How Reversible Are the Effects of Fumed Silica on Macrophages? A Proteomics-Informed View

Abstract

Synthetic amorphous silica is one of the most used nanomaterials, and numerous toxicological studies have studied its effects. Most of these studies have used an acute exposure mode to investigate the effects immediately after exposure. However, this exposure modality does not allow the investigation of the persistence of the effects, which is a crucial aspect of silica toxicology, as exemplified by crystalline silica. In this paper, we extended the investigations by studying not only the responses immediately after exposure but also after a 72 h post-exposure recovery phase. We used a pyrolytic silica as the test nanomaterial, as this variant of synthetic amorphous silica has been shown to induce a more persistent inflammation in vivo than precipitated silica. To investigate macrophage responses to pyrolytic silica, we used a combination of proteomics and targeted experiments, which allowed us to show that most of the cellular functions that were altered immediately after exposure to pyrolytic silica at a subtoxic dose, such as energy metabolism and cell morphology, returned to normal at the end of the recovery period. However, some alterations, such as the inflammatory responses and some aldehyde detoxification proteins, were persistent. At the proteomic level, other alterations, such as proteins implicated in the endosomal/lysosomal pathway, were also persistent but resulted in normal function, thus suggesting cellular adaptation.

Immediate and sustained effects of cobalt and zinc-containing pigments on macrophages

“…However, a decrease could be noted after recovery for the cells exposed to PB28 at high concentration, probably linked to cobalt release. This scheme was not observed for interleukin 6, for which a sustained stimulation was observed for all particles, in line with what has been described previously for silica [33] or for silver nanowires [47].…”

“…This scheme was not observed for interleukin 6, for which a sustained stimulation was observed for all particles, in line with what has been described previously for silica [33] or for silver nanowires [47].…”

“…Coupled with the effects on phagocytosis, these results suggest that macrophages become slightly less efficient in fighting a bacterial infection when loaded with cobalt-containing pigments. Such an effect was not observed when macrophages were treated with amorphous silica [33], but was also observed when macrophages were treated with silver nanoparticles [32], which also release toxic metallic ions during the recovery phase. When compared to results obtained upon chronic exposure to silver nanoparticles [50], the results of this study on cobalt-containing pigments suggest that this decrease in performance may last over time, which is to be taken into account in the perspective of long-term effects of tattoos.…”

“…This may represent a mechanism underlying potential long-term adverse effects of tattoos using these inks, therefore justifying this work. To this purpose, we used an in vitro murine macrophage system in a load-recovery mode, in which the cells are first loaded over 24 hours with the particles and then let evolve without added particles for three days [32,33].…”

A Low-Serum Culture System for Prolonged in Vitro Toxicology Experiments on a Macrophage System

“…In the few papers that do address this question (Dalzon et al, 2019b;Torres et al, 2020a), or that study the effects of repeated exposures (Dalzon et al, 2020a;Torres et al, 2020b;Murugadoss et al, 2021) technical problems linked to cell proliferation were encountered. This discrepancy between the classical cell growth in culture and the negligible macrophage proliferation were addressed by working at high cell concentrations (confluency) in some cases (Dalzon et al, 2019b(Dalzon et al, , 2020aTorres et al, 2020aTorres et al, , 2020b and neglected in other studies (Murugadoss et al, 2021). There is thus a need for a system that would limit cell proliferation, while keeping cell viability and functionality for an extended period.…”