Analysis of transcriptomic and proteomic profiles demonstrates improved Madin-Darby canine kidney cell function in a renal microfluidic biochip

Regulation of cell fate by cell imprinting approach in vitro

Cell culture-based technologies are widely utilized in various domains such as drug evaluation, toxicity assessment, vaccine and biopharmaceutical development, reproductive technology, and regenerative medicine. It has been demonstrated that pre-adsorption of extracellular matrix (ECM) proteins including collagen, laminin and fibronectin provide more degrees of support for cell adhesion. The purpose of cell imprinting is to imitate the natural topography of cell membranes by gels or polymers to create a reliable environment for the regulation of cell function. The results of recent studies show that cell imprinting is a tool to guide the behavior of cultured cells by controlling their adhesive interactions with surfaces. Therefore, in this review we aim to compare different cell cultures with the imprinting method and discuss different cell imprinting applications in regenerative medicine, personalized medicine, disease modeling, and cell therapy.

A quantitative meta-analysis comparing cell models in perfused organ on a chip with static cell cultures

As many consider organ on a chip for better in vitro models, it is timely to extract quantitative data from the literature to compare responses of cells under flow in chips to corresponding static incubations. Of 2828 screened articles, 464 articles described flow for cell culture and 146 contained correct controls and quantified data. Analysis of 1718 ratios between biomarkers measured in cells under flow and static cultures showed that the in all cell types, many biomarkers were unregulated by flow and only some specific biomarkers responded strongly to flow. Biomarkers in cells from the blood vessels walls, the intestine, tumours, pancreatic island, and the liver reacted most strongly to flow. Only 26 biomarkers were analysed in at least two different articles for a given cell type. Of these, the CYP3A4 activity in CaCo2 cells and PXR mRNA levels in hepatocytes were induced more than two-fold by flow. Furthermore, the reproducibility between articles was low as 52 of 95 articles did not show the same response to flow for a given biomarker. Flow showed overall very little improvements in 2D cultures but a slight improvement in 3D cultures suggesting that high density cell culture may benefit from flow. In conclusion, the gains of perfusion are relatively modest, larger gains are linked to specific biomarkers in certain cell types.

Dynamic single cell analysis in a proximal-tubule-on-chip reveals heterogeneous epithelial colonization strategies of uropathogenic Escherichia coli under shear stress

The urinary tract is a hydrodynamically challenging microenvironment and uropathogenic Escherichia coli (UPEC) must overcome several physiological challenges in order to adhere and establish a urinary tract infection. Our previous work in vivo revealed a synergy between different UPEC adhesion organelles, which facilitated effective colonization of the renal proximal tubule. To allow high-resolution real-time analysis of this colonization behavior, we established a biomimetic proximal-tubule-on-chip (PToC). The PToC allowed for single-cell resolution analysis of the first stages of bacterial interaction with host epithelial cells, under physiological flow. Time-lapse microscopy and single-cell trajectory analysis in the PToC revealed that while the majority of UPEC moved directly through the system, a minority population initiated heterogeneous adhesion, identified as either rolling or bound. Adhesion was predominantly transient and mediated by P pili at the earliest time-points. These bound bacteria initiated a founder population which rapidly divided, leading to 3D microcolonies. Within the first hours, the microcolonies did not express extracellular curli matrix, but rather were dependent on Type 1 fimbriae as the key element in the microcolony structure. Collectively, our results show the application of Organ-on-chip technology to address bacterial adhesion behaviors, demonstrating a well-orchestrated interplay and redundancy between adhesion organelles that enables UPEC to form microcolonies and persist under physiological shear stress.

Fluid shear stress affects the metabolic and toxicological response of the rainbow trout gill cell line RTgill-W1

The Rainbow trout gill cell-line (RTgill-W1) has been accepted by the Organisation for Economic Co-operation and Development (OECD TG249) as a replacement for fish in acute toxicity tests. In these tests cells are exposed under static conditions. In contrast, in vivo, water moves over fish gills generating fluid shear stress (FSS) that alters cell physiology and response to toxicants. The current study uses a specialised 3D printed chamber designed to house inserts and allows for the flow (0.2 dynes cm²) of water over the cells. This system was used to assess RTgill-W1 cell responses to FSS in the absence and presence of copper (Cu) over 24 h. FSS caused increased gene expression of mechanosensitive channel peizo1 and the Cu-transporter atp7a, elevated reactive oxygen species generation and increased expression of superoxidase dismutase. Cell metabolism was unaffected by Cu (0.163 μM to 2.6 μM Cu) under static conditions but significantly reduced by FSS + Cu above 1.3 μM. Differential expression of metallothionein (mt) a and b was observed with increased expression of mta under static conditions and mtb under FSS on exposure to Cu. These findings highlight toxicologically relevant mechanosensory responses by RTgill-W1 to FSS that may influence toxicological responses.

