Better science with human cell-based organ and tissue models

An update on microfluidic multi-organ-on-a-chip systems for reproducing drug pharmacokinetics: the current state-of-the-art

INTRODUCTION

Advances in the accessibility of manufacturing technologies and iPSC-based modeling have accelerated the overall progress of organs-on-a-chip. Notably, the progress in multi-organ systems is not progressing with equal speed, indicating that there are still major technological barriers to overcome that may include biological relevance, technological usability as well as overall accessibility.

AREAS COVERED

We here review the progress in the field of multi-tissue- and body-on-a-chip pre and post- SARS-CoV-2 pandemic and review five selected studies with increasingly complex multi-organ chips aiming at pharmacological studies.

EXPERT OPINION

We discuss future and necessary advances in the field of multi-organ chips including how to overcome challenges regarding cell diversity, improved culture conditions, model translatability as well as sensor integrations to enable microsystems to cover organ-organ interactions in not only toxicokinetic but more importantly pharmacodynamic and -kinetic studies.

A benchtop brain injury model using resected donor tissue from patients with Chiari malformation

The use of live animal models for testing new therapies for brain and spinal cord repair is a controversial area. Live animal models have associated ethical issues and scientific concerns regarding the predictability of human responses. Alternative models that replicate the 3D architecture of the central nervous system have prompted the development of organotypic neural injury models. However, the lack of reliable means to access normal human neural tissue has driven reliance on pathological or post-mortem tissue which limits their biological utility. We have established a protocol to use donor cerebellar tonsillar tissue surgically resected from patients with Chiari malformation (cerebellar herniation towards the foramen magnum, with ectopic rather than diseased tissue) to develop an in vitro organotypic model of traumatic brain injury. Viable tissue was maintained for approximately 2 weeks with all the major neural cell types detected. Traumatic injuries could be introduced into the slices with some cardinal features of post-injury pathology evident. Biomaterial placement was also feasible within the in vitro lesions. Accordingly, this 'proof-of-concept' study demonstrates that the model offers potential as an alternative to the use of animal tissue for preclinical testing in neural tissue engineering. To our knowledge, this is the first demonstration that donor tissue from patients with Chiari malformation can be used to develop a benchtop model of traumatic brain injury. However, significant challenges in relation to the clinical availability of tissue were encountered, and we discuss logistical issues that must be considered for model scale-up.

The effect of ethanol and nicotine on ER stress in human placental villous explants

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Nicotine increased the GRP78/BiP protein in first trimester and term placental villous explants.

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Nicotine can cause endoplasmic reticulum stress in human placenta.

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Placental villous explants can be isolated from first trimester and term placenta to compare responses to toxic compounds.

Pregnant mothers continue smoking and drinking during pregnancy. To clarify the mechanisms of nicotine and ethanol toxicity during development, we have examined their effects on endoplasmic reticulum (ER) stress in human first trimester and term placental explants. First trimester and term human placental explants were treated with ethanol (2 ‰) or nicotine (15 µM), or their combination. The ER stress markers glucose regulated protein 78 (GRP78/BiP) and inositol requiring enzyme 1 α (IRE1α) were analyzed by immunoblotting. A statistically significant increase (p < 0.05) of GRP78/BiP by nicotine was noted in first trimester placental explants at 48 h, and in term placental explants at 24 h. Ethanol did not change protein expression of GRP78/BiP in either first trimester or term placental explants. IRE1α increased, although not statistically significantly, by all treatments in both first trimester and term placental explants. Thus, regardless of the known structural and functional differences in early and late placenta, both responded very similarly to the toxic compounds studied. These data support our earlier results in BeWo cells (Repo et al., 2014) implicating that nicotine induces ER stress in human placenta and may interfere with placental functions potentially disrupting fetal growth and development.

