Diesel exhaust particulate matter impairs Toll-like receptor signaling and host defense against staphylococcal cutaneous infection in mice.

Air pollution is an emerging cause of mortality, affecting nearly 5 million people each year. Exposure to diesel exhaust fine particulate matter (PM2.5) aggravates respiratory and skin conditions. However, its impact on the protective immunity of the skin remains poorly understood. This study aimed to investigate the underlying molecular mechanism for adverse effects of PM2.5 on the host protective immunity using in vitro cell and in vivo mouse model. Intracellular translocation of Toll-like receptor 9 (TLR9) and CpG-DNA internalization were assessed in dendritic cells without or with PM2.5 treatment using immunofluorescence staining. Cytokine and nitric oxide production were measured in dendritic cells and macrophages without or with PM2.5 treatment. NF-κB and MAPK signaling was determined using western blotting. Skin disease severity, bacterial loads, and cytokine production were assessed in cutaneous Staphylococcus aureus (S. aureus) infection mouse model. PM2.5 interfered with TLR9 activation by inhibiting both TLR9 trafficking to early endosomes and CpG-DNA internalization via clathrin-mediated endocytosis. In addition, exposure to PM2.5 inhibited various TLR-mediated nitric oxide and cytokine production as well as MAPK and NF-κB signaling. PM2.5 rendered mice more susceptible to staphylococcal skin infections. Our results suggest that exposure to PM impairs TLR signaling and dampens the host defense against staphylococcal skin infections. Our data provide a novel perspective into the impact of PM on protective immunity which is paramount to revealing air pollutant-mediated toxicity on the host immunity.

Pulmonary toxicity following acute coexposures to diesel particulate matter and α-quartz crystalline silica in the Sprague-Dawley rat.

The effects of acute pulmonary coexposures to silica and diesel particulate matter (DPM), which may occur in various mining operations, were investigated in vivo. Rats were exposed by intratracheal instillation (IT) to silica (50 or 233 µg), DPM (7.89 or 50 µg) or silica and DPM combined in phosphate-buffered saline (PBS) or to PBS alone (control). At one day, one week, one month, two months and three months postexposure bronchoalveolar lavage and histopathology were performed to assess lung injury, inflammation and immune response. While higher doses of silica caused inflammation and injury at all time points, DPM exposure alone did not. DPM (50 µg) combined with silica (233 µg) increased inflammation at one week and one-month postexposure and caused an increase in the incidence of fibrosis at one month compared with exposure to silica alone. To assess susceptibility to lung infection following coexposure, rats were exposed by IT to 233 µg silica, 50 µg DPM, a combination of the two or PBS control one week before intratracheal inoculation with 5 × 105 Listeria monocytogenes. At 1, 3, 5, 7 and 14 days following infection, pulmonary immune response and bacterial clearance from the lung were evaluated. Coexposure to DPM and silica did not alter bacterial clearance from the lung compared to control. Although DPM and silica coexposure did not alter pulmonary susceptibility to infection in this model, the study showed that noninflammatory doses of DPM had the capacity to increase silica-induced lung injury, inflammation and onset/incidence of fibrosis.

Interaction of diesel exhaust particulate matter with mucins in simulated saliva fluids: Bioaccessibility of heavy metals and potential health risks.

Air pollution is one of the major environmental risks threatening human health, diesel exhaust particulate matter (DEPM) is an important source of urban air pollution, and oral ingestion is the primary route of exposure to atmospheric particulate matter. This study examined the bioaccessibility of Cr, Fe, and Zn in DEPM within simulated saliva fluids through in vitro experiments, interactions between the particles and mucins, and the mechanisms underlying the oxidative damage they cause. The results indicated that the interaction between DEPM and mucins altered the dispersibility, surface charge, and wettability of the particles, leading to increased release of heavy metals. Protein adsorption experiments and characterizations revealed that the adsorption of mucin by the particles resulted in a complexation reaction between the metals in the DEPM and the mucins, accompanied by fluorescence quenching of the protein. In addition, free radical assays and correlation analyses revealed that environmentally persistent free radicals generated by DEPM induce the production of reactive oxygen species (O2·-, HOOH, and·OH), which damage the secondary structure of mucins and increase the risk of oral diseases. Our study is the first to reveal the interaction between DEPM and mucins in saliva, elucidating the mechanisms of DEPM-induced oxidative damage. This is significant for understanding the oral health risks posed by the ingestion of atmospheric particulate matter.

Inhalation of diesel exhaust particulate matter induces locomotor hyperactivity and its relationship with brain and gut metabolism.

