Liver Microphysiological Systems for Predicting and Evaluating Drug Effects

Abstract

Liver plays a major role in drug metabolism and is one of the main sites of drug adverse effects. Microphysiological systems (MPS), also known as organs-on-a-chip, are a class of microfluidic platforms that recreate properties of tissue microenvironments. Among different properties, the liver microenvironment is three-dimensional, fluid flows around its cells, and different cell types regulate its function. Liver MPS aim to recreate these properties and enable drug testing and measurement of functional endpoints. Tests with these systems have demonstrated their potential for predicting clinical drug effects. Properties of liver MPS that improve the physiology of cell culture are reviewed, specifically focusing on the importance of recreating a physiological microenvironment to evaluate and model drug effects. Advances in modeling hepatic function by leveraging MPS are addressed, noting the need for standardization in the use, quality control, and interpretation of data from these systems.

Figure 1

Microphysiological systems (MPS) as advanced platforms to model cellular properties in vitro. Petri dishes and similar two‐dimensional (2‐D) cell culture platforms have been used for almost a century as test beds for maintaining cell cultures and modeling the translation of their biological properties to clinical observations. More recently, spheroid technology has enabled the possibility of simultaneously coculturing different cell types that represent tissue‐specific cellular varieties in three‐dimensions (3‐D) configuration to recreate more physiologically relevant settings in vitro. For developing MPS, organoid‐like coculture approaches were integrated in microfluidic devices with the intent of further improving the physiological relevance of 3‐D cocultures, with the potential to also address several limitations related to lack of human‐specific properties of preclinical tests used in drug development. The field is fast evolving to the deployment of interconnected systems representing interorgan communications and the modeling of more physiologically relevant in vitro assays (63). Illustrations are inspired by different sources.89, 90 [Colour figure can be viewed at wileyonlinelibrary.com]

Figure 2

Drug development with liver MPS. Liver microphysiological systems (MPS) result from coculturing different cell types in microfluidic settings that are designed to set the physiology of cellular function. (a) MPS can model drug effects via analysis of metabolism, drug–drug interactions, biomarkers, and phenotypes, such as transport, structure, metabolites, and toxicity. (b) The microenvironment of the liver lobule is multicellular, three‐dimensional, under flow, and defines the sinusoid. (c) two‐dimensional sandwich culture of hepatocytes between a collagen‐coated surface and a layer of Matrigel preserves hepatic function. (d–f) Different designs of liver MPS. Microtissues attach to scaffolds and are exposed to media flow and oxygen gradients in d. Microfluidic chambers (e and f) can also maintain tissue function, under oxygen gradients.91 A porous membrane can separate endothelial cells from hepatocytes to mimic a barrier (f). Illustrations are inspired by different sources.42, 43 [Colour figure can be viewed at wileyonlinelibrary.com]

Figure 3

Physiological zonation and cellular activity in the sinusoid unit of the liver. In a healthy and mature liver, oxygen (O₂) tension decreases as blood flows along the sinusoid unit (as detailed in Figure  2), from the portal triad (zone 1) to the central vein (zone 3). Different types of cell‐based molecular activities relate to this oxygen tension gradient. Glucose concentration, glycolytic activity, albumin and urea production, Wnt signaling and phosphorylation (phos.) of β‐catenin vary as noted in relation to oxygen concentration. The illustration is inspired by different sources.43, 50 Other cellular functions vary along the hepatic sinusoid, a topic reviewed elsewhere.49, 50, 51 [Colour figure can be viewed at wileyonlinelibrary.com]

Figure 4

Applications of liver microphysiological systems (MPS) in the field of clinical pharmacology. To understand clinical drug action, studies in clinical pharmacology aim to characterize drug pharmacokinetics, pharmacodynamics, and their relationship to drug effects. For this purpose, different assays can be developed or adapted to liver MPS, and these systems can be used simultaneously to measure, for example, therapeutic and toxic concentrations, characterize metabolism and transporter effects, and evaluate drug–drug interactions. The potential to multiplex different types of measurements in MPS can provide data to support pharmacology models to inform the clinical study design. Pharmacokinetic studies with MPS are also useful for understanding mechanisms that affect drug (and metabolite) concentrations in plasma and liver. [Colour figure can be viewed at wileyonlinelibrary.com]

Figure 5

Different possible modes of operation of liver microphysiological systems (MPS) based on circulation of cell culture medium. Developed systems can differ from each other on operational levels that relate to the way cell culture medium is supplied to the cell culture unit. These operational levels have a strong impact in the kinetics of cellular metabolism and energetics due to differences in cellular exposure to nutrients, metabolites, and drugs, which eventually affect system response to drugs.63 (a) Medium can be recirculated and completely changed every 2–3 days throughout the operation time.53 (b) Soluble medium components or compounds can be supplied between media changes.39 (c) Fresh medium can be continuously perfused into the cell culture unit.61 S represents drug substrates, M represents drug metabolites, and X represents carbon sources or other soluble components that set cellular function or physiology. 3‐D, three‐dimensional. [Colour figure can be viewed at wileyonlinelibrary.com]