In Vitro Vascular Network Modified to Function as Culture Platform and Angiogenic Induction Potential Test for Cancer Cells

Drug treatments have been designed to inhibit tumor angiogenesis in hope of stopping tumor growth. However, not all tumor types respond to this type of treatment. A screening method which identifies angiogenesis inducing cancer types would help predict the efficacy of angiogenesis-inhibiting drugs for the patients. Our goal is to develop (1) a cell assay to assess the angiogenic induction potential of patient-derived tumor cells, and (2) a protocol for culturing cancer cells on a vascular platform. We optimized the media composition and seeding density of cells (hASC, HUVEC, and cancer cells) to 48-, 96-, and even 384-well plate sizes to allow vascular formation and cancer cell proliferation and subsequent analysis with high throughput. The angiogenic induction potential of patient-derived cancer cells was investigated by quantifying the formation of tubular structures and the drug response of cancer cells grown on a vascular platform was evaluated using gene expression and cell viability (WST-1) assay. Immunocytochemistry was performed with von Willebrand factor, collagen IV, CD44, cytokeratin 19 and ALDH1A1. The angiogenic induction potential test was shown to be responsive to the induction of angiogenesis by cancer cells. The responses of cancer cells were different when grown on a vascular platform or on plastic, seen in gene expression level and viability results. These two protocols are promising novel tools for aiding the selection of efficient cancer drugs for personalized medicine and as an alternative cancer cell culture platform.

Human BJ Fibroblasts is an Alternative to Mouse BALB/c 3T3 Cells in In Vitro Neutral Red Uptake Assay

The OECD GD 129 BALB/c 3T3 neutral red uptake (NRU) assay is a standardized test method for estimating starting dose for an acute oral systemic toxicity test in rodents. Mouse BALB/c 3T3 fibroblasts are the most commonly used cells in the NRU assay. We have previously transferred and validated BALB/c 3T3 NRU assay in our GLP laboratory. Subsequently, in order to obtain more human-relevant cytotoxicity data, we performed an intralaboratory validation using human BJ fibroblasts in the NRU assay instead of mouse BALB/c 3T3 fibroblasts. Here, we present comparative cytotoxicity data of 26 different test chemicals (pharmaceuticals, industrial chemicals, pesticides and food additives) produced with both BALB/c 3T3 NRU and BJ NRU assays.

Ionizing Radiation Alters Human Embryonic Stem Cell Properties and Differentiation Capacity by Diminishing the Expression of Activin Receptors

Exposure of the embryo to ionizing radiation (IR) is detrimental as it can cause genotoxic stress leading to immediate and latent consequences such as functional defects, malformations, or cancer. Human embryonic stem (hES) cells can mimic the preimplantation embryo and help to assess the biological effects of IR during early development. In this study, we describe the alterations H9 hES cells exhibit after X-ray irradiation in respect to cell cycle progression, apoptosis, genomic stability, stem cell signaling, and their capacity to differentiate into definitive endoderm. Early postirradiation, hES cells responded with an arrest in G2/M phase, elevated apoptosis, and increased chromosomal aberrations. Significant downregulation of stem cell signaling markers of the TGF beta-, Wnt-, and Hedgehog pathways was observed. Most prominent were alterations in the expression of activin receptors. However, hES cells responded differently depending on the culture conditions chosen for maintenance. Enzymatically passaged cells were less sensitive to IR than mechanically passaged ones showing fewer apoptotic cells and fewer changes in the stem cell signaling 24 h after irradiation, but displayed higher levels of chromosomal aberrations. Even though many of the observed changes were transient, surviving hES cells, which were differentiated 4 days postirradiation, showed a lower efficiency to form definitive endoderm than their mock-irradiated counterparts. This was demonstrated by lower expression levels of SOX17 and microRNA miR-375. In conclusion, hES cells are a suitable tool for the IR risk assessment during early human development. However, careful choice of the culture methods and a vigorous monitoring of the stem cell quality are mandatory for the use of these cells. Exposure to IR influences the stem cell properties of hES cells even when immediate radiation effects are overcome. This warrants consideration in the risk assessment of radiation effects during the earliest stages of human development.