Primary exploration of host-microorganism interaction and enteritis treatment with an embedded membrane microfluidic chip of the human intestinal-vascular microsystem

Intestinal flora plays a crucial role in the host's intestinal health. Imbalances in the intestinal flora, when accompanied by inflammation, affect the host's intestinal barrier function. Understanding it requires studying how living cells and tissues work in the context of living organs, but it is difficult to form the three-dimensional microstructure intestinal-vascular system by monolayer cell or co-culture cell models, and animal models are costly and slow. The use of microfluidic-based organ chips is a fast, simple, and high-throughput method that not only solves the affinity problem of animal models but the lack of microstructure problem of monolayer cells. In this study, we designed an embedded membrane chip to generate an in vitro gut-on-a-chip model. Human umbilical vein endothelial cells and Caco-2 were cultured in the upper and lower layers of the culture chambers in the microfluidic chip, respectively. The human peripheral blood mononuclear cells were infused into the capillary side at a constant rate using an external pump to simulate the in vitro immune system and the shear stress of blood in vivo. The model exhibited intestine morphology and function after only 5 days of culture, which is significantly less than the 21 days required for static culture in the Transwell^® chamber. Furthermore, it was observed that drug-resistant bacteria triggered barrier function impairment and inflammation, resulting in enteritis, whereas probiotics (Lactobacillus rhamnosus GG) improved only partially. The use of Amikacin for enteritis is effective, whereas other antibiotic therapies do not work, which are consistent with clinical test results. This model may be used to explore intestinal ecology, host and intestinal flora interactions, and medication assessment.

Applications of Polymers for Organ-on-Chip Technology in Urology

Organ-on-chips (OOCs) are microfluidic devices used for creating physiological organ biomimetic systems. OOC technology brings numerous advantages in the current landscape of preclinical models, capable of recapitulating the multicellular assemblage, tissue-tissue interaction, and replicating numerous human pathologies. Moreover, in cancer research, OOCs emulate the 3D hierarchical complexity of in vivo tumors and mimic the tumor microenvironment, being a practical cost-efficient solution for tumor-growth investigation and anticancer drug screening. OOCs are compact and easy-to-use microphysiological functional units that recapitulate the native function and the mechanical strain that the cells experience in the human bodies, allowing the development of a wide range of applications such as disease modeling or even the development of diagnostic devices. In this context, the current work aims to review the scientific literature in the field of microfluidic devices designed for urology applications in terms of OOC fabrication (principles of manufacture and materials used), development of kidney-on-chip models for drug-toxicity screening and kidney tumors modeling, bladder-on-chip models for urinary tract infections and bladder cancer modeling and prostate-on-chip models for prostate cancer modeling.

In Vitro–In Silico Modeling of Caffeine and Diclofenac Permeation in Static and Fluidic Systems with a 16HBE Lung Cell Barrier

Static in vitro permeation experiments are commonly used to gain insights into the permeation properties of drug substances but exhibit limitations due to missing physiologic cell stimuli. Thus, fluidic systems integrating stimuli, such as physicochemical fluxes, have been developed. However, as fluidic in vitro studies display higher complexity compared to static systems, analysis of experimental readouts is challenging. Here, the integration of in silico tools holds the potential to evaluate fluidic experiments and to investigate specific simulation scenarios. This study aimed to develop in silico models that describe and predict the permeation and disposition of two model substances in a static and fluidic in vitro system. For this, in vitro permeation studies with a 16HBE cellular barrier under both static and fluidic conditions were performed over 72 h. In silico models were implemented and employed to describe and predict concentration–time profiles of caffeine and diclofenac in various experimental setups. For both substances, in silico modeling identified reduced apparent permeabilities in the fluidic compared to the static cellular setting. The developed in vitro–in silico modeling framework can be expanded further, integrating additional cell tissues in the fluidic system, and can be employed in future studies to model pharmacokinetic and pharmacodynamic drug behavior.

Advanced In Vitro Lung Models for Drug and Toxicity Screening: The Promising Role of Induced Pluripotent Stem Cells

The substantial socioeconomic burden of lung diseases, recently highlighted by the disastrous impact of the coronavirus disease 2019 (COVID-19) pandemic, accentuates the need for interventive treatments capable of decelerating disease progression, limiting organ damage, and contributing to a functional tissue recovery. However, this is hampered by the lack of accurate human lung research models, which currently fail to reproduce the human pulmonary architecture and biochemical environment. Induced pluripotent stem cells (iPSCs) and organ-on-chip (OOC) technologies possess suitable characteristics for the generation of physiologically relevant in vitro lung models, allowing for developmental studies, disease modeling, and toxicological screening. Importantly, these platforms represent potential alternatives for animal testing, according to the 3Rs (replace, reduce, refine) principle, and hold promise for the identification and approval of new chemicals under the European REACH (registration, evaluation, authorization and restriction of chemicals) framework. As such, this review aims to summarize recent progress made in human iPSC- and OOC-based in vitro lung models. A general overview of the present applications of in vitro lung models is presented, followed by a summary of currently used protocols to generate different lung cell types from iPSCs. Lastly, recently developed iPSC-based lung models are discussed.

Usability of Polydimethylsiloxane-Based Microfluidic Devices in Pharmaceutical Research Using Human Hepatocytes

A liver-on-a-chip (liver-chip) is a microfluidic device carrying liver cells such as human hepatocytes. It is used to reproduce a part of liver function. Many microfluidic devices are composed of polydimethylsiloxane (PDMS), which is a type of silicone elastomer. PDMS is easy to process and suitable for cell observation, but its high hydrophobicity carries the risk of drug absorption. In this study, we evaluated drug absorption to the PDMS device and investigated the drug responsiveness of human hepatocytes cultured in the PDMS device (hepatocyte-chips). First, the absorption rates of 12 compounds to the PDMS device were measured. The absorption rates of midazolam, bufuralol, cyclosporine A, and verapamil were 92.9, 71.7, 71.4, and 99.6%, respectively, but the other compounds were poorly absorbed. Importantly, the absorption rate of the compounds was correlated with their octanol/water distribution coefficient (log D) values (R² = 0.76). Next, hepatocyte-chips were used to examine the response to drugs, which are typically used to evaluate hepatic functions. Using the hepatocyte-chips, we could confirm the responsiveness of drugs including cytochrome P450 (CYP) inducers and farnesoid X receptor (FXR) ligands. We believe that our findings will contribute to drug discovery research using PDMS-based liver-chips.

