How Organ-Chip Technology is Redefining Human Physiology and Disease Modelling

Written by Catrin Bevan, PhD Student at Queen Mary University of London.

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What are organ-chips?

Traditional 2D cell culture models do not accurately recapitulate the native tissue environment, as factors such as cell heterogeneity and dimensionality are poorly matched. Animal models, although systemic, do not always predict human biology. This leads to a poor recapitulation of human physiology and disease mechanisms. As well as this, there are clear ethical concerns when using animal models. Organizations such as the NC3Rs have highlighted the importance of new approach methodologies (NAMs), such as in vitro models, to reduce and replace animal experimentation. As a result, there is a strong interest in developing new models that can better mimic such.

Organ-chips are systems that represent a convergence of microfluidics and tissue engineering to replicate specific organ function and interactions between different tissues, and allow for the precise control of an array of parameters. The complexity of the models varies, but they are generally composed of multiple channels separated by an interface for cell communication, allowing the co-culture of multiple cell types in 2D or 3D. This makes organ-chips a useful technology in the study of tissue interfaces, as they can be used to recreate interactions at the tissue-tissue level of organization.

Introducing a 3D niche environment into the channels gives greater control over the architecture of the mimetic system, such as the stiffness, organization, or matrix composition and attachment profile. This promotes more complex cell-cell and cell-matrix interactions, in turn maintaining cell morphology and gene/protein expression to be more in vivo like. Some models can also incorporate mechanical stimulation. The inclusion of such forces is beneficial in studying how cells sense and respond to mechanical cues, especially in highly mechanoresponsive tissues such as bone and muscle, and replicating physiological functions such as peristalsis in a gut model or breathing in a lung model.

Culture media can be introduced into the channels with incorporation under dynamic flow, inducing shear stress forces, mimicking vascular perfusion or interstitial flow. To further increase complexity, chips can be connected to develop multi-organ-chips or body-chips. Precise control over the flow also enables optimal supply of nutrients and oxygen, increasing the long-term viability of cells, and allowing the circulation of signaling molecules, drugs, or immune cells. On-chip cell activation or differentiation can be achieved through the addition of growth factors and cytokines, such as animal component-free HumanKine proteins, which provide high bioavailability and native human conformation and post-translational modifications.

In some models, this dynamic flow also allows the collection of media effluent at different timepoints. A range of analyses can therefore be carried out throughout the experimental timeline, such as cell secretome analysis and barrier permeability assessment. Cell lysates can also be extracted at the end of an experiment, or cells can be stained in situ. Proteintech offer a range of solutions that can be used to get the best outputs from your chip set up, such as immunoassays for detection of proteins, cytokines and growth factors, or antibodies and nanobodies for high-quality immunofluorescence staining or western blot analysis.

Many users will fabricate their own chips in-house. Manufacturing methods and design consideration are dependent on parameters required for the organ(s) of interest. Factors such as size, number of channels, materials, and incorporation of mechanical stimulation can all be tailored, thereby expanding the potential of these systems. There are also a range of commercially available chips available on the market. Some of the leading manufacturers include Emulate, Mimetas, and TissUse. Homemade chips allow for adaptability and freedom to design your chips to suit the exact model you are developing; however, commercial chips provide greater consistency and standardization across devices. Nonetheless, the range of microfluidic systems available to purchase means that researchers can often find a device that is best suited to their model, rather than a one-size-fits-all approach.

Applications of Organ-Chips in research

As well as basic research and disease modeling tools, organ-chips can also be used in a range of other applications, such as personalized medicine and ADME-Tox (absorption, distribution, metabolism, elimination, toxicology) studies. For personalized medicine applications, patient samples such as primary cells/tissues, blood samples, and stem cells can be cultured in a device specifically engineered to incorporate relevant environmental factors based on personal health information. This can be used to predict specific cellular responses, thereby allowing for experimental optimization of different disease prevention or treatment strategies specific to the patient that would otherwise be impossible. If implemented in a healthcare setting, these techniques have the potential to inform clinical decision-making and improve patient outcomes.

ADME-Tox studies are carried out to investigate the fate of compounds in the human body. One of the most frequently used devices is the liver chip. This is largely because of the liver’s major role in drug metabolism and excretion. This results in the liver being highly affected by drug and chemical toxicity, making it a key organ of interest in drug development and testing.

One of the first examples of such models comes from Lee et al, where a cell loading channel containing hepatocytes was surrounded by an endothelial-like barrier to allow transport of nutrients or drugs from a feeder channel perfused with culture media. This design maintained mass transport exchange like that of the liver acinus, and can be multiplexed to include multiple sinusoids in a single device, improving the throughput (figure 1A, (Lee et al., 2007)).

