bringing a drug to market coupled with the extremely high failure rate of prospective compounds in early phase clinical trials due to unexpected human toxicity makes it imperative that more relevant human models be developed to better predict drug toxicity. Drug–induced nephrotoxicity remains especially difficult to predict in both pre-clinical and clinical settings and is often undetected until patient hospitalization. Current pre-clinical methods of determining renal toxicity include 2D cell cultures and animal models, both of which are incapable of fully recapitulating the in vivo human response to drugs, contributing to the high failure rate upon clinical trials. We have bioengineered a 3D kidney tissue model using immortalized human renal cortical epithelial cells with kidney functions similar to that found in vivo. These 3D tissues were compared to 2D cells in terms of both acute (3 days) and chronic (2 weeks) toxicity induced by Cisplatin, Gentamicin, and Doxorubicin using both traditional LDH secretion and the pre-clinical biomarkers Kim-1 and NGAL as assessments of toxicity. The 3D tissues were more sensitive to drug-induced toxicity and, unlike the 2D cells, were capable of being used to monitor chronic toxicity due to repeat dosing. The inclusion of this tissue model in drug testing prior to the initiation of phase I clinical trials would allow for better prediction of the nephrotoxic effects of new drugs.

SnoN as a key regulator of the high glucose-induced epithelial-mesenchymal transition in cells of the proximal tubule

BACKGROUND/AIMS

Ski-related protein N (SnoN) suppression is essential to transforming growth factor-β1 induction and the epithelial-mesenchymal transition (EMT) in several cancer cells. The role of SnoN in diabetic nephropathy is unknown. We aimed to determine the role of SnoN in the EMT of proximal tubule cells (PTCs) maintained under high glucose conditions.

METHODS

Immunohistochemistry, immunocytochemistry, Western blotting, small interfering RNA gene silencing, viral transduction and RT-PCR were used to assess changes in SnoN, E-cadherin, cytokeratin-18, α-smooth muscle actin and fibronectin expression using an in vivo streptozotocin-induced rat diabetic nephropathy model, and PTCs exposed to high glucose (25 mmol/l).

RESULTS

High glucose induced EMT in vitro and in vivo. Exposure of PTCs to a high concentration of glucose suppressed SnoN expression in a time-dependent manner compared with normal glucose and high osmolarity-treated groups. SnoN gene silencing under high glucose conditions appears to enhance the transition of PTC phenotype. Conversely, ectopic expression of exogenous SnoN after transfection conferred tubular epithelial cell resistance to high glucose-induced EMT.

CONCLUSION

SnoN plays a negative role in high glucose-induced EMT in PTCs. The effect of SnoN downregulation in vivo and in vitro suggests that SnoN may be a potential therapeutic target.

Alternative (non-animal) methods for cosmetics testing: current status and future prospects-2010

The 7th amendment to the EU Cosmetics Directive prohibits to put animal-tested cosmetics on the market in Europe after 2013. In that context, the European Commission invited stakeholder bodies (industry, non-governmental organisations, EU Member States, and the Commission's Scientific Committee on Consumer Safety) to identify scientific experts in five toxicological areas, i.e. toxicokinetics, repeated dose toxicity, carcinogenicity, skin sensitisation, and reproductive toxicity for which the Directive foresees that the 2013 deadline could be further extended in case alternative and validated methods would not be available in time. The selected experts were asked to analyse the status and prospects of alternative methods and to provide a scientifically sound estimate of the time necessary to achieve full replacement of animal testing. In summary, the experts confirmed that it will take at least another 7-9 years for the replacement of the current in vivo animal tests used for the safety assessment of cosmetic ingredients for skin sensitisation. However, the experts were also of the opinion that alternative methods may be able to give hazard information, i.e. to differentiate between sensitisers and non-sensitisers, ahead of 2017. This would, however, not provide the complete picture of what is a safe exposure because the relative potency of a sensitiser would not be known. For toxicokinetics, the timeframe was 5-7 years to develop the models still lacking to predict lung absorption and renal/biliary excretion, and even longer to integrate the methods to fully replace the animal toxicokinetic models. For the systemic toxicological endpoints of repeated dose toxicity, carcinogenicity and reproductive toxicity, the time horizon for full replacement could not be estimated.

Inhibition of cadmium-induced apoptosis by glutathione S-transferase P1 via mitogen-activated protein kinases and mitochondrial pathways

Cadmium is a well-known toxic metal for the kidney. Glutathione S-transferase P1 (GSTP1) plays an important role in the detoxification and xenobiotics metabolism. Here, we investigated whether GSTP1 affected Cd(2+)-induced apoptotic cell death in human embryonic kidney cell line (HEK) 293 cells. We showed that in HEK293 cells, silencing of GSTP1 expression through RNA interference reinforced the loss in cell viability induced by Cd(2+). Overexpression of GSTP1 inhibited loss of mitochondrial membrane potential, prevented cytochrome c release from mitochondria and caspase-3 activation, inhibited mitogen-activated protein kinases (MAPKs) including ERK, JNK and p38, and suppressed apoptosis induced by Cd(2+). The oligonucleosomal DNA fragmentation assay also demonstrated that overexpression of GSTP1 by adenovirus infection prevented Cd(2+)-induced apoptosis in primary renal tubule cells. Our data suggest that GSTP1 was an endogenous inhibitor of Cd(2+)-induced apoptosis.

