Functional expression of system x_c⁻is upregulated by asbestos but not crystalline silica in murine macrophages

Abstract

Context Inhalation of asbestos or silica is associated with chronic and progressive diseases, including fibrosis, cancer, and increased risk of systemic autoimmunity. Because there is a need for treatment options for these diseases, a better understanding of their mechanistic etiologies is essential. While oxidative stress in macrophages is an early consequence of these exposures, it may also serve as a signaling mechanism involved in downstream immune dysregulation. The system xc- exchange protein is induced by oxidative stress, and exchanges equimolor levels of extracellular cystine for intracellular glutamate. Cystine is subsequently reduced to cysteine, the rate-limiting precursor for glutathione synthesis. Objective As the primary transporter responsible for cystine/glutamate exchange on macrophages, system xc- was hypothesized to be inducible in response to asbestos and silica, and to increase viability through protection from oxidative stress. Results When challenged with amphibole asbestos, but not crystalline silica, RAW 264.7 macrophages increased expression of xCT and the rate of cystine/glutamate exchange in sodium-free conditions. This upregulation was prevented with N-acetylcysteine, implicating oxidative stress. Cystine protected the macrophages from asbestos-induced oxidative stress and cell death, supporting the hypothesis that imported cystine was used for synthesis of cellular antioxidants. System xc- inhibitors, glutamate and S-4-carboxyphenylglycine ((S)-4-CPG), significantly increased oxidative stress and cell death of asbestos-treated macrophages. Conclusion System xc- plays a critical role in survival of macrophages exposed to asbestos, but not silica. These data demonstrate a very early difference in the cellular response to these silicates that may have important downstream implications in the pathologic outcome of exposure.

Selective inhibitory effects of 50-nm gold nanoparticles on mouse macrophage and spleen cells

“…The reduced ROS by AuNP was unexpected since macrophages generally undergo oxidative stress during phagocytosis of a variety of particles (Valles et al, 2006; Blake et al, 2007; Scherbart et al, 2011; Pfau et al, 2012). However, this may be highly affected by particle size.…”

Cytotoxicity of fractured quartz on THP-1 human macrophages: role of the membranolytic activity of quartz and phagolysosome destabilization

“…Here, we investigated the impact of quartz particles on human macrophages, specifically analyzing whether quartz can induce alterations of the phagolysosome membrane. To this aim, we compared the effect on cell viability and impact at the lysosomal level of three surface-differentiated quartz specimens, namely: an ad-hoc synthesized quartz crystal in respirable size (Pastero et al 2016 ), exposing as-grown, unfractured, regular faces; a synthetic quartz mechanically fractured down to a size similar to the as-grown quartz; and a cytotoxic commercial quartz dust used in several toxicological works, as a positive control (Allison 1966 ; Castranova 2004 ; Lison et al 2009 ; Pfau et al 2012 ). Human red blood cells were used as a model of the cellular membrane (not capable of internalization) for assessing quartz membranolytic activity and for evidencing the effect of protein adsorption on the membranolytic activity of fractured quartz.…”

Cytotoxicity and Characterization of Particles Collected From an Indium–Tin Oxide Production Facility

“…Equal volumes of 1× phosphate-buffered saline (PBS) were used as control conditions for each experiment, and 1 mM potassium dichromate (Cr(VI)) was used as a positive control for experiments in which intracellular ROS were measured (Ye et al, 1999). Crystalline silica (Min-U-Sil 5 μm) was used as a control particle in the MTT and caspase activation assays as silica was shown to be cytotoxic in vitro (Allison et al, 1966;Pfau et al, 2012;Castranova, 2004;Lison et al, 2009). …”