Recurrent Urinary Tract Infection: A Mystery in Search of Better Model Systems

Urinary tract infections (UTIs) are among the most common infectious diseases worldwide but are significantly understudied. Uropathogenic E. coli (UPEC) accounts for a significant proportion of UTI, but a large number of other species can infect the urinary tract, each of which will have unique host-pathogen interactions with the bladder environment. Given the substantial economic burden of UTI and its increasing antibiotic resistance, there is an urgent need to better understand UTI pathophysiology - especially its tendency to relapse and recur. Most models developed to date use murine infection; few human-relevant models exist. Of these, the majority of in vitro UTI models have utilized cells in static culture, but UTI needs to be studied in the context of the unique aspects of the bladder's biophysical environment (e.g., tissue architecture, urine, fluid flow, and stretch). In this review, we summarize the complexities of recurrent UTI, critically assess current infection models and discuss potential improvements. More advanced human cell-based in vitro models have the potential to enable a better understanding of the etiology of UTI disease and to provide a complementary platform alongside animals for drug screening and the search for better treatments.

Potential Applications of Microfluidics to Acute Kidney Injury Associated with Viral Infection

The kidneys are susceptible to adverse effects from many diseases, including several that are not tissue-specific. Acute kidney injury is a common complication of systemic diseases such as diabetes, lupus, and certain infections including the novel coronavirus (SARS-CoV-2). Microfluidic devices are an attractive option for disease modeling, offering the opportunity to utilize human cells, control experimental and environmental conditions, and combine with other on-chip devices. For researchers with expertise in microfluidics, this brief perspective highlights potential applications of such devices to studying SARS-CoV-2-induced kidney injury.

Drug Toxicity Evaluation Based on Organ-on-a-chip Technology: A Review

Organ-on-a-chip academic research is in its blossom. Drug toxicity evaluation is a promising area in which organ-on-a-chip technology can apply. A unique advantage of organ-on-a-chip is the ability to integrate drug metabolism and drug toxic processes in a single device, which facilitates evaluation of toxicity of drug metabolites. Human organ-on-a-chip has been fabricated and used to assess drug toxicity with data correlation with the clinical trial. In this review, we introduced the microfluidic chip models of liver, kidney, heart, nerve, and other organs and multiple organs, highlighting the application of these models in drug toxicity detection. Some biomarkers of toxic injury that have been used in organ chip platforms or have potential for use on organ chip platforms are summarized. Finally, we discussed the goals and future directions for drug toxicity evaluation based on organ-on-a-chip technology.

Emerging In Vitro Systems to Screen and Predict Drug-Induced Kidney Toxicity

Drug attrition related to kidney toxicity remains a challenge in drug discovery and development. In vitro models established over the past 2 decades to supplement in vivo studies have improved the throughput capacity of toxicity evaluation, but usually suffer from low predictive value. To achieve a paradigm shift in the prediction of drug-induced kidney toxicity, two aspects are fundamental: increased physiological relevance of the kidney model, and use of appropriate toxicity end points. Recent studies have suggested that increasing the physiological relevance of kidney models can improve their sensitivity to drug-induced damage. Here, we discuss how advanced culture models, including modified cell lines, induced pluripotent stem cells, kidney organoid cultures, and microfluidic devices enhance in vivo similarity. To this end, culture models aim to increase the proximal tubule epithelial phenotype, reconstitute multiple tissue compartments and extracellular matrix, allow exposure to fluid shear stress, and enable interaction between multiple cell types. Applying computation-aided end points and novel biomarkers to advanced culture models will further improve sensitivity and clinical relevance of in vitro drug-induced toxicity prediction. Implemented at the right stage of drug discovery and development and coupled to high-content evaluation techniques, these models have the potential to reduce attrition and aid the selection of candidate drugs with an appropriate safety profile.

Long-term flow through human intestinal organoids with the gut organoid flow chip (GOFlowChip)

Human intestinal organoids (HIOs) are millimeter-scale models of the human intestinal epithelium and hold tremendous potential for advancing fundamental and applied biomedical research. HIOs resemble the native gut in that they consist of a fluid-filled lumen surrounded by a polarized epithelium and associated mesenchyme; however, their topologically-closed, spherical shape prevents flow through the interior luminal space, making the system less physiological and leading to the buildup of cellular and metabolic waste. These factors ultimately limit experimentation inside the HIOs. Here, we present a millifluidic device called the gut organoid flow chip (GOFlowChip), which we use to "port" HIOs and establish steady-state liquid flow through the lumen for multiple days. This long-term flow is enabled by the use of laser-cut silicone gaskets, which allow liquid in the device to be slightly pressurized, suppressing bubble formation. To demonstrate the utility of the device, we establish separate luminal and extraluminal flow and use luminal flow to remove accumulated waste. This represents the first demonstration of established liquid flow through the luminal space of a gastrointestinal organoid over physiologically relevant time scales. Flow cytometry results reveal that HIO cell viability is unaffected by long-term porting and luminal flow. We expect the real-time, long-term control over luminal and extraluminal contents provided by the GOFlowChip will enable a wide variety of studies including intestinal secretion, absorption, transport, and co-culture with intestinal microorganisms.

