Size and phase preservation of amorphous calcium carbonate nanoparticles in aqueous media using different types of lignin for contrast-enhanced ultrasound imaging

HYPOTHESIS

Calcium carbonate (CaCO3) nanoparticles could have great potential for contrast-enhanced ultrasound imaging (CEUS) due to their gas-generating properties and sensitivity to physiological conditions. However, the use of nano CaCO3 for biomedical applications requires the assistance of stabilizers to control the size and avoid the fast dissolution/recrystallization of the particles when exposed to aqueous conditions.

EXPERIMENTS

Herein, we report the stabilization of nano CaCO3 using lignin, and synthesized core-shell amorphous CaCO3-lignin nanoparticles (LigCC NPs) with a diameter below 100 nm. We have then investigated the echogenicity of the LigCC NPs by monitoring the consequent generation of contrast in vitro for 90 min in linear and non-linear B-mode imaging.

FINDINGS

This research explores how lignin type and structure affect stabilization efficiency, lignin structuration around CaCO3 cores, and particle echogenicity. Interestingly, by employing lignin as the stabilizer, it becomes possible to maintain the echogenic properties of CaCO3, whereas the use of lipid coatings prevents the production of signal generation in ultrasound imaging. This work opens new avenue for CEUS imaging of the vascular and extravascular space using CaCO3, as it highlights the potential to generate contrast for extended durations at physiological pH by utilizing the amorphous phase of CaCO3.

Culturing Human Lung Adenocarcinoma Cells in a Serum-Free Environment

The human lung adenocarcinoma cell line A549 is commonly used in cancer research as a model of malignant alveolar type II epithelial cells. A549 cells are frequently cultured in Ham's F12K (Kaighn's) or Dulbecco's Modified Eagle's Medium (DMEM), supplemented with glutamine and 10% fetal bovine serum (FBS). However, the use of FBS presents significant scientific concerns, such as the presence of undefined components and batch-to-batch variation leading to possible reproducibility issues in experiments and readouts. This chapter describes how to transition A549 cells to FBS-free medium and gives some insights on the further characterizations and functionality assays that would be necessary to perform for the validation of the cultured cells.

Maximizing the relevance and reproducibility of A549 cell culture using FBS-free media

Scientists are using in vitro methods to answer important research questions and implementing strategies to maximize the reliability and human relevance of these methods. One strategy is to replace the use of fetal bovine serum (FBS)-an undefined and variable mixture of biomolecules-in cell culture media with chemically defined or xeno-free medium. In this study, A549 cells, a human lung alveolar-like cell line commonly used in respiratory research, were transitioned from a culture medium containing FBS to media without FBS. A successful transition was determined based on analysis of cell morphology and functionality. Following transition to commercially available CnT-Prime Airway (CELLnTEC) or X-VIVO™ 10 (Lonza) medium, the cells were characterized by microscopic evaluation and calculation of doubling time. Their genotype, morphology, and functionality were assessed by monitoring the expression of gene markers for lung cell types, surfactant production, cytokine release, the presence of multilamellar bodies, and cell viability following sodium dodecyl sulphate exposure. Our results showed that A549 cells successfully transitioned to FBS-free media under submerged and air-liquid-interface conditions. Cells grown in X-VIVO™ 10 medium mimicked cellular characteristics of FBS-supplemented media while those grown in CnT-Prime Airway medium demonstrated characteristics possibly more reflective of normal human alveolar epithelial cells.

In vitro exposure of a 3D-tetraculture representative for the alveolar barrier at the air-liquid interface to silver particles and nanowires

BACKGROUND

The present study aimed to evaluate the potential differences in the biological effects of two types of spherical silver particles of 20 and 200 nm (Ag20 and Ag200), and of PVP-coated silver nanowires (AgNWs) with a diameter of 50 nm and length up to 50 μm, using a complex 3D model representative for the alveolar barrier cultured at air-liquid interface (ALI). The alveolar model was exposed to 0.05, 0.5 and 5 μg/cm2 of test compounds at ALI using a state-of-the-art exposure system (Vitrocell™Cloud System). Endpoints related to the oxidative stress induction, anti-oxidant defence mechanisms, pro-inflammatory responses and cellular death were selected to evaluate the biocompatibility of silver particles and nanowires (AgNMs) and to further ascribe particular biological effects to the different morphologic properties between the three types of AgNMs evaluated.

