Emulating the gut-liver axis: Dissecting the microbiome’s effect on drug metabolism using multi-organ-on-chip models
Over the past few years, several studies have shown that the gastrointestinal microbiome plays a key role in the processing of exogenous pharmaceutical compounds . Additionally, previous work on the gut-liver axis has shown that the interplay between the intestinal microbiome, the gut barrier and the liver is fundamental for regulating these drug metabolism processes . Disruption of these processes may lead to gut barrier dysfunction. This might result in the induction of inflammatory signaling pathways in the liver and ultimately modify drug metabolism by hepatocytes. Modeling the highly variable luminal gut environment and understanding how gut microbes can modulate drug availability or induce liver toxicity remains a challenge. Hence, there is a significant need to develop new platforms that enable the co-culture of human and microbial cells in a patient-specific manner. Microfluidics-based technologies such as organ-on-chips (OoC) could overcome current challenges in drug toxicity assessment assays as these technologies are designed to be more physiologically relevant than conventional in vitro and in vivo models. The main objective of this work is to interconnect our microfluidics-based Human Microbial Crosstalk (HuMiX) model  with the Dynamic42 liver-on-chip  in order to create a stem-cell based multi-organ platform to predict the effect of the gut microbiome on pharmacokinetics .
Theory and Experimental procedure
First, we aim to integrate transepithelial electrical resistance (TEER) electrodes into HuMiX and validate their functionality by evaluating the permeability of the intestinal epithelium in presence or absence of substances capable of inducing barrier disruption. Then, we plan to assess if the gut-liver platform mimics the tissues of interest and responds to pharmaceutical compounds of known action.
Figure 1: Schematic of HuMiX. HuMiX harbors four parallel channels, separated by semi-permeable membranes (red). HuMiX enables the co-culture of human cells (intestinal epithelial cells) and microbes (second and third layer, respectively). The presence of a nitrogen (N2) flow in the top channel establishes an anoxic environment for culturing anaerobic bacterial species from the gut. The environment within the device is routinely monitored through oxygen (O2) sensors. Integrated TEER sensors (golden), will ensure on-chip monitoring of the gut barrier integrity.
First experiments to interconnect HuMiX and the Dynamic42 liver-on-chip have been carried out using primary cells and immortalized cell lines. Experiments for evaluating cell viability and metabolic profiling in the established platforms are being performed by measuring the expression of tight junctions in intestinal cells and evaluating excretion of bile and albumin in hepatocytes. In addition, TEER electrodes have been successfully integrated into HuMiX (Figure 1) and preliminary experiments to validate their functionality have been performed.
The improvement of current OoC platforms could lead to a powerful alternative to stepwise replace the use of animal experimentation regarding the microbiome and its role on drug metabolization for individual patients.