In vitro toxicity evaluation in A549 cells of diesel particulate matter from two different particle sampling systems and several resuspension media.

In urban areas, inhalation of fine particles from combustion sources such as diesel engines causes adverse health effects. For toxicity testing, a substantial amount of particulate matter (PM) is needed. Conventional sampling involves collection of PM onto substrates by filtration or inertial impaction. A major drawback to those methodologies is that the extraction process can modify the collected particles and alter their chemical composition. Moreover, prior to toxicity testing, PM samples need to be resuspended, which can alter the PM sample even further. Lastly, the choice of the resuspension medium may also impact the detected toxicological responses. In this study, we compared the toxicity profile of PM obtained from two alternative sampling systems, using in vitro toxicity assays. One system makes use of condensational growth before collection in water in an impinger - BioSampler (CG-BioSampler), and the other, a Dekati® Gravimetric Impactor (DGI), is based on inertial impaction. In addition, various methods for resuspension of DGI collected PM were compared. Tested endpoints included cytotoxicity, formation of cellular reactive oxygen species, and genotoxicity. The alternative collection and suspension methods affected different toxicological endpoints. The water/dimethyl sulfoxide mixture and cell culture medium resuspended particles, along with the CG-BioSampler sample, produced the strongest responses. The water resuspended sample from the DGI appeared least toxic. CG-BioSampler collected PM caused a clear increased response in apoptotic cell death. We conclude that the CG-BioSampler PM sampler is a promising alternative to inertial impaction sampling.

The toxic potential of a fourth-generation E-cigarette on human lung cell lines and tissue explants.

The use of electronic cigarettes (E-cigs) is rapidly increasing. The latest generation of E-cigs is highly customizable, allowing for high heating coil temperatures. The aim of this study was to assess the toxic potential of a fourth-generation E-cig. Aerosols generated from E-liquid with (24 mg/mL) and without nicotine, using a fourth-generation E-cig, were chemically analysed and compared with cigarette smoke (K3R4F). Human lung epithelial cell lines and distal lung tissue explants were exposed to E-cig vapour extract (EVE) and cigarette smoke extract for 24 hours and assessed for viability, inflammation, oxidative stress and genotoxicity. E-cig aerosols contained measurable levels of volatile organic compounds, aldehydes and polycyclic aromatic hydrocarbons, in general, to a much lesser extent than cigarette smoke. Higher levels of certain carbonyls, e.g. formaldehyde, were detected in the E-cig aerosols. EVEs decreased cell viability of BEAS-2B cells, whereas little effect was seen in A549 cells and distal lung tissue. The nicotine-containing EVE caused a greater decrease in cell viability and significant increase in DNA damage than the nicotine-free EVE. Increased cytotoxicity, reactive oxygen species production and genotoxicity were seen with cells and tissue exposed to cigarette smoke extract compared with EVEs. Although E-cig aerosols were less toxic than cigarette smoke, it was not benign. Moreover, the EVE containing nicotine was more toxic than the nicotine-free EVE. More research is needed on the short- and long-term health effects of vaping and the usage of newly emerging E-cig devices to evaluate better the potential negative effects of E-cigs on human health.

Serine Protease Inhibitors Restrict Host Susceptibility to SARS-CoV-2 Infections.

The coronavirus disease 2019, COVID-19, is a complex disease with a wide range of symptoms from asymptomatic infections to severe acute respiratory syndrome with lethal outcome. Individual factors such as age, sex, and comorbidities increase the risk for severe infections, but other aspects, such as genetic variations, are also likely to affect the susceptibility to SARS-CoV-2 infection and disease severity. Here, we used a human 3D lung cell model based on primary cells derived from multiple donors to identity host factors that regulate SARS-CoV-2 infection. With a transcriptomics-based approach, we found that less susceptible donors show a higher expression level of serine protease inhibitors SERPINA1, SERPINE1, and SERPINE2, identifying variation in cellular serpin levels as restricting host factors for SARS-CoV-2 infection. We pinpoint their antiviral mechanism of action to inhibition of the cellular serine protease, TMPRSS2, thereby preventing cleavage of the viral spike protein and TMPRSS2-mediated entry into the target cells. By means of single-cell RNA sequencing, we further locate the expression of the individual serpins to basal, ciliated, club, and goblet cells. Our results add to the importance of genetic variations as determinants for SARS-CoV-2 susceptibility and suggest that genetic deficiencies of cellular serpins might represent risk factors for severe COVID-19. Our study further highlights TMPRSS2 as a promising target for antiviral intervention and opens the door for the usage of locally administered serpins as a treatment against COVID-19. IMPORTANCE Identification of host factors affecting individual SARS-CoV-2 susceptibility will provide a better understanding of the large variations in disease severity and will identify potential factors that can be used, or targeted, in antiviral drug development. With the use of an advanced lung cell model established from several human donors, we identified cellular protease inhibitors, serpins, as host factors that restrict SARS-CoV-2 infection. The antiviral mechanism was found to be mediated by the inhibition of a serine protease, TMPRSS2, which results in a blockage of viral entry into target cells. Potential treatments with these serpins would not only reduce the overall viral burden in the patients, but also block the infection at an early time point, reducing the risk for the hyperactive immune response common in patients with severe COVID-19.

