Ultrastructural changes in the air–blood barrier in mice after intratracheal instillations of Asian sand dust and gold nanoparticles

Models to evaluate the pulmonary toxicity of desert dust and what we have learned from them so far: a mini-review

Millions of people worldwide are exposed to aerosolised desert dust and are at risk of the adverse respiratory health effects it causes. This mini-review gives an overview of the study types that can be used to assess the respiratory toxicity of desert dust and the insights gained from these studies. We highlight the main advantages and disadvantages of epidemiological, in vivo, and in vitro studies. Regarding in vitro studies, we discuss models of increasing complexity, i.e., traditional submerged cell cultures, air-liquid interface cultures, organ-on-a-chip models, organoids, and precision-cut lung slices. Epidemiological studies have shown increased short-term mortality and exacerbated acute and chronic respiratory diseases after desert dust events. In contrast, a connection to the onset of chronic diseases is more difficult to prove. In vivo and in vitro studies have particularly addressed the cellular and molecular effects of desert dust. It was found that desert dust activates immune cells and induces the expression of inflammatory cytokines and oxidative stress markers. The specific effects and their extent vary between dust samples from different sources. The investigation of the role of the composition is still immature and needs further effort including more extensive screenings. The advancement of easy-to-handle and realistic pulmonary in vitro models is required to automate screenings, support mechanistic insights, and enable the assessment of long-term exposure scenarios. In agreement with striving to develop new approach methodologies, such advancements can reduce and replace animal experiments and strongly benefit the translatability of research outcomes to human health protection.

The bio-distribution, clearance pathways, and toxicity mechanisms of ambient ultrafine particles

Ambient particles severely threaten human health worldwide. Compared to larger particles, ultrafine particles (UFPs) are highly concentrated in ambient environments, have a larger specific surface area, and are retained for a longer time in the lung. Recent studies have found that they can be transported into various extra-pulmonary organs by crossing the air-blood barrier (ABB). Therefore, to understand the adverse effects of UFPs, it is crucial to thoroughly investigate their bio-distribution and clearance pathways in vivo after inhalation, as well as their toxicological mechanisms. This review highlights emerging evidence on the bio-distribution of UFPs in pulmonary and extra-pulmonary organs. It explores how UFPs penetrate the ABB, the blood-brain barrier (BBB), and the placental barrier (PB) and subsequently undergo clearance by the liver, kidney, or intestine. In addition, the potential underlying toxicological mechanisms of UFPs are summarized, providing fundamental insights into how UFPs induce adverse health effects.

Mechanisms underlying the health effects of desert sand dust

Desertification and climate change indicate a future expansion of the global area of dry land and an increase in the risk of drought. Humans may therefore be at an ever-increasing risk of frequent exposure to, and resultant adverse health effects of desert sand dust. This review appraises a total of 52 experimental studies that have sought to identify mechanisms and intermediate endpoints underlying epidemiological evidence of an impact of desert dust on cardiovascular and respiratory health. Toxicological studies, in main using doses that reflect or at least approach real world exposures during a dust event, have demonstrated that virgin sand dust particles and dust storm particles sampled at remote locations away from the source induce inflammatory lung injury and aggravate allergen-induced nasal and pulmonary eosinophilia. Effects are orchestrated by cytokines, chemokines and antigen-specific immunoglobulin potentially via toll-like receptor/myeloid differentiation factor signaling pathways. Findings suggest that in addition to involvement of adhered chemical and biological pollutants, mineralogical components may also be implicated in the pathogenesis of human respiratory disorders during a dust event. Whilst comparisons with urban particulate matter less than 2.5 μm in diameter (PM2.5) suggest that allergic inflammatory responses are greater for microbial element-rich dust- PM2.5, aerosols generated during dust events appear to have a lower oxidative potential compared to combustion-generated PM2.5 sampled during non-dust periods. In vitro findings suggest that the significant amounts of suspended desert dust during storm periods may provide a platform to intermix with chemicals on its surfaces, thereby increasing the bioreactivity of PM2.5 during dust storm episodes, and that mineral dust surface reactions are an unrecognized source of toxic organic chemicals in the atmosphere, enhancing toxicity of aerosols in urban environments. In summary, the experimental research on desert dust on respiratory endpoints go some way in clarifying the mechanistic effects of atmospheric desert dust on the upper and lower human respiratory system. In doing so, they provide support for biological plausibility of epidemiological associations between this particulate air pollutant and events including exacerbation of asthma, hospitalization for respiratory infections and seasonal allergic rhinitis.

