Glomerulus-on-a-Chip: Current Insights and Future Potential Towards Recapitulating Selectively Permeable Filtration Systems

Design and simulation of a microfluidics-based artificial glomerular ultrafiltration unit to reduce cell-induced fouling

BACKGROUND

The microfluidic-based Glomerulus-on-Chips (GoC) are mostly cell based, that is, 3D cell culture techniques are used to culture glomerular cells in order to mimic glomerular ultrafiltration. These chips require high maintenance to keep cell viability intact. There have been some approaches to build non-cell-based GoCs but many of these approaches have the drawback of membrane fouling. This article presents a structural design and simulation study of a dialysate free microfluidic channel for replicating the function of the human glomerular filtration barrier. The key advancement of the current work is addressing the fouling issue by combining a pre-filter to eliminate cellular components and performing filtration on the blood plasma.

METHODS

The Laminar Flow Mixture Model in COMSOL Multiphysics 5.6 has been utilized to simulate the behavior of blood flow in the microchannels. The geometrical effect of microchannels on the separation of the filtrate was investigated. The velocity at the inlet of the microchannel and pore size of the filtration membrane are varied to see the change in outflow and filtration fraction.

RESULTS

The efficiency of the device is calculated in terms of the filtration fraction (FF%) formed. Simulation results show that the filtrate obtained is ~20% of the plasma flow rate in the channel, which resembles the glomerular filtration fraction.

CONCLUSION

Given that it is not dependent on the functionality of grown cells, the proposed device is anticipated to have a longer lifespan due to its non-cell-based design. The device's cost can be reduced by avoiding cell cultivation inside of it. It can be integrated as a glomerular functional unit with other units of kidney model to build a fully developed artificial kidney.

The role of podocyte injury in the pathogenesis of Fabry disease nephropathy

Renal involvement is one of the most severe morbidities of Fabry disease (FD), a multisystemic lysosomal storage disease with an X-linked inheritance pattern. It results from pathogenic variants in the GLA gene (Xq22.2), which encodes the production of alpha-galactosidase A (α-Gal), responsible for glycosphingolipid metabolism. Insufficient activity of this lysosomal enzyme generates deposits of unprocessed intermediate substrates, especially globotriaosylceramide (Gb3) and derivatives, triggering cellular injury and subsequently, multiple organ dysfunction, including chronic nephropathy. Kidney injury in FD is classically attributed to Gb3 deposits in renal cells, with podocytes being the main target of the pathological process, in which structural and functional alterations are established early and severely. This configures a typical hereditary metabolic podocytopathy, whose clinical manifestations are proteinuria and progressive renal failure. Although late clinical outcomes and morphological changes are well established in this nephropathy, the molecular mechanisms that trigger and accelerate podocyte injury have not yet been fully elucidated. Podocytes are highly specialized and differentiated cells that cover the outer surface of glomerular capillaries, playing a crucial role in preserving the structure and function of the glomerular filtration barrier. They are frequent targets of injury in many nephropathies. Furthermore, dysfunction and depletion of glomerular podocytes are essential events implicated in the pathogenesis of chronic kidney disease progression. We will review the biology of podocytes and their crucial role in regulating the glomerular filtration barrier, analyzing the main pathogenic pathways involved in podocyte injury, especially related to FD nephropathy.

Characterizing Glomerular Barrier Dysfunction with Patient-Derived Serum in Glomerulus-on-a-Chip Models: Unveiling New Insights into Glomerulonephritis

Glomerulonephritis (GN) is characterized by podocyte injury or glomerular filtration dysfunction, which results in proteinuria and eventual loss of kidney function. Progress in studying the mechanism of GN, and developing an effective therapy, has been limited by the absence of suitable in vitro models that can closely recapitulate human physiological responses. We developed a microfluidic glomerulus-on-a-chip device that can recapitulate the physiological environment to construct a functional filtration barrier, with which we investigated biological changes in podocytes and dynamic alterations in the permeability of the glomerular filtration barrier (GFB) on a chip. We also evaluated the potential of GN-mimicking devices as a model for predicting responses to human GN. Glomerular endothelial cells and podocytes successfully formed intact monolayers on opposite sides of the membrane in our chip device. Permselectivity analysis confirmed that the chip was constituted by a functional GFB that could accurately perform differential clearance of albumin and dextran. Reduction in cell viability resulting from damage was observed in all serum-induced GN models. The expression of podocyte-specific marker WT1 was also decreased. Albumin permeability was increased in most models of serum-induced IgA nephropathy (IgAN) and membranous nephropathy (MN). However, sera from patients with minimal change disease (MCD) or lupus nephritis (LN) did not induce a loss of permeability. This glomerulus-on-a-chip system may provide a platform of glomerular cell culture for in vitro GFB in formation of a functional three-dimensional glomerular structure. Establishing a disease model of GN on a chip could accelerate our understanding of pathophysiological mechanisms of glomerulopathy.