In vitro metabolic activation of vitamin D3 by using a multi-compartment microfluidic liver-kidney organ on chip platform

Organ-on-chip platforms provide models that allow the representation of human physiological processes in cell-based miniaturized systems. Potential pre-clinical applications include drug testing and toxicity studies. Here we describe the use of a multi-compartment micro-fluidic chip to recapitulate hepatic vitamin D metabolism (vitamin D to 25-hydroxyvitamin D) and renal bio-activation (25-hydroxyvitamin D to 1,25-dihydroxyvitamin D) in humans. In contrast to cultivation in conventional tissue culture settings, on-chip cultivation of HepG2 and RPTEC cells in interconnected chambers, used to mimic the liver and kidneys, respectively, resulted in the enhanced expression of vitamin D metabolizing enzymes (CYP2R1, CYP27B1 and CYP24A1). Pump-driven flow of vitamin D3-containing medium through the microfluidic chip produced eluate containing vitamin D3 metabolites. LC-MSMS showed a strong accumulation of 25-hydroxyvitamin D. The chip eluate induced the expression of differentiation markers in HL-60 (acute myeloid leukemia) cells, assessed by qPCR and FACS analysis, in a manner similar to treatment with reference standards indicating the presence of fully activated 1,25 dihydroxyvitamin D, although the latter was not detected in the eluate by LC-MSMS. Interestingly, 25-hydroxyvitamin D by itself led to weak activation of HL-60 cells suggesting that 25-hydroxyvitamin D is also an active metabolite. Our experiments demonstrate that complex metabolic interactions can be reconstructed outside the human body using dedicated organ-on-chip platforms. We therefore propose that such systems may be used to mimic the in vivo metabolism of various micronutrients and xenobiotics.

Ex Vivo Tumor-on-a-Chip Platforms to Study Intercellular Interactions within the Tumor Microenvironment

The emergence of immunotherapies and recent FDA approval of several of them makes them a promising therapeutic strategy for cancer. While these advancements underscore the potential of engaging the immune system to target tumors, this approach has so far been efficient only for certain cancers. Extending immunotherapy as a widely acceptable treatment for various cancers requires a deeper understanding of the interactions of tumor cells within the tumor microenvironment (TME). The immune cells are a key component of the TME, which also includes other stromal cells, soluble factors, and extracellular matrix-based cues. While in vivo studies function as a gold standard, tissue-engineered microphysiological tumor models can offer patient-specific insights into cancer-immune interactions. These platforms, which recapitulate cellular and non-cellular components of the TME, enable a systematic understanding of the contribution of each component toward disease progression in isolation and in concert. Microfluidic-based microphysiological platforms recreating these environments, also known as "tumor-on-a-chip," are increasingly being utilized to study the effect of various elements of TME on tumor development. Herein are reviewed advancements in tumor-on-a-chip technology that are developed and used to understand the interaction of tumor cells with other surrounding cells, including immune cells, in the TME.

Kidney-on-a-chip: untapped opportunities

The organs-on-a-chip technology has shown strong promise in mimicking the complexity of native tissues in vitro and ex vivo, and recently significant advances have been made in applying this technology to studies of the kidney and its diseases. Individual components of the nephron, including the glomerulus, proximal tubule, and distal tubule/medullary collecting duct, have been successfully mimicked using organs-on-a-chip technology and yielding strong promises in advancing the field of ex vivo drug toxicity testing and augmenting renal replacement therapies. Although these models show promise over 2-dimensional cell systems in recapitulating important nephron features in vitro, nephron functions, such as tubular secretion, intracellular metabolism, and renin and vitamin D production, as well as prostaglandin synthesis are still poorly recapitulated in on-chip models. Moreover, construction of multiple-renal-components-on-a-chip models, in which various structures and cells of the renal system interact with each other, has remained a challenge. Overall, on-chip models show promise in advancing models of normal and pathological renal physiology, in predicting nephrotoxicity, and in advancing treatment of chronic kidney diseases.

Microfluidics in nanoparticle drug delivery; From synthesis to pre-clinical screening

Microfluidic technologies employ nano and microscale fabrication techniques to develop highly controllable and reproducible fluidic microenvironments. Utilizing microfluidics, lead compounds can be produced with the controlled physicochemical properties, characterized in a high-throughput fashion, and evaluated in in vitro biomimetic models of human organs; organ-on-a-chip. As a step forward from conventional in vitro culture methods, microfluidics shows promise in effective preclinical testing of nanoparticle-based drug delivery. This review presents a curated selection of state-of-the-art microfluidic platforms focusing on the fabrication, characterization, and assessment of nanoparticles for drug delivery applications. We also discuss the current challenges and future prospects of nanoparticle drug delivery development using microfluidics.

Advanced Microengineered Lung Models for Translational Drug Discovery

Lung diseases impose a significant socioeconomic burden and are a leading cause of morbidity and mortality worldwide. Moreover, respiratory medicine, unlike several other therapeutic areas, faces a disappointingly low number of new approved therapies. This is partly due to lack of reliable in vitro or in vivo models that can reproduce organ-level complexity and pathophysiological responses of human lung. Here, we examine new opportunities in application of recently emerged organ-on-chip technology to model human lung alveolus and small airway in preclinical drug development and biomarker discovery. We also discuss challenges that need to be addressed in coming years to further enhance the physiological and clinical relevance of these microsystems, enable their increased accessibility, and support their leap into personalized medicine.

