Assessing the in vitro toxicity of the lunar dust environment using respiratory cells exposed to Al(2)O(3) or SiO(2) fine dust particles

Influence of the spaceflight environment on macrophage lineages

Spaceflight and terrestrial spaceflight analogs can alter immune phenotypes. Macrophages are important immune cells that bridge the innate and adaptive immune systems and participate in immunoregulatory processes of homeostasis. Furthermore, macrophages are critically involved in initiating immunity, defending against injury and infection, and are also involved in immune resolution and wound healing. Heterogeneous populations of macrophage-type cells reside in many tissues and cause a variety of tissue-specific effects through direct or indirect interactions with other physiological systems, including the nervous and endocrine systems. It is vital to understand how macrophages respond to the unique environment of space to safeguard crew members with appropriate countermeasures for future missions in low Earth orbit and beyond. This review highlights current literature on macrophage responses to spaceflight and spaceflight analogs.

Cytotoxic effects of dental prosthesis grinding dust on RAW264.7 cells

Respiratory diseases, including pulmonary fibrosis, silicosis, and allergic pneumonia, can be caused by long-term exposure to dental prosthesis grinding dust. The extent of the toxicity and pathogenicity of exposure to PMMA dust, Vitallium dust, and dentin porcelain dust differs. The dust from grinding dental prosthesis made of these three materials was characterized in terms of morphology, particle size, and elemental composition. The adverse effects of different concentrations of grinding dust (50, 150, 300, 450, and 600 μg ml-l) on RAW264.7 macrophages were evaluated, including changes in cell morphology and the production of lactate dehydrogenase (LDH) and reactive oxygen species (ROS). The dust particles released by grinding dental prosthesis made of these materials had different morphologies, particle sizes, and elemental compositions. They also induced varying degrees of cytotoxicity in RAW264.7 macrophages. A possible cytotoxicity mechanism is the induction of lipid peroxidation and plasma membrane damage as the dust particles penetrate cells. Therefore, clinicians who regularly work with these materials should wear the appropriate personal protection equipment to minimize exposure and reduce the health risks caused by these particulates.

The effect of dust storm particles on single human lung cancer cells

Exposure to dust particles during dust storms can lead to respiratory problems, diseases, and even death. The effect of dust particles at the cellular level is poorly understood. In this study, we investigated the impact that dust storm particles (Montmorillonite) have on human lung epithelial cells (A549) at the single cell level. Using live-cell imaging, we continuously followed individual cells after exposure to a wide range of concentrations of dust particles. We monitored the growth trajectory of each cell including number and timing of divisions, interaction with the dust particles, as well as time and mechanism of cell death. We found that individual cells show different cellular fates (survival or death) even in response to the same dust concentration. Cells that died interacted with dust particles for longer times, and engulfed more dust particles, compared with surviving cells. While higher dust concentrations reduced viability in a dose-dependent manner, the effect on cell death was non-monotonic, with intermediate dust concentration leading to a larger fraction of dying cells compared to lower and higher concentrations. This non-monotonic relationship was explained by our findings that high dust concentrations inhibit cell proliferation. Using cellular morphological features, supported by immunoblots and proinflammatory cytokines, we determined that apoptosis is the dominant death mechanism at low dust concentrations, while higher dust concentrations activate necrosis. Similar single cell approaches can serve as a baseline for evaluating other aerosol types that will improve our understanding of the health-related consequences of exposure to dust storms.

Lunar soil simulants alter macrophage survival and function

Lunar regolith samples collected during previous Apollo missions were found to contain components that were established to be toxic to humans; however, the health effects due to inhalation of lunar soil as a whole are still unknown. Macrophages residing in the alveolar sacs of the lungs constitute one of the last lines of defense against inhaled particulates before entry into the bloodstream. Here, we examine the macrophage response to lunar simulants that are similar in chemical composition to the lunar regolith. We assess cytotoxicity, cellular morphology, phagocytosis of simulants and expression of inflammatory markers. Overall, the exposure of macrophages to lunar simulants results in moderate cytotoxicity and marked alteration of cell morphology and uptake of the simulants. Interestingly, simulant exposure decreased proinflammatory gene expression, but may induce an anti-inflammatory phenotype in the cells. These results illustrate that although macrophages phagocytose lunar simulants as a protective response, the simulants do induce a degree of macrophage cell death. Our study reveals some toxicity associated with lunar simulants and supports further evaluation of the inhalation of lunar regolith to understand the risks of exposure fully.

Effects of Astragalus and Codonopsis pilosula polysaccharides on alveolar macrophage phagocytosis and inflammation in chronic obstructive pulmonary disease mice exposed to PM2.5

Astragalus and Codonopsis pilosula are used for their immunomodulatory and anti-inflammatory effects. Here, we investigated the effects of Astragalus polysaccharides (APS) and Codonopsis pilosula polysaccharides (CPP) on alveolar macrophage (AM) phagocytosis and inflammation in chronic obstructive pulmonary disease (COPD) associated with exposure to particulate matter with a mean aerodynamic diameter ≤2.5μm (PM2.5). A mouse model of COPD was established by cigarette smoke exposure. PM2.5 exposure was performed by inhalation of a PM2.5 solution aerosol. APS and CPP were administered intragastrically. COPD showed defective AM phagocytosis and increased levels of interleukin (IL)-6, IL-8, and tumor necrosis factor (TNF)-α in bronchoalveolar lavage fluid and serum. PM2.5 exposure aggravated the damage, and this effect was reversed by APS and CPP gavage. The results indicate that APS and CPP may promote defective AM phagocytosis and ameliorate the inflammatory response in COPD with or without PM2.5 exposure.

Free-radical chemistry as a means to evaluate lunar dust health hazard in view of future missions to the moon

Lunar dust toxicity has to be evaluated in view of future manned missions to the Moon. Previous studies on lunar specimens and simulated dusts have revealed an oxidant activity assigned to HO· release. However, the mechanisms behind the reactivity of lunar dust are still quite unclear at the molecular level. In the present study, a complementary set of tests--including terephthalate (TA) hydroxylation, free radical release as measured by means of the spin-trapping/electron paramagnetic resonance (EPR) technique, and cell-free lipoperoxidation--is proposed to investigate the reactions induced by the fine fraction of a lunar dust analogue (JSC-1A-vf) in biologically relevant experimental environments. Our study proved that JSC-1A-vf is able to hydroxylate TA also in anaerobic conditions, which indicates that molecular oxygen is not involved in such a reaction. Spin-trapping/EPR measures showed that the HO· radical is not the reactive intermediate involved in the oxidative potential of JSC-1A-vf. A surface reactivity implying a redox cycle of phosphate-complexed iron via a Fe(IV) state is proposed. The role of this iron species was investigated by assessing the reactivity of JSC-1A-vf toward hydrogen peroxide (Fenton-like activity), formate ions (homolytic rupture of C-H bond), and linoleic acid (cell-free lipoperoxidation). JSC-1A-vf was active in all tests, confirming that redox centers of transition metal ions on the surface of the dust may be responsible for dust reactivity and that the TA assay may be a useful field probe to monitor the surface oxidative potential of lunar dust.