Predicting tubular reabsorption with a human kidney proximal tubule tissue-on-a-chip and physiologically-based modeling

A perfused iPSC-derived proximal tubule model for predicting drug-induced kidney injury

The kidney is frequently exposed to high levels of drugs and their metabolites, which can injure the kidney and the proximal tubule (PT) in particular. In order to detect nephrotoxicity early during drug development, relevant in vitro models are essential. Here, we introduce a robust and versatile cell culture insert-based iPSC-derived PT model, which can be maintained in a microphysiological system for at least ten days. We demonstrate the model's ability to predict drug-induced PT injury using polymyxin B, cyclosporin A, and cisplatin, and observe that perfusion distinctly impacts our model's response to xenobiotics. We observe that the upregulation of metallothioneins that is described in vivo after treatment with these drugs is reliably detected in dynamic, but not static in vitro PT models. Finally, we use our model to alleviate polymyxin-induced nephrotoxicity by supplementing the antioxidant curcumin. Together, these findings illustrate that our perfused iPSC-derived PT model is versatile and well-suited for in vitro studies investigating nephrotoxicity and its prevention. Reliable and user-friendly in vitro models like this enable the early detection of nephrotoxic potential, thereby minimizing adverse effects and reducing drug attrition.

A comparative review of organ-on-a-chip technologies for micro- and nanoplastics versus other environmental toxicants

In recent years, organ-on-a-chip (OOC) technology has emerged as a groundbreaking platform to simulate complex physiological processes. Concurrently, the global presence of micro and nano-plastics (MNPs) in the environment and their ingestion has raised concerns about their impact on human health, specifically organs such as the lungs, liver, kidneys, and blood vessels. There is an added concern about their ability to cross even the blood-brain barrier (BBB). While numerous papers have been published assessing various environmental toxicants with OOCs, those for MNPs are relatively small. To ascertain current trends in methodologies and catalog the types of toxicants explored, we have gathered and analyzed papers that used OOCs to assess various environmental toxicants' impacts on these organs. Various platforms assessing MNPs were analyzed and compared to those for other environmental toxicants. Our results show that few articles have been published that used OOCs to assess MNPs' toxicity to human organs. Specifically, certain organs, such as the heart and skin, have little representation in this collection. OOC-based evaluation methods for MNP's toxicity have many advantages over the current methods - in vitro tests with 2D human cell cultures and animal studies - including lower cost, faster results, and greater physiological relevance. This review summarizes the current OOC techniques for assessing environmental toxicants and laboratory methods for evaluating MNPs' toxicity to humans. A systematic comparison of these methods provides a deeper understanding of the current techniques and suggests the optimized use of OOCs for assessing MNPs' and other pollutants' toxicity.

Decoupling shear stress and pressure effects in the biomechanics of autosomal dominant polycystic kidney disease using a perfused kidney-on-chip

Kidney tubular cells are submitted to two distinct mechanical forces generated by the urine flow: shear stress and hydrostatic pressure. In addition, the mechanical properties of the surrounding extracellular matrix modulate tubule deformation under constraints. These mechanical factors likely play a role in the pathophysiology of kidney as exemplified by autosomal dominant polycystic kidney disease, in which pressure, flow and matrix stiffness have been proposed to modulate the cystic dilation of tubules with PKD1 mutations. The lack of in vitro systems recapitulating the mechanical environment of kidney tubules impedes our ability to dissect the role of these mechanical factors. Here we describe a perfused kidney-on-chip with tunable extracellular matrix mechanical properties and hydrodynamic constraints, that allows a decoupling of shear stress and flow. We used this system to dissect how these mechanical cues affect Pkd1-/- tubule dilation. We investigated cell behavior for a flow shear stress of 1 dyn/cm², combined or not with a 10-mbar intraluminal pressure. Our results showed two distinct mechanisms leading to tubular dilation. For Pkd1-/- PCT cells (proximal tubule), overproliferation mechanically leads to tubular dilation of 1.5-2-fold in 5 days, regardless of the mechanical context. For mIMCD-3 cells (collecting duct), tube dilation was associated with a squamous cell morphology but not with overproliferation and was highly sensitive to extracellular matrix properties, with suppression of the dilation when switching extracellular matrix composition from 6 to 9 mg/ml collagen. Contrary to PCT, mIMCD-3 tube dilation was highly sensitive to the nature of hydrodynamic constraint. Surprisingly, flow alone suppressed Pkd1-/- mIMCD-3 tubule dilation observed in static conditions, while the addition of luminal pressure restored it. Our in vitro model emulating nephron geometrical and mechanical organization sheds light on the roles of mechanical constraints in ADPKD and demonstrates the importance of controlling intraluminal pressure in kidney tubule models. STATEMENT OF SIGNIFICANCE: In autosomal dominant polycystic kidney disease, the development of numerous renal cysts leads to renal failure, with no curative therapy available. The initial stage of cyst formation, local tubule dilation, remains poorly understood. Although mechanical cues may be decisive, there is a lack of biomimetic systems recapitulating them. Here, an innovative kidney-on-a-chip was designed to decouple different hydrodynamic cues. We observed disease-specific tube dilation, driven by distinct mechanisms based or not on proliferation, in proximal tubule or collecting duct cell lines. Strikingly in the latter case, dilation, highly dependent on mechanical conditions, was suppressed by flow but restored by luminal pressure. Our model highlights the role of mechanical constraints in ADPKD and the importance of pressure control in renal models.