Roles of fluid shear stress and retinoic acid in the differentiation of primary cultured human podocytes

Due to the distinct features that distinguish immortalized podocyte cell lines from their in vivo counterparts, primary cultured human podocytes might be a superior cell model for glomerular disease studies. However, the podocyte de-differentiation that occurs in culture remains an unresolved problem. Here, we present a method to differentiate primary cultured podocytes using retinoic acid (RA) and fluid shear stress (FSS), which mimic the in vivo environment of the glomerulus. RA treatment induced changes in the cell shape of podocytes from a cobblestone-like morphology to an arborized configuration with enhanced mobility. Moreover, the expression of synaptopodin and zonula occludens (ZO)-1 in RA-treated podocytes increased along with Krüppel-like factor 15 (KLF15) expression. Confocal microscopy revealed that RA increased the expression of cytoplasmic synaptopodin, which adopted a filamentous arrangement, and junctional ZO-1 expression, which showed a zipper-like pattern. To elucidate the effect of FSS in addition to RA, the podocytes were cultured in microfluidic devices and assigned to the static, static+RA, FSS, and FSS+RA groups. The FSS+RA group showed increased synaptopodin and ZO-1 expression with prominent spikes on the cell-cell interface. Furthermore, interdigitating processes were only observed in the FSS+RA group. Consistent with these data, the mRNA expression levels of synaptopodin, podocin, WT-1 and ZO-1 were synergistically increased by FSS and RA treatment. Additionally, the heights of the cells were greater in the FSS and FSS+RA groups than in the static groups, suggesting a restoration of the 3D cellular shape. Meanwhile, the expression of KLF15 increased in the RA-treated cells regardless of fluidic condition. Taken together, FSS and RA may contribute through different but additive mechanisms to the differentiation of podocytes. These cells may serve as a useful tool for mechanistic studies and the application of regenerative medicine to the treatment of kidney diseases.

From Microscale Devices to 3D Printing: Advances in Fabrication of 3D Cardiovascular Tissues

Current strategies for engineering cardiovascular cells and tissues have yielded a variety of sophisticated tools for studying disease mechanisms, for development of drug therapies, and for fabrication of tissue equivalents that may have application in future clinical use. These efforts are motivated by the need to extend traditional 2-dimensional (2D) cell culture systems into 3D to more accurately replicate in vivo cell and tissue function of cardiovascular structures. Developments in microscale devices and bioprinted 3D tissues are beginning to supplant traditional 2D cell cultures and preclinical animal studies that have historically been the standard for drug and tissue development. These new approaches lend themselves to patient-specific diagnostics, therapeutics, and tissue regeneration. The emergence of these technologies also carries technical challenges to be met before traditional cell culture and animal testing become obsolete. Successful development and validation of 3D human tissue constructs will provide powerful new paradigms for more cost effective and timely translation of cardiovascular tissue equivalents.

Microfabricated Physiological Models for In Vitro Drug Screening Applications

Microfluidics and microfabrication have recently been established as promising tools for developing a new generation of in vitro cell culture microdevices. The reduced amounts of reagents employed within cell culture microdevices make them particularly appealing to drug screening processes. In addition, latest advancements in recreating physiologically relevant cell culture conditions within microfabricated devices encourage the idea of using such advanced biological models in improving the screening of drug candidates prior to in vivo testing. In this review, we discuss microfluidics-based models employed for chemical/drug screening and the strategies to mimic various physiological conditions: fine control of 3D extra-cellular matrix environment, physical and chemical cues provided to cells and organization of co-cultures. We also envision future directions for achieving multi-organ microfluidic devices.

Nanomedicines for renal disease: current status and future applications

Treatment and management of kidney disease currently presents an enormous global burden, and the application of nanotechnology principles to renal disease therapy, although still at an early stage, has profound transformative potential. The increasing translation of nanomedicines to the clinic, alongside research efforts in tissue regeneration and organ-on-a-chip investigations, are likely to provide novel solutions to treat kidney diseases. Our understanding of renal anatomy and of how the biological and physico-chemical properties of nanomedicines (the combination of a nanocarrier and a drug) influence their interactions with renal tissues has improved dramatically. Tailoring of nanomedicines in terms of kidney retention and binding to key membranes and cell populations associated with renal diseases is now possible and greatly enhances their localization, tolerability, and efficacy. This Review outlines nanomedicine characteristics central to improved targeting of renal cells and highlights the prospects, challenges, and opportunities of nanotechnology-mediated therapies for renal diseases.

Kidney-on-a-chip technology for renal proximal tubule tissue reconstruction

The renal proximal tubule epithelium is responsible for active secretion of endogenous and exogenous waste products from the body and simultaneous reabsorption of vital compounds from the glomerular filtrate. The complexity of this transport machinery makes investigation of processes such as tubular drug secretion a continuous challenge for researchers. Currently available renal cell culture models often lack sufficient physiological relevance and reliability. Introducing complex biological culture systems in a 3D microfluidic design improves the physiological relevance of in vitro renal proximal tubule epithelium models. Organ-on-a-chip technology provides a promising alternative, as it allows the reconstruction of a renal tubule structure. These microfluidic systems mimic the in vivo microenvironment including multi-compartmentalization and exposure to fluid shear stress. Increasing data supports that fluid shear stress impacts the phenotype and functionality of proximal tubule cultures, for which we provide an extensive background. In this review, we discuss recent developments of kidney-on-a-chip platforms with current and future applications. The improved proximal tubule functionality using 3D microfluidic systems is placed in perspective of investigating cellular signalling that can elucidate mechanistic aberrations involved in drug-induced kidney toxicity.

