Nitrogen dioxide (NO₂) is a pervasive gaseous air pollutant with well‐documented hazardous effects on health, necessitating precise toxicological characterization. While prior research has primarily focused on lower airway structures, the upper airways, serving as the first line of defense against airborne substances, remain understudied. This study aimed to investigate the functional effects of NO₂ exposure alone or in combination with hypoxia as a secondary stimulus on nasal epithelium and elucidate its molecular mechanisms because hypoxia is considered a pathophysiological factor in the onset and persistence of chronic rhinosinusitis, a disease of the upper airways. Air–liquid interface cell cultures derived from primary nasal mucosa cells were utilized as an in vitro model, offering a high in vitro–in vivo correlation. Our findings demonstrate that NO₂ exposure induces malfunction of the epithelial barrier, as evidenced by decreased transepithelial electrical resistance and increased fluorescein isothiocyanate (FITC)‐dextran permeability. mRNA expression analysis revealed a significant increase in IL‐6 and IL‐8 expressions following NO₂. Reduced mRNA expression of the tight junction component occludin was identified as a structural correlate of the damaged epithelial barrier. Notably, hypoxic conditions alone did not alter epithelial barrier integrity. These findings provide information on the harmful effects of NO₂ exposure on the human nasal epithelium, including compromised barrier integrity and induction of inflammatory responses. Overall, this study contributes to our understanding of pathophysiological mechanisms underlying also upper airway respiratory diseases associated with air pollution exposure and emphasizes the importance of mitigating NO₂ emissions to safeguard respiratory health.

Radioresistance is an important cause of head and neck cancer therapy failure. Zinc oxide nanoparticles (ZnO-NP) mediate tumor-selective toxic effects. The aim of this study was to evaluate the potential for radiosensitization of ZnO-NP. The dose-dependent cytotoxicity of ZnO-NP_{20 nm} and ZnO-NP_{100 nm} was investigated in FaDu and primary fibroblasts (FB) by an MTT assay. The clonogenic survival assay was used to evaluate the effects of ZnO-NP alone and in combination with irradiation on FB and FaDu. A formamidopyrimidine-DNA glycosylase (FPG)-modified single-cell microgel electrophoresis (comet) assay was applied to detect oxidative DNA damage in FB as a function of ZnO-NP and irradiation exposure. A significantly increased cytotoxicity after FaDu exposure to ZnO-NP_{20 nm} or ZnO-NP_{100 nm} was observed in a concentration of 10 µg/mL or 1 µg/mL respectively in 30 µg/mL of ZnO-NP_{20 nm} or 20 µg/mL of ZnO-NP_{100 nm} in FB. The addition of 1, 5, or 10 µg/mL ZnO-NP_{20 nm} or ZnO-NP_{100 nm} significantly reduced the clonogenic survival of FaDu after irradiation. The sub-cytotoxic dosage of ZnO-NP_{100 nm} increased the oxidative DNA damage compared to the irradiated control. This effect was not significant for ZnO-NP_{20 nm}. ZnO-NP showed radiosensitizing properties in the sub-cytotoxic dosage. At least for the ZnO-NP_{100 nm}, an increased level of oxidative stress is a possible mechanism of the radiosensitizing effect.

Zinc oxide nanoparticles (ZnO-NP) are commonly used for a variety of applications in everyday life. In addition, due to its versatility, nanotechnology supports promising approaches in the medical sector. NP can act as drug-carriers in the context of targeted chemo- or immunotherapy, and might also exhibit autonomous immune-modulatory characteristics. Knowledge of potential immunosuppressive or stimulating effects of NP is indispensable for the safety of consumers as well as patients. In this study, primary human peripheral blood lymphocytes of 9 donors were treated with different sub-cytotoxic concentrations of ZnO-NP for the duration of 1, 2, or 3 days. Flow cytometry was performed to investigate changes in the activation profile and the proportion of T cell subpopulations. ZnO-NP applied in this study did not induce any significant alterations in the examined markers, indicating their lack of impairment in terms of immune modulation. However, physicochemical characteristics exert a major influence on NP-associated bioactivity. To allow a precise simulation of the complex molecular processes of immune modulation, a physiological model including the different components of an immune response is needed.