Application progress of bio-manufacturing technology in kidney organoids

Kidney transplantation remains a pivotal treatment modality for kidney disease, yet its progress is significantly hindered by the scarcity of donor kidneys and ethical dilemmas surrounding their procurement. As organoid technology evolves and matures, the creation of bionic human kidney organoids offers profound potential for advancing kidney disease research, drug nephrotoxicity screening, and regenerative medicine. Nevertheless, current kidney organoid models grapple with limitations such as constrained cellular differentiation, underdeveloped functional structures, and a crucial absence of vascularization. This deficiency in vascularization, in particular, stunts organoid development, restricts their size, diminishes filtration capabilities, and may trigger immune inflammatory reactions through the resulting ischemic microenvironment. Hence, the achievement of vascularization within kidney organoids and the successful establishment of functional microvascular networks constitutes a paramount goal for their future progression. In this review, we provide an overview of recent advancements in biotechnology domains, encompassing organ-on-a-chip technology, biomimetic matrices, and bioprinting, with the aim of catalyzing technological breakthroughs that can enhance the vascularization of kidney organoids and broaden their applicability. These technologies hold the key to unlocking the full potential of kidney organoids as a transformative therapeutic option for kidney disease.

Comparative Analysis of Proximal Tubule Cell Sources for In Vitro Studies of Renal Proximal Tubule Toxicity

Background/Objectives: The kidneys are essential for eliminating drugs and chemicals from the human body and renal epithelial cells are particularly vulnerable to damage caused by xenobiotics and their metabolites. Drug-induced kidney toxicity is a major cause of drug attrition during preclinical and clinical development and the ability to predict renal toxicity remains a pressing challenge, necessitating more predictive in vitro models. However, the abundance of commercially available renal proximal tubule epithelial cell (RPTEC) sources complicates the selection of the most predictive cell types. Methods: This study compared a wide range of RPTEC sources, including primary cells (Lonza) and various RPTEC lines from different vendors, such as ciPTECs (Cell4Pharma), TERT1/RPTECs (ATCC), and HEK293 (GenoMembrane), including OAT1-overexpressing variants. HepG2 cells were included for a comparison of organ specificity. The different cells were cultured in 96- or 384-well plates and exposed to 12 drugs for 72 h at a concentration yielding a response (0.3-300 µM) to evaluate their ability to predict clinical outcomes. The CellTiterGlo® assay was used to measure cell viability, and transcriptome data from unexposed cells was analyzed using the TempO-seq® S1500+ platform. Results: Gene expression data showed that the primary kidney cells most closely matched the transcriptome of the human kidney medulla, followed by the TERT1 and ciPTEC lines, with the HEK lines showing the lowest similarity. The RPTEC sources showed clustering by cell type, with OAT1 overexpression driving changes in metabolic, detoxification, and immune pathways, especially in TERT1 cells. Cell viability data were used to determine points of departure (PODs) which were compared to human serum Cmax values to assess safety margins. The TERT1 and ciPTEC RPTEC lines demonstrated the highest predictive performance for nephrotoxicity, with OAT1 overexpression significantly enhancing sensitivity, accuracy, and overall predictive power (MCC scores: 0.764 and 0.667, respectively). In contrast, HepG2 cells showed the lowest performance across all metrics, highlighting the critical role of cell type and transporter expression in nephrotoxicity prediction. Conclusions: This study highlights important differences among RPTEC sources and their utility in drug safety studies of the renal proximal tubule. We show that while improved cell options for renal proximal tubule are needed, OAT1-overexpressing RPTECs are a superior model to the background cell type.

Comparative analysis of the physiological and transport functions of various sources of renal proximal tubule cells under static and fluidic conditions in PhysioMimix T12 platform

In vitro models that can faithfully replicate critical aspects of kidney tubule function such as directional drug transport are in high demand in pharmacology and toxicology. Accordingly, development and validation of new models is underway. The objective of this study was to characterize physiologic and transport functions of various sources of human renal proximal tubule epithelial cells (RPTECs). We tested telomerase reverse transcriptase 1 (TERT1)-immortalized RPTECs, including organic anion transporter 1 (OAT1)-, organic cation transporter 2 (OCT2)-, or OAT3-overexpressing variants and primary RPTECs. Cells were cultured on transwell membranes in static (24-well transwells) and fluidic (transwells in PhysioMimix T12 organ-on-chip with 2 μL/s flow) conditions. Barrier formation, transport, and gene expression were evaluated. We show that 2 commercially available primary RPTECs were not suitable for studies of directional transport on transwells because they formed a substandard barrier even though they exhibited higher expression of transporters, especially under flow. TERT1-parent, -OAT1, and -OAT3 cells formed robust barriers but were unaffected by flow. TERT1-OAT1 cells exhibited inhibitable para-aminohippurate transport that was enhanced by flow. However, efficient tenofovir secretion and perfluorooctanoic acid reabsorption by TERT1-OAT1 cells were not modulated by flow. Gene expression showed that TERT1 and TERT1-OAT1 cells were more correlated with human kidney than other cell lines but that flow did not have noticeable effects. Overall, our data show that addition of flow to in vitro studies of the renal proximal tubule may afford benefits in some aspects of modeling kidney function but that careful consideration of the impact such adaptations would have on the cost and throughput of the experiments is needed. SIGNIFICANCE STATEMENT: The topic of reproducibility and robustness of complex microphysiological systems is looming large in the field of biomedical research; therefore, uptake of these new models by the end-users is slow. This study systematically compared various renal proximal tubule epithelial cell sources and experimental conditions, aiming to identify the level of model complexity needed for testing renal tubule transport. We demonstrate that although tissue chips may afford some benefits, their throughput and complexity need careful consideration in each context of use.