Biology-inspired microphysiological system approaches to solve the prediction dilemma of substance testing

The recent advent of microphysiological systems - microfluidic biomimetic devices that aspire to emulate the biology of human tissues, organs and circulation in vitro - is envisaged to enable a global paradigm shift in drug development. An extraordinary US governmental initiative and various dedicated research programs in Europe and Asia have led recently to the first cutting-edge achievements of human single-organ and multi-organ engineering based on microphysiological systems. The expectation is that test systems established on this basis would model various disease stages, and predict toxicity, immunogenicity, ADME profiles and treatment efficacy prior to clinical testing. Consequently, this technology could significantly affect the way drug substances are developed in the future. Furthermore, microphysiological system-based assays may revolutionize our current global programs of prioritization of hazard characterization for any new substances to be used, for example, in agriculture, food, ecosystems or cosmetics, thus, replacing laboratory animal models used currently. Thirty-six experts from academia, industry and regulatory bodies present here the results of an intensive workshop (held in June 2015, Berlin, Germany). They review the status quo of microphysiological systems available today against industry needs, and assess the broad variety of approaches with fit-for-purpose potential in the drug development cycle. Feasible technical solutions to reach the next levels of human biology in vitro are proposed. Furthermore, key organ-on-a-chip case studies, as well as various national and international programs are highlighted. Finally, a roadmap into the future is outlined, to allow for more predictive and regulatory-accepted substance testing on a global scale.

Modeling Barrier Tissues In Vitro: Methods, Achievements, and Challenges

Organ-on-a-chip devices have gained attention in the field of in vitro modeling due to their superior ability in recapitulating tissue environments compared to traditional multiwell methods. These constructed growth environments support tissue differentiation and mimic tissue-tissue, tissue-liquid, and tissue-air interfaces in a variety of conditions. By closely simulating the in vivo biochemical and biomechanical environment, it is possible to study human physiology in an organ-specific context and create more accurate models of healthy and diseased tissues, allowing for observations in disease progression and treatment. These chip devices have the ability to help direct, and perhaps in the distant future even replace animal-based drug efficacy and toxicity studies, which have questionable relevance to human physiology. Here, we review recent developments in the in vitro modeling of barrier tissue interfaces with a focus on the use of novel and complex microfluidic device platforms.

Kidney-on-a-Chip Technology for Drug-Induced Nephrotoxicity Screening

Improved model systems to predict drug efficacy, interactions, and drug-induced kidney injury (DIKI) are crucially needed in drug development. Organ-on-a-chip technology is a suitable in vitro system because it reproduces the 3D microenvironment. A kidney-on-a-chip can mimic the structural, mechanical, transport, absorptive, and physiological properties of the human kidney. In this review we address the application of state-of-the-art microfluidic culturing techniques, with a focus on culturing kidney proximal tubules, that are promising for the detection of biomarkers that predict drug interactions and DIKI. We also discuss high-throughput screening and the challenges for in vitro to in vivo extrapolation (IVIVE) that will need to be overcome for successful implementation.

Microfluidic Organ/Body-on-a-Chip Devices at the Convergence of Biology and Microengineering

Recent advances in biomedical technologies are mostly related to the convergence of biology with microengineering. For instance, microfluidic devices are now commonly found in most research centers, clinics and hospitals, contributing to more accurate studies and therapies as powerful tools for drug delivery, monitoring of specific analytes, and medical diagnostics. Most remarkably, integration of cellularized constructs within microengineered platforms has enabled the recapitulation of the physiological and pathological conditions of complex tissues and organs. The so-called “organ-on-a-chip” technology, which represents a new avenue in the field of advanced in vitro models, with the potential to revolutionize current approaches to drug screening and toxicology studies. This review aims to highlight recent advances of microfluidic-based devices towards a body-on-a-chip concept, exploring their technology and broad applications in the biomedical field.

A Review of the Application of Body-on-a-Chip for Drug Test and Its Latest Trend of Incorporating Barrier Tissue

High-quality preclinical bioassay models are essential for drug research and development. We reviewed the emerging body-on-a-chip technology, which serves as a promising model to overcome the limitations of traditional bioassay models, and introduced existing models of body-on-a-chip, their constitutional details, application for drug testing, and individual features of these models. We put special emphasis on the latest trend in this field of incorporating barrier tissue into body-on-a-chip and discussed several remaining challenges of current body-on-a-chip.

Microfluidic Organ-on-a-Chip Technology for Advancement of Drug Development and Toxicology

In recent years, the exploitation of phenomena surrounding microfluidics has seen an increase in popularity, as researchers have found a way to use their unique properties to create superior design alternatives. One such application is representing the properties and functions of different organs on a microscale chip for the purpose of drug testing or tissue engineering. With the introduction of "organ-on-a-chip" systems, researchers have proposed various methods on various organ-on-a-chip systems to mimic their in vivo counterparts. In this article, a systematic approach is taken to review current technologies pertaining to organ-on-a-chip systems. Design processes with attention to the particular instruments, cells, and materials used are presented.

Investigation of ifosfamide and chloroacetaldehyde renal toxicity through integration of in vitro liver-kidney microfluidic data and pharmacokinetic-system biology models

We have integrated in vitro and in silico data to describe the toxicity of chloroacetaldehyde (CAA) on renal cells via its production from the metabolism of ifosfamide (IFO) by hepatic cells. A pharmacokinetic (PK) model described the production of CAA by the hepatocytes and its transport to the renal cells. A system biology model was coupled to the PK model to describe the production of reactive oxygen species (ROS) induced by CAA in the renal cells. In response to the ROS production, the metabolism of glutathione (GSH) and its depletion were modeled by the action of an NFE2L2 gene-dependent pathway. The model parameters were estimated in a Bayesian context via Markov Chain Monte Carlo (MCMC) simulations based on microfluidic experiments and literature in vitro data. Hepatic IFO and CAA in vitro intrinsic clearances were estimated to be 1.85 x 10(-9) μL s(-1) cell(-1) and 0.185 x 10(-9) μL s(-1) cell(-1) ,respectively (corresponding to an in vivo intrinsic IFO clearance estimate of 1.23 l h(-1) , to be compared to IFO published values ranging from 3 to 10 l h(-1) ). After model calibration, simulations made at therapeutic doses of IFO showed CAA renal intracellular concentrations ranging from 11 to 131 μM. Intracellular CAA concentrations above 70 μM induced intense ROS production and GSH depletion. Those responses were time and dose dependent, showing transient and non-linear kinetics. Those results are in agreement with literature data reporting that intracellular CAA toxic concentrations range from 35 to 320 μM, after therapeutic ifosfamide dosing. The results were also consistent with in vitro CAA renal cytotoxicity data.

