A systematic review of kidney-on-a-chip-based models to study human renal (patho-)physiology

As kidney diseases affect ∼10% of the world population, understanding the underlying mechanisms and developing therapeutic interventions are of high importance. Although animal models have enhanced knowledge of disease mechanisms, human (patho-)physiology may not be adequately represented in animals. Developments in microfluidics and renal cell biology have enabled the development of dynamic models to study renal (patho-)physiology in vitro. Allowing inclusion of human cells and combining different organ models, such as kidney-on-a-chip (KoC) models, enable the refinement and reduction of animal experiments. We systematically reviewed the methodological quality, applicability and effectiveness of kidney-based (multi-)organ-on-a-chip models, and describe the state-of-the-art, strengths and limitations, and opportunities regarding basic research and implementation of these models. We conclude that KoC models have evolved to complex models capable of mimicking systemic (patho-)physiological processes. Commercial chips and human induced pluripotent stem cells and organoids are important for KoC models to study disease mechanisms and assess drug effects, even in a personalized manner. This contributes to the Reduction, Refinement and Replacement of animal models for kidney research. A lack of reporting of intra- and inter-laboratory reproducibility and translational capacity currently hampers implementation of these models.

The Past, Present and Future of Intestinal In Vitro Cell Systems for Drug Absorption Studies

The intestinal epithelium acts as a selective barrier for the absorption of water, nutrients and orally administered drugs. To evaluate the gastrointestinal permeability of a candidate molecule, scientists and drug developers have a multitude of cell culture models at their disposal. Static transwell cultures constitute the most extensively characterized intestinal in vitro system and can accurately categorize molecules into low, intermediate and high permeability compounds. However, they lack key aspects of intestinal physiology, including the cellular complexity of the intestinal epithelium, flow, mechanical strain, or interactions with intestinal mucus and microbes. To emulate these features, a variety of different culture paradigms, including microfluidic chips, organoids and intestinal slice cultures have been developed. Here, we provide an updated overview of intestinal in vitro cell culture systems and critically review their suitability for drug absorption studies. The available data show that these advanced culture models offer impressive possibilities for emulating intestinal complexity. However, there is a paucity of systematic absorption studies and benchmarking data and it remains unclear whether the increase in model complexity and costs translates into improved drug permeability predictions. In the absence of such data, conventional static transwell cultures remain the current gold-standard paradigm for drug absorption studies.