Achievements and challenges in bioartificial kidney development

Bioartificial kidneys (BAKs) combine a conventional hemofilter in series with a bioreactor unit containing renal epithelial cells. The epithelial cells derived from the renal tubule should provide transport, metabolic, endocrinologic and immunomodulatory functions. Currently, primary human renal proximal tubule cells are most relevant for clinical applications. However, the use of human primary cells is associated with many obstacles, and the development of alternatives and an unlimited cell source is one of the most urgent challenges. BAKs have been applied in Phase I/II and Phase II clinical trials for the treatment of critically ill patients with acute renal failure. Significant effects on cytokine concentrations and long-term survival were observed. A subsequent Phase IIb clinical trial was discontinued after an interim analysis, and these results showed that further intense research on BAK-based therapies for acute renal failure was required. Development of BAK-based therapies for the treatment of patients suffering from end-stage renal disease is even more challenging, and related problems and research approaches are discussed herein, along with the development of mobile, portable, wearable and implantable devices.

Impact of Cyclin B2 and Cell division cycle 2 on tubular hyperplasia in progressive chronic renal failure rats

To clarify the specific molecular events of progressive tubular damage in chronic renal failure (CRF), we conducted microarray analyses using isolated proximal tubules from subtotally nephrectomized (Nx) rats as a model of CRF. Our results clearly demonstrated time-dependent changes in gene expression profiles localized to proximal tubules. The expression of mitosis-specific genes Cyclin B2 and Cell division cycle 2 (Cdc2) was significantly and selectively increased in the proximal tubules during the compensated period but decreased to basal level in the end-stage period. Administration of everolimus, a potent inhibitor of mammalian target of rapamycin, markedly reduced compensatory hypertrophy and hyperplasia of epithelial cells, which was accompanied by complete abolishment of the expression of Cyclin B2 and Cdc2 enhancement; renal function was then severely decreased. Treatment with the Cdc2 inhibitor 2-cyanoethyl alsterpaullone clearly decreased epithelial cell hyperplasia, based on staining of phosphorylated histone H3 and Ki-67, while hypertrophy was not inhibited. In conclusion, we have demonstrated roles of Cyclin B2 and Cdc2 in the epithelial hyperplasia in response to Nx. These results advance the knowledge of the contribution of cell cycle regulators, especially M phase, in pathophysiology of tubular restoration and/or degeneration, and these two molecules are suggested to be a marker for the proliferation of proximal tubular cells in CRF.

Novel conditionally immortalized human proximal tubule cell line expressing functional influx and efflux transporters

Reabsorption of filtered solutes from the glomerular filtrate and excretion of waste products and xenobiotics are the main functions of the renal proximal tubular (PT) epithelium. A human PT cell line expressing a range of functional transporters would help to augment current knowledge in renal physiology and pharmacology. We have established and characterized a conditionally immortalized PT epithelial cell line (ciPTEC) obtained by transfecting and subcloning cells exfoliated in the urine of a healthy volunteer. The PT origin of this line has been confirmed morphologically and by the expression of aminopeptidase N, zona occludens 1, aquaporin 1, dipeptidyl peptidase IV and multidrug resistance protein 4 together with alkaline phosphatase activity. ciPTEC assembles in a tight monolayer with limited diffusion of inulin-fluorescein-isothiocyanate. Concentration and time-dependent reabsorption of albumin via endocytosis has been demonstrated, together with sodium-dependent phosphate uptake. The expression and activity of apical efflux transporter p-glycoprotein and of baso-lateral influx transporter organic cation transporter 2 have been shown in ciPTEC. This established human ciPTEC expressing multiple endogenous organic ion transporters mimicking renal reabsorption and excretion represents a powerful tool for future in vitro transport studies in pharmacology and physiology.

Evaluation of putative biomarkers of nephrotoxicity after exposure to ochratoxin a in vivo and in vitro

The kidney is one of the main targets of xenobiotic-induced toxicity, but early detection of renal damage is difficult. Recently, several novel biomarkers of nephrotoxicity have been identified by transcription profiling, including kidney injury molecule-1 (Kim-1), lipocalin-2, tissue inhibitor of metalloproteinases-1 (Timp-1), clusterin, osteopontin (OPN), and vimentin, and suggested as sensitive endpoints for acute kidney injury in vivo. However, it is not known if these cellular marker molecules may also be useful to predict chronic nephrotoxicity or to detect nephrotoxic effects in vitro. In this study, a panel of new biomarkers of renal toxicity was assessed via quantitative real-time PCR, immunohistochemistry, and immunoblotting in rats treated with the nephrotoxin ochratoxin A (OTA) for up to 90 days and in rat proximal tubule cells (NRK-52E) treated with OTA in vitro. Repeated administration of OTA to male F344/N rats for 14, 28, or 90 days resulted in a dose- and time-dependent increase in the expression of Kim-1, Timp-1, lipocalin-2, OPN, clusterin, and vimentin. Changes in gene expression were found to correlate with the progressive histopathological alterations and preceded effects on traditional clinical parameters indicative of impaired kidney function. Induction of Kim-1 messenger RNA expression was the earliest and most prominent response observed, supporting the use of this marker as sensitive indicator of chronic kidney injury. In contrast, no significant increase in the expression of putative marker genes and proteins were evident in NRK-52E cells after exposure to OTA for up to 48 h, suggesting that they may not be suitable endpoints for sensitive detection of nephrotoxic effects in vitro.