RESULTS

Significant cytotoxic effect was observed for all three types of AgNMs at the highest tested doses. The increased mRNA levels of the pro-apoptotic gene CASP7 suggests that apoptosis may occur after exposure to AgNWs. All three types of AgNMs increased the mRNA level of the anti-oxidant enzyme HMOX-1 and of the metal-binding anti-oxidant metallothioneins (MTs), with AgNWs being the most potent inducer. Even though all types of AgNMs induced the nuclear translocation of NF-kB, only AgNWs increased the mRNA level of pro-inflammatory mediators. The pro-inflammatory response elicited by AgNWs was further confirmed by the increased secretion of the 10 evaluated interleukins.

CONCLUSION

In the current study, we demonstrated that the direct exposure of a complex tetra-culture alveolar model to different types of AgNMs at ALI induces shape- and size-specific biological responses. From the three AgNMs tested, AgNWs were the most potent in inducing biological alterations. Starting from 50 ng/cm2, a dose representative for an acute exposure in a high exposure occupational setting, AgNWs induced prominent changes indicative for a pro-inflammatory response. Even though the acute responses towards a dose representative for a full-lifetime exposure were also evaluated, chronic exposure scenarios at low dose are still unquestionably needed to reveal the human health impact of AgNMs during realistic conditions.

An in vitro coculture system for the detection of sensitization following aerosol exposure

The aim of the study was to develop an in vitro model that mimics the alveolar-capillary barrier and that allows assessment of the respiratory sensitizing potential of respiratory sensitizers. The 3D in vitro model cultured at the air liquid interface consists of alveolar type II epithelial cells (A549), endothelial cells (EA.hy926), macrophage-like cells (PMA-differentiated THP-1) and dendritic-like cells (non-differentiated THP-1). This alveolar model was exposed apically to nebulized chemical respiratory sensitizers (Phthalic Anhydride (PA) and TriMellitic Anhydride (TMA)) or irritants (Methyl Salicylate (MeSa) and Acrolein (Acr)) at concentrations inducing at maximum 25% of cytotoxicity. The exposure to respiratory sensitizers induced dendritic cells activation and a specific cytokine release pattern, while the irritants did not. In addition, the cell surface marker OX40L was determined for dendritic like cells activation to identify high molecular weight allergens. With this in vitro model we can postulate a set of promising markers based on the studied compounds that allow the discrimination of chemical respiratory sensitizers from irritants.

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.

Endothelial responses of the alveolar barrier in vitro in a dose-controlled exposure to diesel exhaust particulate matter

BACKGROUND

During the last 250 years, the level of exposure to combustion-derived particles raised dramatically in western countries, leading to increased particle loads in the ambient air. Among the environmental particles, diesel exhaust particulate matter (DEPM) plays a special role because of its omnipresence and reported effects on human health. During recent years, a possible link between air pollution and the progression of atherosclerosis is recognized. A central effect of DEPM is their impact on the endothelium, especially of the alveolar barrier. In the present study, a complex 3D tetraculture model of the alveolar barrier was used in a dose-controlled exposure scenario with realistic doses of DEPM to study the response of endothelial cells.

RESULTS

Tetracultures were exposed to different doses of DEPM (SRM2975) at the air-liquid-interface. DEPM exposure did not lead to the mRNA expression of relevant markers for endothelial inflammation such as ICAM-1 or E-selectin. In addition, we observed neither a significant change in the expression levels of the genes relevant for antioxidant defense, such as HMOX1 or SOD1, nor the release of pro-inflammatory second messengers, such as IL-6 or IL-8. However, DEPM exposure led to strong nuclear translocation of the transcription factor Nrf2 and significantly altered expression of CYP1A1 mRNA in the endothelial cells of the tetraculture.

CONCLUSION

In the present study, we demonstrated the use of a complex 3D tetraculture system together with a state-of-the-art aerosol exposure equipment to study the effects of in vivo relevant doses of DEPM on endothelial cells in vitro. To the best of our knowledge, this study is the first that focuses on indirect effects of DEPM on endothelial cells of the alveolar barrier in vitro. Exposure to DEPM led to significant activation and nuclear translocation of the transcription factor Nrf2 in endothelial cells. The considerably low doses of DEPM had a low but measurable effect, which is in line with recent data from in vivo studies.