Evaluating nephrotoxicity reduction in a novel polymyxin B formulation: insights from a 3D kidney-on-a-chip model

This study aimed to assess the nephrotoxicity associated with VRP-034 (novel formulation of polymyxin B [PMB]) compared to marketed PMB in a three-dimensional (3D) kidney-on-a-chip model. To model the human kidney proximal tubule for analysis, tubular structures were established using 23 triple-channel chips seeded with RPTEC/hTERT1 cells. These cells were exposed to VRP-034 or PMB at seven concentrations (1-200 µM) over 12, 24, and 48 h. A suite of novel kidney injury biomarkers, cell health, and inflammatory markers were quantitatively assessed in the effluent. Additionally, caspase and cytochrome C levels were measured, and cell viability was evaluated using calcein AM and ethidium homodimer-1 (EthD-1). Exposure to marketed PMB resulted in significantly elevated levels (P < 0.05) of four key biomarkers (KIM-1, cystatin C, clusterin, and OPN) compared to VRP-034, particularly at clinically relevant concentrations of ≥10 µM. At 25 µM, all biomarkers demonstrated a significant increase (P < 0.05) with marketed PMB exposure compared to VRP-034. Inflammatory markers (interleukin-6 and interleukin-8) increased significantly (P < 0.05) with marketed PMB at concentrations of ≥5 µM, relative to VRP-034. VRP-034 displayed superior cell health outcomes, exhibiting lower lactate dehydrogenase release, while ATP levels remained comparable. Morphological analysis revealed that marketed PMB induced more severe damage, disrupting tubular integrity. Both treatments activated cytochrome C, caspase-3, caspase-8, caspase-9, and caspase-12 in a concentration-dependent manner; however, caspase activation was significantly reduced (P < 0.05) with VRP-034. This study demonstrates that VRP-034 significantly reduces nephrotoxicity compared to marketed PMB within a 3D microphysiological system, suggesting its potential to enable the use of full therapeutic doses of PMB with an improved safety profile, addressing the need for less nephrotoxic polymyxin antibiotics.

Complexin vitromodels positioned for impact to drug testing in pharma: a review

Recent years have seen the creation and popularization of various complexin vitromodels (CIVMs), such as organoids and organs-on-chip, as a technology with the potential to reduce animal usage in pharma while also enhancing our ability to create safe and efficacious drugs for patients. Public awareness of CIVMs has increased, in part, due to the recent passage of the FDA Modernization Act 2.0. This visibility is expected to spur deeper investment in and adoption of such models. Thus, end-users and model developers alike require a framework to both understand the readiness of current models to enter the drug development process, and to assess upcoming models for the same. This review presents such a framework for model selection based on comparative -omics data (which we term model-omics), and metrics for qualification of specific test assays that a model may support that we term context-of-use (COU) assays. We surveyed existing healthy tissue models and assays for ten drug development-critical organs of the body, and provide evaluations of readiness and suggestions for improving model-omics and COU assays for each. In whole, this review comes from a pharma perspective, and seeks to provide an evaluation of where CIVMs are poised for maximum impact in the drug development process, and a roadmap for realizing that potential.

Advanced Kidney Models In Vitro Using the Established Cell Line Renal Proximal Tubular Epithelial/Telomerase Reverse Transcriptase1 for Nephrotoxicity Assays

Nephrotoxicity stands as one of the most limiting effects in the development and validation of new drugs. The kidney, among the organs evaluated in toxicity assessments, has a higher susceptibility, with nephrotoxic potential frequently evading detection until late in clinical trials. Traditional cell culture, which has been widely used for decades, does not recapitulate the structure and complexity of the native tissue, which can affect cell function, and the response to cytotoxins does not resemble what occurs in the kidney. In the current study, we aimed to address these challenges by creating in vitro kidney models that faithfully biomimic the dynamics of the renal proximal tubule, using the well-established RPTEC/TERT1 cell line. For doing so, two models were developed, one recreating tubule-like structures (2.5D model) and the other using microfluidic technology (kidney-on-a-chip). The 2.5D model allowed tubular structures to be generated in the absence of hydrogels, and the kidney-on-a-chip model allowed shear stress to be applied to the cell culture, which is a physiological stimulus in the renal tissue. After characterization of both models, different nephrotoxic compounds such as cisplatin, tacrolimus, and daunorubicin were used to study cell responses after treatment. The developed models in our study could be a valuable tool for pre-clinical nephrotoxic testing of drugs and new compounds.

