Nondestructive Optical Toxicity Assays of 3D Liver Spheroids with Optical Coherence Tomography

Abstract

given the central role of the liver in drug metabolism and detoxification, strong incentives exist to create new physiologically relevant, human-based, in vitro liver models which would offer better prediction of drug-induced liver injury in humans. Human hepatic HepaRG cells offer a spontaneous coculture model of hepatocytes and cholangiocytes, and maintain in vivo liver-specific functions, including phase I-III metabolism in 2D and 3D culture. [1] HepaRG cells are considered a sustainable surrogate to primary human hepatocytes [1] and a good cell model for pharmaceutical purposes, and therefore were the chosen cell type for this study.Despite many advances being made in the studies of 3D cellular models, there is still an unmet need for nondestructive quantitative assays. Many of the assays currently on the market were designed for 2D or suspension models, not for 3D culture models. Often, it is unknown if the reagents used in the assays can penetrate to the center of the 3D model, and for lytic assays, if it is possible for the reagent to disrupt every cell in the model. Another major issue that has come up with using these assays for 3D models is the optimization needed for each specific 3D model and each specific assay, regarding concentration of reagents, incubation time, and optimal cell number.Given established endpoint toxicity assays are often incompatible with assessing 3D dense tissues without destruction of the sample, we investigated the use of optical coherence tomography (OCT) as a novel approach to assess cellular activity nondestructively, and quantitatively, in response to acetaminophen (APAP) hepatotoxicity.OCT is an optical imaging modality that achieves micrometer resolution at millimeter depth. [2,3] Its main application is in the field of ophthalmology. [4] OCT enables fast label-free imaging of highly scattering tissues both in vitro and in vivo. Hence, it found applications in the nondestructive time-lapse imaging of in vitro engineered tissues throughout tissue development. [5,6] In this study, we investigated whether OCT together with speckle-variance techniques can be used to go beyond detecting live cells against inanimate biomaterials and can assess noninvasively, and in a dose-dependent manner, reduction in cellular activity associated with drug toxicity in 3D liver spheroids after exposure to a prototypical hepatotoxin, acetaminophen. (DILI) is the leading cause of failure in preclinical drug development and withdrawals. Given the central role of the liver in drug metabolism and detoxification, strong incentives exist to create new physiologically relevant, human-based, 3D in vitro liver models which will offer better prediction of DILI. However, most cell metabolic assays are designed for 2D culture and are not always suitable to assess 3D cultures; in addition, there is an emerging need to develop novel nondestructive assays to assess cell activity in a time-lapse fashion. In this study, optical coherence tomography (OCT) is used to measure the viability on 3D liver spheroids af...

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