The Current Status and Use of Microphysiological Systems by the Pharmaceutical Industry: The International Consortium for Innovation and Quality Microphysiological Systems Affiliate Survey and Commentary

Microphysiological systems (MPS) are comprised of one or multiple cell types of human or animal origins that mimic the biochemical/electrical/mechanical responses and blood-tissue barrier properties of the cells observed within a complex organ. The goal of incorporating these in vitro systems is to expedite and advance the drug discovery and development paradigm with improved predictive and translational capabilities. Considering the industry need for improved efficiency and the broad challenges of model qualification and acceptance, the International Consortium for Innovation and Quality (IQ) founded an IQ MPS working group in 2014 and Affiliate in 2018. This group connects thought leaders and end users, provides a forum for crosspharma collaboration, and engages with regulators to qualify translationally relevant MPS models. To understand how pharmaceutical companies are using MPS, the IQ MPS Affiliate conducted two surveys in 2019, survey 1, and 2021, survey 2, which differed slightly in the scope of definition of the complex in vitro models under question. The surveys captured demographics, resourcing, rank order for organs of interest, compound modalities tested, and MPS organ-specific questions, including nonclinical species needs and cell types. The major focus of this manuscript is on results from survey 2, where we specifically highlight the context of use for MPS within safety, pharmacology, or absorption, disposition, metabolism, and excretion and discuss considerations for including MPS data in regulatory submissions. In summary, these data provide valuable insights for developers, regulators, and pharma, offering a view into current industry practices and future considerations while highlighting key challenges impacting MPS adoption. SIGNIFICANCE STATEMENT: The application of microphysiological systems (MPS) represents a growing area of interest in the drug discovery and development framework. This study surveyed 20+ pharma companies to understand resourcing, current areas of application, and the key challenges and barriers to internal MPS adoption. These results will provide regulators, tech providers, and pharma industry leaders a starting point to assess the current state of MPS applications along with key learnings to effectively realize the potential of MPS as an emerging technology.

Organ-on-a-chip meets artificial intelligence in drug evaluation

Drug evaluation has always been an important area of research in the pharmaceutical industry. However, animal welfare protection and other shortcomings of traditional drug development models pose obstacles and challenges to drug evaluation. Organ-on-a-chip (OoC) technology, which simulates human organs on a chip of the physiological environment and functionality, and with high fidelity reproduction organ-level of physiology or pathophysiology, exhibits great promise for innovating the drug development pipeline. Meanwhile, the advancement in artificial intelligence (AI) provides more improvements for the design and data processing of OoCs. Here, we review the current progress that has been made to generate OoC platforms, and how human single and multi-OoCs have been used in applications, including drug testing, disease modeling, and personalized medicine. Moreover, we discuss issues facing the field, such as large data processing and reproducibility, and point to the integration of OoCs and AI in data analysis and automation, which is of great benefit in future drug evaluation. Finally, we look forward to the opportunities and challenges faced by the coupling of OoCs and AI. In summary, advancements in OoCs development, and future combinations with AI, will eventually break the current state of drug evaluation.

Enhanced podocyte differentiation and changing drug toxicity sensitivity through pressure-controlled mechanical filtration stress on a glomerulus-on-a-chip

Podocytes, localized in the glomerulus, are a prognostic factor of proteinuria in kidney disease and are exposed to distinct physiological stimuli from basal to apical filtration flow. Research studies on drug discovery and disease modeling for glomerulopathy have developed a glomerulus-on-a-chip and studied podocyte mechanobiology to realize alternative methods to animal experiments. However, the effect of filtration stimulus on podocytes has remained unclear. Herein, we report the successful development of a user-friendly filtration culture device and system that can precisely control the filtration flow using air pressure control by incorporating a commercially available culture insert. It allows mouse podocytes to be cultured under filtration conditions for three days with a guarantee of maintaining the integrity of the podocyte layer. Using our system, this study demonstrated that podocyte damage caused by hyperfiltration resulting from glomerular hypertension, a common pathophysiology of many glomerulopathies, was successfully recapitulated and that filtration stimulus promotes the maturation of podocytes in terms of their morphology and gene expression. Furthermore, we demonstrated that filtration stimulus induced different drug responsiveness in podocytes than those seen under static conditions, and that the difference in drug responsiveness was dependent on the pharmacological mechanism. Overall, this study has revealed differentiating and pharmacodynamic properties of filtration stimulus and brings new insights into the research field of podocyte mechanobiology towards the realization of glomerulus-on-a-chip.