Bridging barriers: advances and challenges in modeling biological barriers and measuring barrier integrity in organ-on-chip systems

Biological barriers such as the blood-brain barrier, skin, and intestinal mucosal barrier play key roles in homeostasis, disease physiology, and drug delivery - as such, it is important to create representative in vitro models to improve understanding of barrier biology and serve as tools for therapeutic development. Microfluidic cell culture and organ-on-a-chip (OOC) systems enable barrier modelling with greater physiological fidelity than conventional platforms by mimicking key environmental aspects such as fluid shear, accurate microscale dimensions, mechanical cues, extracellular matrix, and geometrically defined co-culture. As the prevalence of barrier-on-chip models increases, so does the importance of tools that can accurately assess barrier integrity and function without disturbing the carefully engineered microenvironment. In this review, we first provide a background on biological barriers and the physiological features that are emulated through in vitro barrier models. Then, we outline molecular permeability and electrical sensing barrier integrity assessment methods, and the related challenges specific to barrier-on-chip implementation. Finally, we discuss future directions in the field, as well important priorities to consider such as fabrication costs, standardization, and bridging gaps between disciplines and stakeholders.

Biomimetic microfluidic chips for toxicity assessment of environmental pollutants

Various types of pollutants widely present in environmental media, including synthetic and natural chemicals, physical pollutants such as radioactive substances, ultraviolet rays, and noise, as well as biological organisms, pose a huge threat to public health. Therefore, it is crucial to accurately and effectively explore the human physiological responses and toxicity mechanisms of pollutants to prevent diseases caused by pollutants. The emerging toxicological testing method biomimetic microfluidic chips (BMCs) exhibit great potential in environmental pollutant toxicity assessment due to their superior biomimetic properties. The BMCs are divided into cell-on-chips and organ-on-chips based on the distinctions in bionic simulation levels. Herein, we first summarize the characteristics, emergence and development history, composition and structure, and application fields of BMCs. Then, with a focus on the toxicity mechanisms of pollutants, we review the applications and advances of the BMCs in the toxicity assessment of physical, chemical, and biological pollutants, respectively, highlighting its potential and development prospects in environmental toxicology testing. Finally, the opportunities and challenges for further use of BMCs are discussed.

A new tissue-agnostic microfluidic device to model physiology and disease: the lattice platform

To accurately phenocopy human biology in vitro, researchers have been reducing their dependence on standard, static two-dimensional (2D) cultures and instead are moving towards three-dimensional (3D) and/or multicellular culture techniques. While these culture innovations are becoming more commonplace, there is a growing body of research that illustrates the benefits and even necessity of recapitulating the dynamic flow of nutrients, gas, waste exchange and tissue interactions that occur in vivo. However, cost and engineering complexity are two main factors that hinder the adoption of these technologies and incorporation into standard laboratory workflows. We developed LATTICE, a plug-and-play microfluidic platform able to house up to eight large tissue or organ models that can be cultured individually or in an interconnected fashion. The functionality of the platform to model both healthy and diseased tissue states was demonstrated using 3D cultures of reproductive tissues including murine ovarian tissues and human fallopian tube explants (hFTE). When exogenously exposed to pathological doses of gonadotropins and androgens to mimic the endocrinology of polycystic ovarian syndrome (PCOS), subsequent ovarian follicle development, hormone production and ovulation copied key features of this endocrinopathy. Further, hFTE cilia beating decreased significantly only when experiencing continuous media exchanges. We were then able to endogenously recreate this phenotype on the platform by dynamically co-culturing the PCOS ovary and hFTE. LATTICE was designed to be customizable with flexibility in 3D culture formats and can serve as a powerful automated tool to enable the study of tissue and cellular dynamics in health and disease in all fields of research.

Organ-on-chip systems as a model for nanomedicine

Nanomedicine is giving rise to increasing numbers of successful drugs, including cancer treatments, molecular imaging agents, and novel vaccine formulations. However, traditionally available model systems offer limited clinical translation and, compared to the number of preclinical studies, the approval rate of nanoparticles (NPs) for clinical use remains disappointingly low. A new paradigm of modeling biological systems on microfluidic chips has emerged in the last decade and is being gradually adopted by the nanomedicine community. These systems mimic tissues, organs, and diseases like cancer, on devices with small physical footprints and complex geometries. In this review, we report studies that used organ-on-chip approaches to study the interactions of NPs with biological systems. We present examples of NP toxicity studies, studies using biological NPs such as viruses, as well as modeling biological barriers and cancer on chip. Organ-on-chip systems present an exciting opportunity and can provide a renewed direction for the nanomedicine community.

Semisynthesis, Biological Evaluation and Molecular Docking Studies of Barbatic Acid Derivatives as Novel Diuretic Candidates

Barbatic acid, a compound isolated from lichen, has demonstrated a variety of biological activities. In this study, a series of esters based on barbatic acid (6a-q') were designed, synthesized, and evaluated for their diuretic and litholytic activity at a concentration of 100 μmol/L in vitro. All target compounds were characterized using ¹H NMR, ¹³C NMR, and HRMS, and the spatial structure of compound 6w was confirmed using X-ray crystallography. The biological results showed that some derivatives, including 6c, 6b', and 6f', exhibited potent diuretic activity, and 6j and 6m displayed promising litholytic activity. Molecular docking studies further suggested that 6b' had an optimal binding affinity to WNK1 kinases related to diuresis, while 6j could bind to the bicarbonate transporter CaSR through a variety of forces. These findings indicate that some barbatic acid derivatives could be further developed into novel diuretic agents.