Investigation of acetaminophen toxicity in HepG2/C3a microscale cultures using a system biology model of glutathione depletion

We have integrated in vitro and in silico information to investigate acetaminophen (APAP) and its metabolite N-acetyl-p-benzoquinone imine (NAPQI) toxicity in liver biochip. In previous works, we observed higher cytotoxicity of HepG2/C3a cultivated in biochips when exposed to 1 mM of APAP for 72 h as compared to Petri cultures. We complete our investigation with the present in silico approach to extend the mechanistic interpretation of the intracellular kinetics of the toxicity process. For that purpose, we propose a mathematical model based on the coupling of a drug pharmacokinetic model (PK) with a systemic biology model (SB) describing the reactive oxygen species (ROS) production by NAPQI and the subsequent glutathione (GSH) depletion. The SB model was parameterized using (i) transcriptomic data, (ii) qualitative results of time lapses ROS fluorescent curves for both control and 1-mM APAP-treated experiments, and (iii) additional GSH literature data. The PK model was parameterized (i) using the in vitro kinetic data (at 160 μM, 1 mM, 10 mM), (ii) using the parameters resulting from a physiologically based pharmacokinetic (PBPK) literature model for APAP, and (iii) by literature data describing NAPQI formation. The PK-SB model predicted a ROS increase and GSH depletion due to the NAPQI formation. The transition from a detoxification phase and NAPQI and ROS accumulation was predicted for a NAPQI concentration ranging between 0.025 and 0.25 μM in the cytosol. In parallel, we performed a dose response analysis in biochips that shows a reduction of the final hepatic cell number appeared in agreement with the time and doses associated with the switch of the NAPQI detoxification/accumulation. As a result, we were able to correlate in vitro extracellular APAP exposures with an intracellular in silico ROS accumulation using an integration of a coupled mathematical and experimental liver on chip approach.

Microfluidic organs-on-chips

An organ-on-a-chip is a microfluidic cell culture device created with microchip manufacturing methods that contains continuously perfused chambers inhabited by living cells arranged to simulate tissue- and organ-level physiology. By recapitulating the multicellular architectures, tissue-tissue interfaces, physicochemical microenvironments and vascular perfusion of the body, these devices produce levels of tissue and organ functionality not possible with conventional 2D or 3D culture systems. They also enable high-resolution, real-time imaging and in vitro analysis of biochemical, genetic and metabolic activities of living cells in a functional tissue and organ context. This technology has great potential to advance the study of tissue development, organ physiology and disease etiology. In the context of drug discovery and development, it should be especially valuable for the study of molecular mechanisms of action, prioritization of lead candidates, toxicity testing and biomarker identification.

First pass intestinal and liver metabolism of paracetamol in a microfluidic platform coupled with a mathematical modeling as a means of evaluating ADME processes in humans

We developed a microfluidic platform to investigate paracetamol intestinal and liver first pass metabolism. This approach was coupled with a mathematical model to estimate intrinsic in vitro parameters and to predict in vivo processes. The kinetic modeling estimated the paracetamol and paracetamol sulfate permeabilities, the sulfate and glucuronide effluxes in the intestine compartment. Based on a gut model, we estimated intrinsic intestinal clearance of between 26 and 77 L/h for paracetamol in humans, a permeability of 10 L/h, and a gut availability between 0.17 and 0.53 (compared to 0.95-1 in vivo). The role played by the liver in paracetamol metabolism was estimated via in vitro intrinsic clearances of 7.6, 13.6, and 11.5 µL/min/10(6) cells for HepG2/C3a, rat primary hepatocytes, and human primary hepatocytes, respectively. Based on a parallel tube model to describe the liver, the paracetamol hepatic clearance, and the paracetamol hepatic availability in humans were estimated at 6.5 mL/min/kg of bodyweight (BDW) and 0.7, respectively (when compared to 5 mL/min/kg of BDW and 0.77 to 0.88 for in vivo values, respectively). The drug availability was predicted ranging between 0.24 and 0.41 (0.88 in vivo). The overall approach provided a first step in an integrated strategy combining in silico/in vitro methods based on microfluidic for evaluating drug absorption, distribution and metabolism processes.

Integration of pharmacokinetic and NRF2 system biology models to describe reactive oxygen species production and subsequent glutathione depletion in liver microfluidic biochips after flutamide exposure

We present a systems biology analysis of rat primary hepatocytes response after exposure to 10 μM and 100 μM flutamide in liver microfluidic biochips. We coupled an in vitro pharmacokinetic (PK) model of flutamide to a system biology model of its reactive oxygen species (ROS) production and scavenging by the Nrf2 regulated glutathione production. The PK model was calibrated using data on flutamide kinetics, hydroxyflutamide and glutathione conjugates formation in microfluidic conditions. The parameters of Nrf2-related gene activities and the subsequent glutathione depletion were calibrated using microarray data from our microfluidic experiments and literature information. Following a 10 μM flutamide exposure, the model predicted a recovery time to baseline levels of glutathione (GSH) and ROS in agreement with our experimental observations. At 100 μM, the model predicted that metabolism saturation led to an important accumulation of flutamide in cells, a high ROS production and complete GSH depletion. The high levels of ROS predicted were consistent with the necrotic switch observed by transcriptomics, and the high cell mortality we had experimentally observed. The model predicted a transition between recoverable GSH depletion and deep GSH depletion at about 12.5 μM of flutamide (single perfusion exposure). Our work shows that in vitro biochip experiments can provide supporting information for complex in silico modeling including data from extra cellular and intra cellular levels. We believe that this approach can be an efficient strategy for a global integrated methodology in predictive toxicology.

