Advanced In Vitro Testing Strategies and Models of the Intestine for Nanosafety Research

Abstract

There is growing concern about the potential adverse effects of oral exposure to engineered nanomaterials (ENM). Recent years have witnessed major developments in and advancement of intestinal in vitro models for nanosafety evaluation. The present paper reviews the key factors that should be considered for inclusion in nonanimal alternative testing approaches to reliably reflect the in vivo dynamics of the physicochemical properties of ENM as well the intestinal physiology and morphology. Currently available models range from simple cell line-based monocultures to advanced 3D systems and organoids. In addition, in vitro approaches exist to replicate the mucous barrier, digestive processes, luminal flow, peristalsis, and interactions of ENM with the intestinal microbiota. However, while the inclusion of a multitude of individual factors/components of particle (pre)­treatment, exposure approach, and cell model approximates in vivo-like conditions, such increasing complexity inevitably affects the system’s robustness and reproducibility. The selection of the individual modules to build the in vitro testing strategy should be driven and justified by the specific purpose of the study and, not least, the intended or actual application of the investigated ENM. Studies that address health hazards of ingested ENM likely require different approaches than research efforts to unravel the fundamental interactions or toxicity mechanisms of ENM in the intestine. Advanced reliable and robust in vitro models of the intestine, especially when combined in an integrated testing approach, offer great potential to further improve the field of nanosafety research.

Understanding the impact of more realistic low-dose, prolonged engineered nanomaterial exposure on genotoxicity using 3D models of the human liver

“…It is widely acknowledged that it is unsustainable and ethically divisive to rely primarily on in vivo based test systems for comprehensive ENM hazard assessment, as such, research into suitable, physiologically relevant in vitro alternatives has been at the forefront of nanotoxicology in recent years. Not only have scientists strived to alleviate the limitations of current in vitro models to enhance the longevity and predictivity of the models, but, as in the present study, there have been recent efforts to start addressing the manner in which humans are exposed to ENMs in natural life [ 38 , 39 ]. This study aimed to determine, firstly, if a more realistic, low-dose prolonged ENM exposure would provoke a significantly different (geno)toxicological effect compared to an acute exposure in 3D HepG2 spheroids.…”

Effects of dietary exposure to the engineered nanomaterials CeO2, SiO2, Ag, and TiO2 on the murine gut microbiome

“…In this context, determining the concentration of butyrate in the intestinal lumen or in the stool would be of particular interest. In concurrent in vitro investigations with advanced models of the human gut (Kampfer, Busch, and Schins 2020) we are exploring the effects of the presence of butyrate and varying butyrate concentrations in combination with ENM exposure.…”

“…Besides, indirect oral exposure to ENM may also arise from their release into the environment (Rico et al 2011;Keller et al 2013). Research into the effects of ingested ENM has long focused on systemic availability, addressed in toxicokinetic studies, as well as on potential toxic effects on the intestinal barrier, addressed in vivo and, increasingly, using advanced in vitro models (Kampfer, Busch, and Schins 2020). Only in recent years, awareness and interest have risen concerning possible perturbations of the gut microbiome induced by ENM (Bergin and Witzmann 2013;Pietroiusti, Magrini, and Campagnolo 2016).…”

Innovative in vitro strategies for food and environmental safety

“…Mucus has important defensive properties and strongly affects the mobility of nanoparticles, while M cells are involved in the absorption of nano-sized particulates (Beloqui et al, 2017). An advanced tri-culture model based on Caco-2 cells/HT29-MTX mucus secreting cells/lymphoblastoid Raji-B cells has been developed for qualitative/quantitative assessment of absorption and translocation of NMs (García-Rodríguez et al, 2018;Kämpfer et al, 2020). Conversion of Caco-2 cells into M-like cells, achieved by co-culturing Caco-2 with Raji B cells, has been assessed by electrophysiological, histological, biochemical and functional measurements.…”