A glomerulus and proximal tubule microphysiological system simulating renal filtration, reabsorption, secretion, and toxicity

Microphysiological systems (MPS) are powerful predictive tools for assessing drug-induced kidney injuries. Previous MPS have examined single regions of the nephron, but lack simultaneous filtration, reabsorption, and secretion functionality. Here, we developed a partially open MPS that structurally and functionally recapitulated the glomerular filtration barrier, proximal tubular reabsorption, and secretion for seven days. The system introduced a recirculation circuit and an open filtrate output as a source of functional testing. As a proof-of-concept, a tri-culture of immortalized podocytes, umbilical vein endothelial cells, and proximal tubule (PCT) cells were housed in a single MPS: T-junction, glomerulus housing unit, and PCT chip. The MPS successfully retained blood serum protein, reabsorbed glucose, secreted creatinine, and expressed cell-type specific proteins (VE-cadherin, nephrin, and ZO-1). To simulate drug-induced kidney injuries, the system was perfused with cisplatin and adriamycin, and then tested using serum albumin filtration, glucose clearance, and lactate dehydrogenase release. The glomerulus and PCT MPS demonstrated a complex, dynamic microenvironment and recreated some in vivo-like functions in basal and drug-induced conditions, offering a novel prototype for preclinical testing.

Plant vs. Kidney: Evaluating Nephrotoxicity of Botanicals with the Latest Toxicological Tools

Botanicals can cause nephrotoxicity via numerous mechanisms, including disrupting renal blood flow, damaging compartments along the nephron, and obstructing urinary flow. While uncommon, there are various reports of botanical-induced nephrotoxicity in the literature, such as from aristolochia (Aristolochia spp.) and rhubarb (Rheum spp.). However, at present, it is a challenge to assess the toxic potential of botanicals because their chemical composition is variable due to factors such as growing conditions and extraction techniques. Therefore, selecting a single representative sample for an in vivo study is difficult. Given the increasing use of botanicals as dietary supplements and herbal medicine, new approach methodologies (NAMs) are needed to evaluate the potential for renal toxicity to ensure public safety. Such approaches include in vitro models that use layers of physiological complexity to emulate the in vivo microenvironment, enhance the functional viability and differentiation of cell cultures, and improve sensitivity to nephrotoxic insults. Furthermore, computational tools such as physiologically based pharmacokinetic (PBPK) modeling can add confidence to these tools by simulating absorption, distribution, metabolism, and excretion. The development and implementation of NAMs for renal toxicity testing will allow specific mechanistic data to be generated, leading to a better understanding of the nephrotoxic potential of botanicals.

Biomedical Applications of Microfluidic Devices: A Review

Both passive and active microfluidic chips are used in many biomedical and chemical applications to support fluid mixing, particle manipulations, and signal detection. Passive microfluidic devices are geometry-dependent, and their uses are rather limited. Active microfluidic devices include sensors or detectors that transduce chemical, biological, and physical changes into electrical or optical signals. Also, they are transduction devices that detect biological and chemical changes in biomedical applications, and they are highly versatile microfluidic tools for disease diagnosis and organ modeling. This review provides a comprehensive overview of the significant advances that have been made in the development of microfluidics devices. We will discuss the function of microfluidic devices as micromixers or as sorters of cells and substances (e.g., microfiltration, flow or displacement, and trapping). Microfluidic devices are fabricated using a range of techniques, including molding, etching, three-dimensional printing, and nanofabrication. Their broad utility lies in the detection of diagnostic biomarkers and organ-on-chip approaches that permit disease modeling in cancer, as well as uses in neurological, cardiovascular, hepatic, and pulmonary diseases. Biosensor applications allow for point-of-care testing, using assays based on enzymes, nanozymes, antibodies, or nucleic acids (DNA or RNA). An anticipated development in the field includes the optimization of techniques for the fabrication of microfluidic devices using biocompatible materials. These developments will increase biomedical versatility, reduce diagnostic costs, and accelerate diagnosis time of microfluidics technology.

Microphysiological Systems Evaluation: Experience of TEX-VAL Tissue Chip Testing Consortium

Much has been written and said about the promise and excitement of microphysiological systems, miniature devices that aim to recreate aspects of human physiology on a chip. The rapid explosion of the offerings and persistent publicity placed high expectations on both product manufacturers and regulatory agencies to adopt the data. Inevitably, discussions of where this technology fits in chemical testing paradigms are ongoing. Some end-users became early adopters, whereas others have taken a more cautious approach because of the high cost and uncertainties of their utility. Here, we detail the experience of a public-private collaboration established for testing of diverse microphysiological systems. Collectively, we present a number of considerations on practical aspects of using microphysiological systems in the context of their applications in decision-making. Specifically, future end-users need to be prepared for extensive on-site optimization and have access to a wide range of imaging and other equipment. We reason that cells, related reagents, and the technical skills of the research staff, not the devices themselves, are the most critical determinants of success. Extrapolation from concentration-response effects in microphysiological systems to human blood or oral exposures, difficulties with replicating the whole organ, and long-term functionality remain as critical challenges. Overall, we conclude that it is unlikely that a rodent- or human-equivalent model is achievable through a finite number of microphysiological systems in the near future; therefore, building consensus and promoting the gradual incorporation of these models into tiered approaches for safety assessment and decision-making is the sensible path to wide adoption.

