# Nanoceria’s Silent Threat: Investigating Acute and Sub-Chronic Effects of CeO2 Nanopowder (≤50 nm) on the Human Intestinal Epithelial Cells

## TL;DR

This study explores how nanoceria (CeO2) affects human intestinal cells over short and long-term exposures, revealing potential health risks.

## Contribution

The novelty is the sub-chronic in vitro exposure assessment of CeO2 nanopowder on intestinal cells over 35 days.

## Key findings

- CeO2 NP caused dose- and time-dependent cytotoxicity and pro-oxidant effects up to 14 days.
- Mitochondrial impairment peaked at 7 days but showed recovery, while genotoxicity suggested DNA repair saturation.
- Sub-chronic exposure led to irreversible cell damage and reduced cell replication, with overexpression of mitophagy-related genes.

## Abstract

The increased mobilization of Rare Earth Elements (REEs), due to emerging technologies, could impact human health. The study assessed the effects of CeO2 nanopowder (100 μg/mL) in human intestinal cells (HT-29) following both acute (24 h) and, a novelty for in vitro study, sub-chronic exposure, treating subcultures of exposed cells to CeO2 NP up to 35 days. Recovery was also examined in exposed cells’ progeny. CeO2 NP internalization and acute cytotoxicity were dose and time dependent. A significant pro-oxidant effect was observed for up to 14 days. The highest mitochondrial impairment was detected after 7 days, but in post-exposure experiments the recovery was observed. Conversely, genotoxicity highlighted the saturation of the DNA repair mechanisms. The irreversible cell damage of sub-chronic exposure was highlighted by the percentage of death cells (p = 0.011) and by the weekly cell replication index (5.68 vs. 7.41). The homeostatic mitophagy pathway was able to counteract ROS-induced mitochondrial dysfunction, as shown by overexpression of ATG5, LC3, and BECN1 genes throughout the examined times. Instead, the overexpression of the pro-apoptotic gene Bax was very brief, highlighting that prolonged exposure might cause more widespread adverse effects, also involving cells that are not directly exposed to nanoceria.