Diesel exhaust particulate matter (DEPM) are important components of urban air pollution worldwide. Recent studies proved that airborne DEPM can enter the human brain, which was associated with brain and mental diseases. In this study, we investigated the effects of DEPM exposure on behavior, and explored potential mechanisms from the perspective of metabolism in specific brain regions and short chain fatty acids (SCFAs) in the gut using mice. The results showed that inhalation of DEPM induced locomotor hyperactivity and a tendency for memory decline in mice. Exposure to DEPM disrupted motor behavior generation related cerebellar Purkinje cells, induced widespread reduction of neurotransmitters in the frontal cortex, and downregulated expression of genes encoding Brain-derived neurotrophic factor (BDNF) and involved in the Brain-blood-barrier (BBB) in the hippocampus. Moreover, there was a DEPM dose-dependent increase in fecal SCFA levels. Correlation analysis showed that DEPM-induced locomotor hyperactivity was mainly associated with decreased neurotransmission in the frontal cortex and increased gut SCFAs, and those associations were discussed. This study provides new insights into the mechanisms underpinning behavioral changes caused by air pollution, and extends our knowledge on the toxicity and health effects of airborne pollutants.

Inhalation of diesel exhaust particulate matter accelerates weight gain via regulation of hypothalamic appetite-related genes and gut microbiota metabolism.

Mice exposed to diesel exhaust particulate matter (DEPM) exhibited accelerated weight gain. Several hypothalamic genes, hormones (serum Hypothalamic-Pituitary-Adrenal (HPA) axis hormones and gastrointestinal peptide tyrosine tyrosine (PYY)), metabolites (intrahepatic triglyceride (IHTG) and fecal short-chain fatty acids (SCFAs)), and gut microbiota structure, which may influence obesity and appetite regulation, were examined. The result suggested that DEPM-induced accelerated weight gain may be associated with increased expression of hypothalamic Gamma-aminobutyric acid (GABA) type B receptor, tight junction protein, and orexin receptors, in addition with decreased IHTG and repressed HPA axis. Moreover, changes in the structure of intestinal microbiota are also related to weight changes, especially for phylum Firmicutes, genus Lactobacillus, and the ratio of relative abundance of Firmicutes and Bacteroidetes (F/B). DEPM exposure also caused widespread increase in the levels of intestinal SCFAs, the concentrations of propionic acid and isobutyric acid were associated with weight gain rate and the abundance of some bacteria. Although DEPM exposure caused changes in expression of hypothalamic serotonin, NPY, and melanocortin receptors, they were not associated with weight changes. Furthermore, no significant difference in gastrointestinal PYY and expression of hypothalamic receptors for leptin, insulin, and glucagon-like peptide 1 receptors was observed between DEPM-exposed and control mice.

Analyzing the Impact of Diesel Exhaust Particles on Lung Fibrosis Using Dual PCR Array and Proteomics: YWHAZ Signaling.

Air pollutants are associated with exacerbations of asthma, chronic bronchitis, and airway inflammation. Diesel exhaust particles (DEPs) can induce and worsen lung diseases. However, there are insufficient data to guide polymerase chain reaction (PCR) array proteomics studies regarding the impacts of DEPs on respiratory diseases. This study was performed to identify genes and proteins expressed in normal human bronchial epithelial (NHBE) cells. MicroRNAs (miRNAs) and proteins expressed in NHBE cells exposed to DEPs at 1 µg/cm2 for 8 h and 24 h were identified using PCR array analysis and 2D PAGE/LC-MS/MS, respectively. YWHAZ gene expression was estimated using PCR, immunoblotting, and immunohistochemical analyses. Genes discovered through an overlap analysis were validated in DEP-exposed mice. Proteomics approaches showed that exposing NHBE cells to DEPs led to changes in 32 protein spots. A transcriptomics PCR array analysis showed that 6 of 84 miRNAs were downregulated in the DEP exposure groups compared to controls. The mRNA and protein expression levels of YWHAZ, ß-catenin, vimentin, and TGF-ß were increased in DEP-treated NHBE cells and DEP-exposed mice. Lung fibrosis was increased in mice exposed to DEPs. Our combined PCR array-omics analysis demonstrated that DEPs can induce airway inflammation and lead to lung fibrosis through changes in the expression levels of YWHAZ, ß-catenin, vimentin, and TGF-ß. These findings suggest that dual approaches can help to identify biomarkers and therapeutic targets involved in pollutant-related respiratory diseases.