Chemical and biological assessments of environmental mixtures: A review of current trends, advances, and future perspectives

Considering the chemical complexity and toxicity data gaps of environmental mixtures, most studies evaluate the chemical risk individually. However, humans are usually exposed to a cocktail of chemicals in real life. Mixture health assessment remains to be a research area having significant knowledge gaps. Characterization of chemical composition and bioactivity/toxicity are the two critical aspects of mixture health assessments. This review seeks to introduce the recent progress and tools for the chemical and biological characterization of environmental mixtures. The state-of-the-art techniques include the sampling, extraction, rapid detection methods, and the in vitro, in vivo, and in silico approaches to generate the toxicity data of an environmental mixture. Application of these novel methods, or new approach methodologies (NAMs), has increased the throughput of generating chemical and toxicity data for mixtures and thus refined the mixture health assessment. Combined with computational methods, the chemical and biological information would shed light on identifying the bioactive/toxic components in an environmental mixture.

Breakthroughs and Applications of Organ-on-a-Chip Technology

Organ-on-a-chip (OOAC) is an emerging technology based on microfluid platforms and in vitro cell culture that has a promising future in the healthcare industry. The numerous advantages of OOAC over conventional systems make it highly popular. The chip is an innovative combination of novel technologies, including lab-on-a-chip, microfluidics, biomaterials, and tissue engineering. This paper begins by analyzing the need for the development of OOAC followed by a brief introduction to the technology. Later sections discuss and review the various types of OOACs and the fabrication materials used. The implementation of artificial intelligence in the system makes it more advanced, thereby helping to provide a more accurate diagnosis as well as convenient data management. We introduce selected OOAC projects, including applications to organ/disease modelling, pharmacology, personalized medicine, and dentistry. Finally, we point out certain challenges that need to be surmounted in order to further develop and upgrade the current systems.

Emerging tissue engineering strategies for the corneal regeneration

Cornea as the outermost layer of the eye is at risk of various genetic and environmental diseases that can damage the cornea and impair vision. Corneal transplantation is among the most applicable surgical procedures for repairing the defected tissue. However, the scarcity of healthy tissue donations as well as transplantation failure has remained as the biggest challenges in confront of corneal grafting. Therefore, alternative approaches based on stem-cell transplantation and classic regenerative medicine have been developed for corneal regeneration. In this review, the application and limitation of the recently-used advanced approaches for regeneration of cornea are discussed. Additionally, other emerging powerful techniques such as 5D printing as a new branch of scaffold-based technologies for construction of tissues other than the cornea are highlighted and suggested as alternatives for corneal reconstruction. The introduced novel techniques may have great potential for clinical applications in corneal repair including disease modeling, 3D pattern scheming, and personalized medicine.

Organotypic and Microphysiological Human Tissue Models for Drug Discovery and Development-Current State-of-the-Art and Future Perspectives

The number of successful drug development projects has been stagnant for decades despite major breakthroughs in chemistry, molecular biology, and genetics. Unreliable target identification and poor translatability of preclinical models have been identified as major causes of failure. To improve predictions of clinical efficacy and safety, interest has shifted to three-dimensional culture methods in which human cells can retain many physiologically and functionally relevant phenotypes for extended periods of time. Here, we review the state of the art of available organotypic culture techniques and critically review emerging models of human tissues with key importance for pharmacokinetics, pharmacodynamics, and toxicity. In addition, developments in bioprinting and microfluidic multiorgan cultures to emulate systemic drug disposition are summarized. We close by highlighting important trends regarding the fabrication of organotypic culture platforms and the choice of platform material to limit drug absorption and polymer leaching while supporting the phenotypic maintenance of cultured cells and allowing for scalable device fabrication. We conclude that organotypic and microphysiological human tissue models constitute promising systems to promote drug discovery and development by facilitating drug target identification and improving the preclinical evaluation of drug toxicity and pharmacokinetics. There is, however, a critical need for further validation, benchmarking, and consolidation efforts ideally conducted in intersectoral multicenter settings to accelerate acceptance of these novel models as reliable tools for translational pharmacology and toxicology. SIGNIFICANCE STATEMENT: Organotypic and microphysiological culture of human cells has emerged as a promising tool for preclinical drug discovery and development that might be able to narrow the translation gap. This review discusses recent technological and methodological advancements and the use of these systems for hit discovery and the evaluation of toxicity, clearance, and absorption of lead compounds.

