Real-Time Monitoring of Oxygen-Consumption Rate in Mouse Liver Slices Incubated in Organ-on-a-Chip Devices

We developed an organ-on-a-chip (OOC) based on precision-cut liver slices to assess liver function in real-time, both in health and disease, in a controlled and noninvasive manner. We achieved this by integrating fiber-optic-based oxygen sensors before and after the microchamber in which a liver slice was incubated under flow, to measure oxygen concentrations in the medium in real time. We first demonstrated that the basal oxygen consumption rate (OCR) of liver slices is a reliable indicator of liver slice viability. By monitoring basal OCR (2.9-5.7 pmol O₂/min/μg protein) in incubation medium, we found that it correlated well to cellular adenosine triphosphate (ATP) content (3.0-7.9 pmol/μg protein) (<i>r</i> = 0.82, <i>p</i> < 0.0001). Second, we induced a diseased state in liver slices by targeting the mitochondria, as they play a critical role in liver function and disease. We exposed the liver slices to succinate in abundance (40 mM) for short periods (1 h) to rapidly boost mitochondrial OCR. Two successive treatments of succinate increased the OCR of liver slices by 1.5 pmol/min/μg each time. However, between treatments, the liver slice OCR did not return to its basal OCR, instead decreasing drastically by 60-70%, suggesting succinate toxicity. We confirmed this with ATP analysis (1.0 pmol/μg protein) and hematoxylin and eosin staining, which showed tissue necrosis and apoptosis. Our system could be an advantageous model for future studies assessing liver (patho)physiology in response to potentially toxic drugs or lifestyle-related liver diseases.