Acute exposure to C60 fullerene damages pulmonary mitochondrial function and mechanics

C60 fullerene (C60) nanoparticles, a nanomaterial widely used in technology, can offer risks to humans, overcome biological barriers, and deposit onto the lungs. However, data on its putative pulmonary burden are scanty. Recently, the C60 interaction with mitochondria has been described in vitro and in vivo. We hypothesized that C60 impairs lung mechanics and mitochondrial function. Thirty-five male BALB/c mice were randomly divided into two groups intratracheally instilled with vehicle (0.9% NaCl + 1% Tween 80, CTRL) or C60 (1.0 mg/kg, FUL). Twenty-four hours after exposure, 15 FUL and 8 CTRL mice were anesthetized, paralyzed, and mechanically ventilated for the determination of lung mechanics. After euthanasia, the lungs were removed en bloc at end-expiration for histological processing. Lung tissue elastance and viscance were augmented in FUL group. Increased inflammatory cell number, alveolar collapse, septal thickening, and pulmonary edema were detected. In other six FUL and six CTRL mice, mitochondria expressed reduction in state 1 respiration [FUL = 3.0 ± 1.14 vs. CTRL = 4.46 ± 0.9 (SEM) nmol O₂/min/mg protein, p = 0.0210], ATP production (FUL = 122.6 ± 18 vs. CTRL = 154.5 ± 14 μmol/100 μg protein, p = 0.0340), and higher oxygen consumption in state 4 [FUL = 12.56 ± 0.9 vs. CTRL = 8.26 ± 0.6], generation of reactive oxygen species (FUL 733.1 ± 169.32 vs. CTRL = 486.39 ± 73.1 nmol/100 μg protein, p = 0.0313) and reason ROS/ATP [FUL = 8.73 ± 2.3 vs. CTRL = 2.99 ± 0.3]. In conclusion, exposure to fullerene C60 impaired pulmonary mechanics and mitochondrial function, increased ROS concentration, and decrease ATP production.

Association of short term exposure to Asian dust with increased blood pressure

Air pollution causes hypertension, cardiovascular disease, and mortality. Asian dust (AD) reportedly induces asthma or acute myocardial infarction along with air pollution, but its impact on blood pressure (BP) is unknown. We investigated the association between short-term AD exposure and BP fluctuations in 300,952 individuals whose BP was measured during April 2005–March 2015 and divided them into AD and non-AD groups based on visitation for AD-related events. AD’s occurrence, air pollutants’ concentration (suspended particulate matter, SO₂, NO₂, photochemical oxidants), and meteorological variables (mean ambient temperature, relative humidity) were obtained from a monitoring station; AD events correlated with decreased visibility (< 10 km). We observed 61 AD days, with 3897 participants undergoing medical check-ups. Short-term AD exposure at lag day-0 was significantly associated with higher systolic BP (SBP), diastolic BP (DBP), and pulse rate (PR) risk (β = 1.85, 95% confidence interval (CI) 1.35–2.35 for SBP, β = 2.24, 95% CI 1.88–2.61 for DBP, β = 0.52, 95% CI 0.14–0.91 for PR) using multi-pollutant model. Population-attributable fractions exposed to AD were 11.5% for those with elevated SBP (SBP ≥ 120 mmHg) and 23.7% for those with hypertension (SBP ≥ 140 mmHg or DBP ≥ 90 mmHg). This study showed a strong association between short-term AD exposure and increased SBP and DBP.

Short-term exposure to desert dust and the risk of acute myocardial infarction in Japan: a time-stratified case-crossover study

Particulate matter from natural sources such as desert dust causes harmful effects for health. Asian dust (AD) increases the risk of acute myocardial infarction (AMI). However, little is known about the risk of myocardial infarction with nonobstructive coronary arteries (MINOCA), compared to myocardial infarction with coronary artery disease (MI-CAD). Using a time-stratified case-crossover design and conditional logistic regression models, the association between short-term exposure to AD whereby decreased visibility (< 10 km) observed at each monitoring station nearest to the hospitals was used for exposure measurements and admission for AMI in the spring was investigated using a nationwide administrative database between April 2012 and March 2016. According to presence of revascularization and coronary atherosclerosis, AMI patients (n = 30,435) were divided into 2 subtypes: MI-CAD (n = 27,202) or MINOCA (n = 3233). The single lag day-2 was used in AD exposure based on the lag effect analysis. The average level of meteorological variables and co-pollutants on the 3 days prior to the case/control days were used as covariates. The occurrence of AD events 2 days before the admission was associated with admission for MINOCA after adjustment for meteorological variables [odds ratio 1.65; 95% confidence interval (CI) 1.18-2.29], while the association was not observed in MI-CAD. The absolute risk difference of MINOCA admission was 1.79 (95% CI 1.21-2.38) per 100,000 person-year. These associations between AD exposure and the admission for MINOCA remained unchanged in two-pollutant models. This study provides evidence that short-term exposure to AD is associated with a higher risk of MINOCA, but not MI-CAD.