Acute Exposure to Diesel Exhaust Increases Muscle Sympathetic Nerve Activity in Humans.

Background Diesel exhaust (DE) emissions are a major contributor to ambient air pollution and are strongly associated with cardiovascular morbidity and mortality. Exposure to traffic-related particulate matter is linked with acute adverse cardiovascular events; however, the mechanisms are not fully understood. We examined the role of the autonomic nervous system during exposure to DE that has previously only been indirectly investigated. Methods and Results Using microneurography, we measured muscle sympathetic nerve activity (MSNA) directly in the peroneal nerve of 16 healthy individuals. MSNA, heart rate, and respiration were recorded while subjects rested breathing filtered air, filtered air with an exposure mask, and standardized diluted DE (300 µg/m3) through the exposure mask. Heart rate variability was assessed from an ECG. DE inhalation rapidly causes an increase in number of MSNA bursts as well as the size of bursts within 10 minutes, peaking by 30 minutes (P<0.001), compared with baseline filtered air with an exposure mask. No significant changes occurred in heart rate variability indices during DE exposure; however, MSNA frequency correlated negatively with total power (r2=0.294, P=0.03) and low frequency (r2=0.258, P=0.045). Heart rate correlated positively with MSNA frequency (r2=0.268, P=0.04) and the change in percentage of larger bursts (burst amplitude, height >50% of the maximum burst) from filtered air with an exposure mask (r2=0.368, P=0.013). Conclusions Our study provides direct evidence for the rapid modulation of the autonomic nervous system after exposure to DE, with an increase in MSNA. The quick increase in sympathetic outflow may explain the strong epidemiological data associating traffic-related particulate matter to acute adverse cardiovascular events such as myocardial infarction. Registration URL: https://www.clinicaltrials.gov; Unique identifier: NCT02892279.

Identification of vitamin C transporters in the human airways: a cross-sectional in vivo study.

OBJECTIVES: Vitamin C is an important low-molecular weight antioxidant at the air-lung interface. Despite its critical role as a sacrificial antioxidant, little is known about its transport into the respiratory tract lining fluid (RTLF), or the underlying airway epithelial cells. While several vitamin C transporters have been identified, such as sodium-ascorbate cotransporters (SVCT1/2) and glucose transporters (GLUTs), the latter transporting dehydroascorbate, knowledge of their protein distribution within the human lung is limited, in the case of GLUTs or unknown for SVCTs. SETTING AND PARTICIPANTS: Protein expression of vitamin C transporters (SVCT1/2 and GLUT1-4) was examined by immunohistochemistry in endobronchial biopsies, and by FACS in airway leucocytes from lavage fluid, obtained from 32 volunteers; 16 healthy and 16 mild asthmatic subjects. In addition, antioxidant concentrations were determined in RTLF. The study was performed at one Swedish centre. PRIMARY AND SECONDARY OUTCOME MEASURES: The primary outcome measure was to establish the location of vitamin C transporters in the human airways. As secondary outcome measures, RTLF vitamin C concentration was measured and related to transporter expression, as well as bronchial epithelial inflammatory and goblet cells numbers. RESULTS: Positive staining was identified for SVCT1 and 2 in the vascular endothelium. SVCT2 and GLUT2 were present in the apical bronchial epithelium, where SVCT2 staining was predominately localised to goblet cells and inversely related to RTLF vitamin C concentrations. CONCLUSIONS: This experimental study is the first to demonstrate protein expression of GLUT2 and SVCT2 in the human bronchial epithelium. A negative correlation between SVCT2-positive goblet cells and bronchial RTLF vitamin C concentrations suggests a possible role for goblet cells in regulating the extracellular vitamin C pool.