More complex devices, such as the commercially available Liver-Chip device from Emulate, contain multiple cell types and the inclusion of an extracellular matrix. The Emulate chip is a quad-culture chip with two channels, the first being an epithelial channel containing primary hepatocytes sandwiched between two layers of ECM, and the second being a vascular channel lined with a mixture of liver sinusoidal endothelial cells (LSECs), stellate cells, and Kupffer cells. Media is perfused through both channels. Under these conditions, cells maintain their in vivo-like morphologies and architecture, forming bile canicular networks (Figure 1B, (Jang et al., 2019)).

Organ-chips as a more predictive tool in the pharmaceutical industry

Specifically in the drug development industry, a lack of efficiency means that the process of approving new drugs is lengthy and highly expensive. Approximately 75% of R&D costs are spent on failed candidates that are initially deemed successful in early testing, but later down the line are found to be unsafe or inefficient during human clinical trials (Paul et al., 2010). Organ-chip technology provides a promising approach to reducing the reliance on animal models and increasing research and development productivity.

Although the complete replacement of animal models is a far-off goal, in the shorter term, incorporating such models into preclinical drug development and regulatory pipelines could drive better decision-making and enhance productivity, largely reducing costs and time spent during this process. A landmark paper from Ewart et al (2022) tested the Emulate Liver-Chip previously against spheroid models with 27 different drugs to assess their prediction of hepatotoxicity. Eight of these drugs were previously found to induce liver toxicity clinically, despite passing animal testing evaluations.

Overall, the liver-chips correctly predicted toxicity in 12/15 toxic drugs (80% sensitivity) and yielded no false positives in the nontoxic drugs (100% specificity). Comparatively, 3D spheroid models yielded a sensitivity of 42% and specificity of 67% (Ewart et al., 2022). Including organ-chips in the screening workflow could more effectively filter out ineffective and unsafe drug candidates, in turn refining animal experimentation (figure 2).

Conclusion

Organ chip models are becoming increasingly popular in both academic and industry research settings, as their adaptability and high physiological relevance make them a desirable tool for a wide variety of applications. Incorporating these tools into research pipelines could help to accelerate scientific discovery and lead to new avenues of inquiry. Their small size and scalability could enable high-throughput screenings of drugs and novel interventions for pathological conditions.

As well as lowering the cost and time burden associated with research, organ-chip models will help in the shift away from animal-based methods, reducing the ethical and efficacy concerns that surround the use of animal models in research. With the worldwide increase in complex multimodalities, organ-chip models will allow researchers to potentially model entire organ systems on the benchtop, aiding in the study of complicated pathologies, while providing a significantly more accurate model when compared to 2D cell culture methods.

References

Ewart, L., Apostolou, A., Briggs, S. A., Carman, C. V., Chaff, J. T., Heng, A. R., Jadalannagari, S., Janardhanan, J., Jang, K.-J., Joshipura, S. R., Kadam, M. M., Kanellias, M., Kujala, V. J., Kulkarni, G., Le, C. Y., Lucchesi, C., Manatakis, D. V., Maniar, K. K., Quinn, M. E., Ravan, J. S., Rizos, A. C., Sauld, J. F. K., Sliz, J. D., Tien-Street, W., Trinidad, D. R., Velez, J., Wendell, M., Irrechukwu, O., Mahalingaiah, P. K., Ingber, D. E., Scannell, J. W. & Levner, D. 2022. Performance assessment and economic analysis of a human Liver-Chip for predictive toxicology. Communications Medicine, 2, 154.

Jang, K.-J., Otieno, M. A., Ronxhi, J., Lim, H.-K., Ewart, L., Kodella, K. R., Petropolis, D. B., Kulkarni, G., Rubins, J. E., Conegliano, D., Nawroth, J., Simic, D., Lam, W., Singer, M., Barale, E., Singh, B., Sonee, M., Streeter, A. J., Manthey, C., Jones, B., Srivastava, A., Andersson, L. C., Williams, D., Park, H., Barrile, R., Sliz, J., Herland, A., Haney, S., Karalis, K., Ingber, D. E. & Hamilton, G. A. 2019. Reproducing human and cross-species drug toxicities using a Liver-Chip. Science Translational Medicine, 11, eaax5516.

Lee, P. J., Hung, P. J. & Lee, L. P. 2007. An artificial liver sinusoid with a microfluidic endothelial-like barrier for primary hepatocyte culture. Biotechnology and Bioengineering, 97, 1340-1346.

Paul, S. M., Mytelka, D. S., Dunwiddie, C. T., Persinger, C. C., Munos, B. H., Lindborg, S. R. & Schacht, A. L. 2010. How to improve R&D productivity: the pharmaceutical industry's grand challenge. Nature Reviews Drug Discovery, 9, 203-214.

Emulate. 2020. Development and characterization of the species-specific liver-chip. Available: https://emulatebio.com/wp-content/uploads/2021/06/Emulate_Technical_Note_Liver_Chip_Characterization.pdf