Microphysiological Systems: Stakeholder Challenges to Adoption in Drug Development

Microphysiological systems (MPS) or tissue chips/organs-on-chips are novel in vitro models that emulate human physiology at the most basic functional level. In this review, we discuss various hurdles to widespread adoption of MPS technology focusing on issues from multiple stakeholder sectors, e.g., academic MPS developers, commercial suppliers of platforms, the pharmaceutical and biotechnology industries, and regulatory organizations. Broad adoption of MPS technology has thus far been limited by a gap in translation between platform developers, end-users, regulatory agencies, and the pharmaceutical industry. In this brief review, we offer a perspective on the existing barriers and how end-users may help surmount these obstacles to achieve broader adoption of MPS technology.

Co-delivery of gemcitabine and cisplatin via Poly (L-glutamic acid)-g-methoxy poly (ethylene glycol) micelle to improve the in vivo stability and antitumor effect

PURPOSE

The intention of the study was to co-delivery gemcitabine and cisplatin with totally different nature by prodrug and micelle strategy to improve its in vivo stability and antitumor effect.

METHODS

A prodrug of gemcitabine (mPEG-PLG-GEM) was synthesized through the covalent conjugation between the primary amino group of gemcitabine and the carboxylic group of poly (L-glutamic acid)-g-methoxy poly (ethylene glycol) (mPEG-PLG). It was prepared into micelles by a solvent diffusion method, and then combined with cisplatin through chelation to prepare gemcitabine and cisplatin co-loaded mPEG-PLG micelles (mPEG-PLG-GEM@CDDP micelles).

RESULTS

Gemcitabine and cisplatin in each micelle group were released more slowly than in solutions. In addition, pharmacokinetics behaviors of them were improved after encapsulated in prodrug micelles. T_1/2z of gemcitabine and cisplatin encapsulated in micelles were prolonged to 6.357 h (mPEG-PLG-GEM), 10.490 h (mPEG-PLG@CDDP), 5.463 h and 12.540 h (mPEG-PLG-GEM@CDDP) compared with GEM@CDDP solutions (T_1/2z = 1.445 h and 7.740 h). The ratio of synergy between gemcitabine and cisplatin (3:1 ~ 1:1(n/n)) was guaranteed in the systemic circulation, thus improving its antitumor effect. The results of biochemical analysis showed that GEM@CDDP-Sol was more toxic to kidneys and marrow compared with mPEG-PLG-GEM@CDDP micelles.

CONCLUSIONS

By prodrug strategy, gemcitabine and cisplatin with totally different nature were prepared into micelles and obtained a better pharmacokinetic behavior. And the dual drug delivery system performed a better in vivo stability and antitumor effect compared with each single drug delivery system in the experiment. Scheme. Schematic of mPEG-PLG-GEM@CDDP micelles' formation and action process.

Modelling Renal Filtration and Reabsorption Processes in a Human Glomerulus and Proximal Tubule Microphysiological System

Kidney microphysiological systems (MPS) serve as potentially valuable preclinical instruments in probing mechanisms of renal clearance and osmoregulation. Current kidney MPS models target regions of the nephron, such as the glomerulus and proximal tubule (PCT), but fail to incorporate multiple filtration and absorption interfaces. Here, we describe a novel, partially open glomerulus and PCT microdevice that integrates filtration and absorption in a single MPS. The system equalizes pressure on each side of the PCT that operates with one side "closed" by recirculating into the bloodstream, and the other "opened" by exiting as primary filtrate. This design precisely controls the internal fluid dynamics and prevents loss of all fluid to the open side. Through this feature, an in vitro human glomerulus and proximal tubule MPS was constructed to filter human serum albumin and reabsorb glucose for seven days of operation. For proof-of-concept experiments, three human-derived cell types-conditionally immortalized human podocytes (CIHP-1), human umbilical vein endothelial cells (HUVECs), and human proximal tubule cells (HK-2)-were adapted into a common serum-free medium prior to being seeded into the three-component MPS (T-junction splitter, glomerular housing unit, and parallel proximal tubule barrier model). This system was optimized geometrically (tubing length, tubing internal diameter, and inlet flow rate) using in silico computational modeling. The prototype tri-culture MPS successfully filtered blood serum protein and generated albumin filtration in a physiologically realistic manner, while the device cultured only with proximal tubule cells did not. This glomerulus and proximal convoluted tubule MPS is a potential prototype for the human kidney used in both human-relevant testing and examining pharmacokinetic interactions.

Environmental Toxicology Assays Using Organ-on-Chip

Adverse effects of environmental toxicants to human health have traditionally been assayed using in vitro assays. Organ-on-chip (OOC) is a new platform that can bridge the gaps between in vitro assays (or 3D cell culture) and animal tests. Microenvironments, physical and biochemical stimuli, and adequate sensing and biosensing systems can be integrated into OOC devices to better recapitulate the in vivo tissue and organ behavior and metabolism. While OOCs have extensively been studied for drug toxicity screening, their implementation in environmental toxicology assays is minimal and has limitations. In this review, recent attempts of environmental toxicology assays using OOCs, including multiple-organs-on-chip, are summarized and compared with OOC-based drug toxicity screening. Requirements for further improvements are identified and potential solutions are suggested.