Ambient fine particulate matter induces inflammatory responses of vascular endothelial cells through activating TLR-mediated pathway

This study aims to investigate the role of Toll-like receptors (TLRs) on fine particulate matter (PM_2.5)-induced inflammatory responses of vascular endothelial cells. Inflammatory factors and TLRs were examined in the aorta of mice after nonsurgical intratracheal instillation of PM_2.5 as well as in the human umbilical vein endothelial cells (HUVECs) treated with PM_2.5. In addition, the effects of TLR2 and TLR4 inhibitors in the secretion of interleukin 6 (IL-6) and IL-1β and the expression of TLRs were determined in the HUVECs. The results showed that PM_2.5 could increase the expression of IL-1β, IL-6, TLR2, and TLR4 in vitro and in vivo. Anti-TLR2 IgG or TAK242, an inhibitor of TLR4, decreased the secretion of IL-1β and IL-6 by HUVECs and reduced the expression of corresponding TLRs. In conclusion, we demonstrate that both TLR2 and TLR4 are involved in PM_2.5-induced inflammatory responses of vascular endothelial cells. Inhibition of TLR2 and TLR4 expression has the potential to prevent PM_2.5-induced cardiovascular diseases.

Fluorescent reconstitution on deposition of PM2.5 in lung and extrapulmonary organs

The deposition of PM_2.5 (fine particulate matter in air with diameter smaller than 2.5 μm) in lungs is harmful to human health. However, real-time observation on the deposition of particles in the acinar area of the lung is still a challenge in experiments. Here, a fluorescent imaging method is developed to visualize the deposition process with a high temporal and spatial resolution. The observations reveal that the deposition pattern is nonuniform, and the maximum deposition rate in the acinar area differs significantly from the prediction of the widely used average deposition model. The method is also used to find single particles in the kidney and liver, though such particles are commonly believed to be too large to enter the extrapulmonary organs.

Inflammatory Changes in Lung Tissues Associated with Altered Inflammation-Related MicroRNA Expression after Intravenous Administration of Gold Nanoparticles in Vivo

Potential adverse effects of gold nanoparticles (AuNPs) are gaining attention due to their wide industrial, consumer, and biomedical applications. This may give rise to possible health risks from direct exposure to the NPs. Excessive inflammatory response is known to be one of the main effects induced by NPs. In this study, inflammatory and miRNA expression changes in lung tissues were evaluated in rats following intravenous administration of AuNPs. AuNPs (20 nm) at a mass concentration of 256 μg/mL were intravenously injected into 6-8 week old male Wistar rats at single doses of 0.025, 0.05, 0.1, and 0.2 mg/kg and sacrificed at 1 week, 1 month, and 2 months, respectively. The biodistribution of AuNPs in the lungs of the rats was determined by inductively coupled plasma mass spectrometry. There were no apparent changes observed in the body weight of the experimental rats. Histopathological examination revealed the presence of infiltrating lymphocytes in lung interstitial tissues and enhanced IL-1α immunostaining in the lung tissues. Out of 84 rat microRNAs (miRNAs) analyzed, the expression of three miRNAs in rat lungs were dysregulated by more than 2-fold in the 0.1 and 0.2 mg/kg AuNP-treated rats 1 week after exposure. In particular, miR-327 was significantly down-regulated in both groups of treated rats. Taken together, it would seem that miRNAs may regulate inflammatory changes in the lungs after exposure to AuNPs in vivo.

Tight junction between endothelial cells: the interaction between nanoparticles and blood vessels

Since nanoparticles are now widely applied as food additives, in cosmetics and other industries, especially in medical therapy and diagnosis, we ask here whether nanoparticles can cause several adverse effects to human health. In this review, based on research on nanotoxicity, we mainly discuss the negative influence of nanoparticles on blood vessels in several aspects and the potential mechanism for nanoparticles to penetrate endothelial layers of blood vessels, which are the sites of phosphorylation of tight junction proteins (claudins, occludins, and ZO (Zonula occludens)) proteins, oxidative stress and shear stress. We propose a connection between the presence of nanoparticles and the regulation of the tight junction, which might be the key approach for nanoparticles to penetrate endothelial layers and then have an impact on other tissues and organs.