Astaxanthin protected against the adverse effects induced by diesel exhaust particulate matter via improving membrane stability and anti-oxidative property.

Diesel exhaust particulate matter (DPM), which has been clarified as a Group I carcinogenic agent, is still challenging in its detoxification due to the complex composition and toxic mechanisms. Astaxanthin (AST) is a pleiotropic small biological molecule widely used in medical and healthcare with surprising effects and applications. The present study aimed to investigate the protective effects of AST on DPM-induced injury and the underlying mechanism. Our results indicated that AST significantly suppressed the generation of phosphorylated histone H2AX (γ-H2AX, marker of DNA damage) and inflammation caused by DPM both in vitro and in vivo. Mechanistically, AST prevented the endocytosis and intracellular accumulation of DPM via regulating the stability and fluidity of plasma membranes. Moreover, the oxidative stress elicited by DPM in cells could also be effectively inhibited by AST, together with protecting the structure and function of mitochondria. These investigations provided clear evidence that AST notably reduced DPM invasion and intracellular accumulation by modulating the membrane-endocytotic pathway, which eventually reduced intracellular oxidative stress caused by DPM. Our data might provide a novel clue for curing and treating the harmful effects of particulate matter.

Potential hazards associated with interactions between diesel exhaust particulate matter and pulmonary surfactant.

Long term exposure to diesel exhaust particulate matter (DEPM) can induce numerous adverse health effects to the respiratory system. Understanding the interaction between DEPM and pulmonary surfactant (PS) can be an essential step toward preliminary evaluation of the impact of DEPM on pulmonary health. Herein, DEPM was explored for its interaction with 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC), the major component of PS. The results indicated that the surface pressure-area (π-A) isotherms of DPPC monolayers shifted toward lower molecular areas and the compression modulus (CS-1) reduced in the presence of DEPM. Atomic force microscopy image showed that DEPM can disrupt the ultrastructure of DPPC monolayers along with the direction of lateral compression. In addition, DPPC can in turn condition the surface properties of DEPM, permitting its agglomeration in aqueous media, which was attributed to the adsorption of DEPM to DPPC. Furthermore, the particle-bound polycyclic aromatic hydrocarbons (PAHs) could be desorbed from DEPM by the solubilization of DPPC and it was positively correlated with the hydrophobicity of PAHs. These findings revealed the toxicity of DEPM-associated PAHs and the role of DPPC in facilitating the removal of the inhaled particles, which can provide a new insight into the potential hazards of airborne particles on lung health.

Probiotics Function as Immunomodulators in the Intestine in C57Bl/6 Male Mice Exposed to Inhaled Diesel Exhaust Particles on a High-Fat Diet.

Epidemiological studies reveal a correlation between air pollution exposure and gastrointestinal (GI) diseases, yet few studies have investigated the role of inhaled particulate matter on intestinal integrity in conjunction with a high-fat (HF) diet. Additionally, there is currently limited information on probiotics in mitigating air-pollutant responses in the intestines. Thus, we investigated the hypothesis that exposure to inhaled diesel exhaust particles (DEP) and a HF diet can alter intestinal integrity and inflammation, which can be attenuated with probiotics. 4-6-w-old male C57Bl/6 mice on a HF diet (45% kcal fat) were randomly assigned to be exposed via oropharyngeal aspiration to 35 µg of DEP suspended in 35 µL of 0.9% sterile saline or sterile saline (CON) only twice a week for 4 w. A subset of mice was treated with 0.3 g/day of Winclove Ecologic® barrier probiotics (PRO) in drinking water throughout the duration of the study. Our results show that DEP exposure ± probiotics resulted in increased goblet cells and mucin (MUC)-2 expression, as determined by AB/PAS staining. Immunofluorescent quantification and/or RT-qPCR showed that DEP exposure increases claudin-3, occludin, zona occludens (ZO)-1, matrix metalloproteinase (MMP)-9, and toll-like receptor (TLR)-4, and decreases tumor necrosis factor (TNF)-α and interleukin (IL)-10 expression compared to CON. DEP exposure + probiotics increases expression of claudin-3, occludin, ZO-1, TNF-α, and IL-10 and decreases MMP-9 and TLR-4 compared to CON + PRO in the small intestine. Collectively, these results show that DEP exposure alters intestinal integrity and inflammation in conjunction with a HF diet. Probiotics proved fundamental in understanding the role of the microbiome in protecting and altering inflammatory responses in the intestines following exposure to inhaled DEP.