Mesenchymal stromal cells (MSCs) influence tumor biology and immunology by releasing cytokines, chemokines and growth factors. Currently, cisplatin is an integral part of drug-based tumor therapy, for example, in head and neck squamous cell carcinoma (HNSCC). Cisplatin treatment induces apoptosis as a primary mechanism of action; however, additional immunomodulatory effects of cisplatin are gaining interest. The aim of this study is to evaluate the possible immunomodulatory effects of cisplatin in human MSCs (hMSCs). The MSCs, obtained from human bone marrow, were characterized by analyzing plastic adherence, typical surface features, and ability to differentiate. Toxicity analysis of cisplatin’s effects on primary MSCs, including the determination of a subtoxic concentration, was performed using the MTT assay. Enzyme-linked immunosorbent assays (ELISA) and a quantitative real-time polymerase chain reaction (qRT-PCR) were used to identify potentially immunomodulatory factors. Additionally, a scratch assay was performed to evaluate cell migration. First, subtoxic cisplatin concentrations were determined. A significantly reduced protein expression of indoleamine 2,3-dioxygenase 1 (IDO1) in MSCs under the influence of subtoxic cisplatin concentrations was demonstrated. Similarly, IL-6 protein expression was qualitatively reduced at subtoxic concentrations, although without statistical significance. At the mRNA level, qRT-PCR showed a non-significant, cisplatin concentration-dependent reduction in the expression of both IL-6 and IDO1. The scratch assay showed no statistically significant influence on migration after cisplatin treatment. In MSCs, there is tendency to a decrease in IL-6 and IDO1 at both protein and mRNA level after cisplatin exposure. These effects are congruent with each other and dose-dependent. This indicates that cisplatin not only acts via the known cytotoxic effect, but may induce a reduction in tumor-supporting proteins, like IL-6 and IDO1, by MSCs in the tumor microenvironment at subtoxic concentrations. Traditional cytostatic compounds, which can favorably modulate the immune system in the tumor microenvironment, may open new avenues to explore treatment strategies specifically targeting immunomodulation. Overall, the results indicate beneficial immunomodulation by cisplatin.

Locoregional recurrence is a major reason for therapy failure after surgical resection of head and neck squamous cell carcinoma (HNSCC). The physiological process of postoperative wound healing could potentially support the proliferation of remaining tumor cells. The aim of this study was to evaluate the influence of wound fluid (WF) on the cell cycle distribution and a potential induction of epithelial-mesenchymal transition (EMT). To verify this hypothesis, we incubated FaDu and HLaC78 cells with postoperative WF from patients after neck dissection. Cell viability in dependence of WF concentration and cisplatin was measured by flow cytometry. Cell cycle analysis was performed by flow cytometry and EMT-marker expression by rtPCR. WF showed high concentrations of interleukin (IL)-6, IL-8, IL-10, CCL2, MCP-1, EGF, angiogenin, and leptin. The cultivation of tumor cells with WF resulted in a significant increase in cell proliferation without affecting the cell cycle. In addition, there was a significant enhancement of the mesenchymal markers Snail 2 and vimentin, while the expression of the epithelial marker E-cadherin was significantly decreased. After cisplatin treatment, tumor cells incubated with WF showed a significantly higher resistance compared with the control group. The effect of cisplatin-resistance was dependent on the WF concentration. In summary, proinflammatory cytokines are predominantly found in WF. Furthermore, the results suggest that EMT can be induced by WF, which could be a possible mechanism for cisplatin resistance.

Inhalation is considered to be the most relevant source of human exposure to nanoparticles (NPs); however, only a few investigations have addressed the influence of exposing the respiratory mucosal barrier to subcytotoxic doses. In the nasal respiratory epithelium, cells of the mucosa represent one of the first contact points of the human organism with airborne NPs. Disruption of the epithelial barrier by harmful materials can lead to inflammation in addition to potential intrinsic toxicity of the particles. The aim of this study was to investigate whether subtoxic concentrations of zinc oxide (ZnO)- and silver (Ag)-NPs have an influence on upper airway barrier integrity. Nasal epithelial cells from 17 donors were cultured at the air–liquid interface and exposed to ZnO- and Ag-NPs. Barrier function, quantified by transepithelial electrical resistance (TEER), decreased after treatment with 10 µg/mL Ag-NPs, but FITC-dextran permeability remained stable and no change in mRNA levels of tight junction proteins and E-cadherin was detected by real-time quantitative PCR (RT-qPCR). The results indicate that subtoxic concentrations of Ag-NPs may already induce damage of the upper airway epithelial barrier in vitro. The lack of similar disruption by ZnO-NPs of similar size suggests a specific effect by Ag-NPs.