Kidney Organoid and Microphysiological Kidney Chip Models to Accelerate Drug Development and Reduce Animal Testing

Kidneys are critical for the elimination of many drugs and metabolites via the urine, filtering waste and maintaining proper fluid and electrolyte balance. Emerging technologies incorporating engineered three-dimensional (3D) in vitro cell culture models, such as organoids and microphysiological systems (MPS) culture platforms, have been developed to replicate nephron function, leading to enhanced efficacy, safety, and toxicity evaluation of new drugs and environmental exposures. Organoids are tiny, self-organized three-dimensional tissue cultures derived from stem cells that can include dozens of cell types to replicate the complexity of an organ. In contrast, MPS are highly controlled fluidic culture systems consisting of isolated cell type(s) that can be used to deconvolute mechanism and pathophysiology. Both systems, having their own unique benefits and disadvantages, have exciting applications in the field of kidney disease modeling and therapeutic discovery and toxicology. In this review, we discuss current uses of both hPSC-derived organoids and MPS as pre-clinical models for studying kidney diseases and drug induced nephrotoxicity. Examples such as the use of organoids to model autosomal dominant polycystic kidney disease, and the use of MPS to predict renal clearance and nephrotoxic concentrations of novel drugs are briefly discussed. Taken together, these novel platforms allow investigators to elaborate critical scientific questions. While much work needs to be done, utility of these 3D cell culture technologies has an optimistic outlook and the potential to accelerate drug development while reducing the use of animal testing.

Comprehensive Development in Organ-On-A-Chip Technology

The expeditious advancement in the organ on chip technology provided a phase change to the conventional in vitro tests used to evaluate absorption, distribution, metabolism, excretion (ADME) studies and toxicity assessments. The demand for an accurate predictive model for assessing toxicity and reducing the potential risk factors became the prime area of any drug delivery process. Researchers around the globe are welcoming the incorporation of organ-on-a-chips for ADME and toxicity evaluation. Organ-on-a-chip (OOC) is an interdisciplinary technology that evolved as a contemporary in vitro model for the pharmacokinetics and pharmacodynamics (PK-PD) studies of a proposed drug candidate in the pre-clinical phases of drug development. The OOC provides a platform that mimics the physiological functions occurring in the human body. The precise flow control systems and the rapid sample processing makes OOC more advanced than the conventional two-dimensional (2D) culture systems. The integration of various organs as in the multi organs-on-a-chip provides more significant ideas about the time and dose dependant effects occurring in the body when a new drug molecule is administered as part of the pre-clinical times. This review outlines the comprehensive development in the organ-on-a-chip technology, various OOC models and its drug development applications, toxicity evaluation and efficacy studies.

Microphysiological systems: What it takes for community adoption

Microphysiological systems (MPS) are promising in vitro tools which could substantially improve the drug development process, particularly for underserved patient populations such as those with rare diseases, neural disorders, and diseases impacting pediatric populations. Currently, one of the major goals of the National Institutes of Health MPS program, led by the National Center for Advancing Translational Sciences (NCATS), is to demonstrate the utility of this emerging technology and help support the path to community adoption. However, community adoption of MPS technology has been hindered by a variety of factors including biological and technological challenges in device creation, issues with validation and standardization of MPS technology, and potential complications related to commercialization. In this brief Minireview, we offer an NCATS perspective on what current barriers exist to MPS adoption and provide an outlook on the future path to adoption of these in vitro tools.

Environmental toxicology wars: Organ-on-a-chip for assessing the toxicity of environmental pollutants

Environmental pollution is a widespread problem, which has seriously threatened human health and led to an increase of human diseases. Therefore, it is critical to evaluate environmental pollutants quickly and efficiently. Because of obvious inter-species differences between animals and humans, and lack of physiologically-relevant microenvironment, animal models and in vitro two-dimensional (2D) models can not accurately describe toxicological effects and predicting actual in vivo responses. To make up the limitations of conventional environmental toxicology screening, organ-on-a-chip (OOC) systems are increasingly developing. OOC systems can provide a well-organized architecture with comparable to the complex microenvironment in vivo and generate realistic responses to environmental pollutants. The feasibility, adjustability and reliability of OCC systems make it possible to offer new opportunities for environmental pollutants screening, which can study their metabolism, collective response, and fate in vivo. Further progress can address the challenges to make OCC systems better investigate and evaluate environmental pollutants with high predictive power.

Beyond Polydimethylsiloxane: Alternative Materials for Fabrication of Organ-on-a-Chip Devices and Microphysiological Systems

Polydimethylsiloxane (PDMS) is the predominant material used for organ-on-a-chip devices and microphysiological systems (MPSs) due to its ease-of-use, elasticity, optical transparency, and inexpensive microfabrication. However, the absorption of small hydrophobic molecules by PDMS and the limited capacity for high-throughput manufacturing of PDMS-laden devices severely limit the application of these systems in personalized medicine, drug discovery, in vitro pharmacokinetic/pharmacodynamic (PK/PD) modeling, and the investigation of cellular responses to drugs. Consequently, the relatively young field of organ-on-a-chip devices and MPSs is gradually beginning to make the transition to alternative, nonabsorptive materials for these crucial applications. This review examines some of the first steps that have been made in the development of organ-on-a-chip devices and MPSs composed of such alternative materials, including elastomers, hydrogels, thermoplastic polymers, and inorganic materials. It also provides an outlook on where PDMS-alternative devices are trending and the obstacles that must be overcome in the development of versatile devices based on alternative materials to PDMS.