A modified TALEN-based strategy for rapidly and efficiently generating knockout mice for kidney development studies

The transcription activator-like effector nucleases (TALENs) strategy has been widely used to delete and mutate genes in vitro. This strategy has begun to be used for in vivo systemic gene manipulation, but not in an organ-specific manner. In this study, we developed a modified, highly efficient TALEN strategy using a dual-fluorescence reporter. We used this modified strategy and, within 5 weeks, we successfully generated kidney proximal tubule-specific gene Ttc36 homozygous knockout mice. Unilateral nephrectomy was performed on the 6-week-old founders (F0) to identify the knockout genotype prior to the birth of the offspring. This strategy was found to have little effect on reproduction in the knockout mice and inheritability of the knockout genotypes. The modified TALEN knockout strategy in combination with unilateral nephrectomy can be readily used for studies of gene function in kidney development and diseases.

Enhancement of renal epithelial cell functions through microfluidic-based coculture with adipose-derived stem cells

Current hemodialysis has functional limitations and is insufficient for renal transplantation. The bioartificial tubule device has been developed to contribute to metabolic functions by implanting renal epithelial cells into hollow tubes and showed a higher survival rate in acute kidney injury patients. In healthy kidney, epithelial cells are surrounded by various types of cells that interact with extracellular matrices, which are primarily composed of laminin and collagen. The current study developed a microfluidic coculture platform to enhance epithelial cell function in bioartificial microenvironments with multiple microfluidic channels that are microfabricated by polydimethylsiloxane. Collagen gel (CG) encapsulated with adipose-derived stem cells (CG-ASC) was injected into a central microfluidic channel for three-dimensional (3D) culture. The resuspended Madin-Darby canine kidney (MDCK) cells were injected into nascent channels and formed an epithelial monolayer. In comparison to coculture different cells using the commercial transwell system, the current coculture device allowed living cell monitoring of both the MDCK epithelial monolayer and CG-ASC in a 3D microenvironment. By coculture with CG-ASC, the cell height was increased with columnar shapes in MDCK. Promotion of cilia formation and functional expression of the ion transport protein in MDCK were also observed in the cocultured microfluidic device. When applying fluid flow, the intracellular protein dynamics can be monitored in the current platform by using the time-lapse confocal microscopy and transfection of GFP-tubulin plasmid in MDCK. Thus, this microfluidic coculture device provides the renal epithelial cells with both morphological and functional improvements that may avail to develop bioartificial renal chips.

Investigation of ifosfamide nephrotoxicity induced in a liver-kidney co-culture biochip

In this article, we present a liver-kidney co-culture model in a micro fluidic biochip. The liver was modeled using HepG2/C3a and HepaRG cell lines and the kidney using MDCK cell lines. To demonstrate the synergic interaction between both organs, we investigated the effect of ifosfamide, an anticancerous drug. Ifosfamide is a prodrug which is metabolized by the liver to isophosforamide mustard, an active metabolite. This metabolism process also leads to the formation of chloroacetaldehyde, a nephrotoxic metabolite and acrolein a urotoxic one. In the biochips of MDCK cultures, we did not detect any nephrotoxic effects after 72 h of 50 µM ifosfamide exposure. However, in the liver-kidney biochips, the same 72 h exposure leads to a nephrotoxicity illustrated by a reduction of the number of MDCK cells (up to 30% in the HepaRG-MDCK) when compared to untreated co-cultures or treated MDCK monocultures. The reduction of the MDCK cell number was not related to a modification of the cell cycle repartition in ifosfamide treated cases when compared to controls. The ifosfamide biotransformation into 3-dechloroethylifosfamide, an equimolar byproduct of the chloroacetaldehyde production, was detected by mass spectrometry at a rate of apparition of 0.3 ± 0.1 and 1.1 ± 0.3 pg/h/biochips in HepaRG monocultures and HepaRG-MDCK co-cultures respectively. Any metabolite was detected in HepG2/C3a cultures. Furthermore, the ifosfamide treatment in HepaRG-MDCK co-culture system triggered an increase in the intracellular calcium release in MDCK cells on contrary to the treatment on MDCK monocultures. As 3-dechloroethylifosfamide is not toxic, we have tested the effect of equimolar choloroacetaldehyde concentration onto the MDCK cells. At this concentration, we found a quite similar calcium perturbation and MDCK nephrotoxicity via a reduction of 30% of final cell numbers such as in the ifosfamide HepaRG-MDCK co-culture experiments. Our results suggest that ifosfamide nephrotoxicity in a liver-kidney micro fluidic co-culture model using HepaRG-MDCK cells is induced by the metabolism of ifosfamide into chloroacetaldehyde whereas this pathway is not functional in HepG2/C3a-MDCK model. This study demonstrates the interest in the development of systemic organ-organ interactions using micro fluidic biochips. It also illustrated their potential in future predictive toxicity model using in vitro models as alternative methods.