Hepatoprotective Effects of Streptococcus thermophilus LM1012 in Mice Exposed to Air Pollutants.

In this study, we explored whether the use of Streptococcus thermophilus LM1012 (TL-LM1012) as a safe probiotic exerts hepatoprotective effects by suppressing oxidative stress and inflammation in vitro and alleviating aspartate aminotransferase (AST), alanine aminotransferase (ALT), and lactate dehydrogenase (LDH) production in vivo. In a series of safety tests, TL-LM1012 was found to have a negative response to hemolysis and biogenic amines, as well as susceptibility to antibiotics. TL-LM1012 protected cell viability and suppressed cytotoxicity by inhibiting oxidative stress and induced heme oxygenase-1 and superoxide dismutase activity in a dose-dependent manner in diesel exhaust particulate matter (DEPM)-treated HepG2 cells. Moreover, proinflammatory cytokines, including tumor necrosis factor-α, interleukin (IL)-6, and IL-1ß, were suppressed in DEPM-treated splenocytes. In DEPM-treated mice, oral administration of TL-LM1012 regulated AST, ALT, and LDH production in the serum after 14 days of treatment. These findings indicate that TL-LM1012, a safe probiotic, provides a potent preventive or therapeutic effect against liver disease caused by air pollution.

Responsiveness assessment of a 3D tetra-culture alveolar model exposed to diesel exhaust particulate matter.

The aim of the current study was to evaluate the responses of a 3D tetra-culture alveolar model cultivated at the air-liquid-interface (ALI) after apical exposure to diesel exhaust particulate matter (DEPM) based on the three-tiered oxidative stress concept. The alveolar model exposed to increasing doses of DEPM (1.75-5 µg/cm2) responded with increasing activity of the anti-oxidant defense mechanisms (Nrf2 translocation, increased gene expression for anti-oxidant proteins and increased HMOX-1 synthesis) (tier 1). Higher exposure generated a proinflammatory response (NF-kB translocation, increased gene expression of pro-inflammatory cytokines and adhesion molecules, and increased IL-6 and IL-8 synthesis) (tier 2) and, finally, the highest doses applied resulted in a decrease of cell viability due to necrosis (extra-cellular release of LDH) or apoptosis (increased expression of the pro-apoptotic genes CASP7 and FAS) (tier 3). Overall, the results of our study demonstrate that the 3D tetra-culture model when directly exposed to DEPM potently generates a realistic response according to the three-tiered oxidative stress concept. Further evaluation and benchmarking against currently used in vivo rodent models is needed to show its suitability, and to serve in the future as an alternative for in vivo studies in the hazard evaluation of inhalable irritants.

Mutagenicity of biodiesel or diesel exhaust particles and the effect of engine operating conditions.

BACKGROUND: Changing the fuel supply from petroleum based ultra-low sulfur diesel (ULSD) to biodiesel and its blends is considered by many to be a viable option for controlling exposures to particulate material (PM). This is critical in the mining industry where approximately 28,000 underground miners are potentially exposed to relatively high concentrations of diesel particulate matter (DPM). This study was conducted to investigate the mutagenic potential of diesel engine emissions (DEE) from neat (B100) and blended (B50) soy-based fatty acid methyl ester (FAME) biodiesel in comparison with ULSD PM using different engine operating conditions and exhaust aftertreatment configurations. METHODS: The DPM samples were collected for engine equipped with either a standard muffler or a combination of the muffler and diesel oxidation catalytic converter (DOC) that was operated at four different steady-state modes. Bacterial gene mutation activity of DPM was tested on the organic solvent extracts using the Ames Salmonella assay. RESULTS: The results indicate that mutagenic activity of DPM was strongly affected by fuels, engine operating conditions, and exhaust aftertreatment systems. The mutagenicity was increased with the fraction of biodiesel in the fuel. While the mutagenic activity was observed in B50 and B100 samples collected from both light-and heavy-load operating conditions, the ULSD samples were mutagenic only at light-load conditions. The presence of DOC in the exhaust system resulted in the decreased mutagenicity when engine was fueled with B100 and B50 and operated at light-load conditions. This was not the case when engine was fueled with ULSD. Heavy-load operating condition in the presence of DOC resulted in a decrease of mutagenicity only when engine was fueled with B50, but not B100 or ULSD. CONCLUSIONS: Therefore, the results indicate that DPM from neat or blended biodiesel has a higher mutagenic potency than that one of ULSD. Further research is needed to investigate the health effect of biodiesel as well as efficiency of DOC or other exhaust aftertreatment systems.