Interaction of nanoparticles with the pulmonary surfactant system

Adverse biophysical effects of hydroxyapatite nanoparticles on natural pulmonary surfactant

Inhaled nanoparticles (NPs) must first interact with the pulmonary surfactant (PS) lining layer that covers the entire internal surface of the respiratory tract and plays an important role in surface tension reduction and host defense. Interactions with the PS film determine the subsequent clearance, retention, and translocation of the inhaled NPs and hence their potential toxicity. To date, little is known how NPs interact with PS, and whether or not NPs have adverse effects on the biophysical function of PS. We found a time-dependent toxicological effect of hydroxyapatite NPs (HA-NPs) on a natural PS, Infasurf, and the time scale of surfactant inhibition after particle exposure was comparable to the turnover period of surfactant metabolism. Using a variety of in vitro biophysicochemical characterization techniques, we have determined the inhibition mechanism to be due to protein adsorption onto the HA-NPs. Consequently, depletion of surfactant proteins from phospholipid vesicles caused conversion of original large vesicles into much smaller vesicles with poor surface activity. These small vesicles, in turn, inhibited biophysical function of surfactant films after adsorption at the air-water interface. Cytotoxicity study found that the HA-NPs at the studied concentration were benign to human bronchial epithelial cells, thereby highlighting the importance of evaluating biophysical effect of NPs on PS. The NP-PS interaction mechanism revealed by this study may not only provide new insight into the toxicological study of nanoparticles but also shed light on the feasibility of NP-based pulmonary drug delivery.

Proteomic characterization of engineered nanomaterial-protein interactions in relation to surface reactivity

Adsorption of proteins onto an engineered nanoparticle surface happens immediately after particles come in contact with a biological fluid. However, at the moment very little is known about the mechanisms of interactions between biomolecules and nanomaterials. In this study, eleven thoroughly characterized materials were first investigated in vitro for their ability to enter human lung epithelial cells and human monocyte-derived macrophages. All tested materials were taken up by primary macrophages and epithelial cells. Some of the engineered nanomaterials (ENM) were found in the cytoplasm. Large quantitative and qualitative variation in the binding efficiencies to cellular proteins was observed between different tested nanoparticles. Pulmonary surfactant components significantly reduced the overall protein adsorption on the surface of ENMs. Fibrinogen chains were attached to all materials after exposure to plasma proteins. Common ENM-bound cytoplasmic protein identifications were peroxiredoxin 1, annexin A2, and several ribosomal and cytoskeletal proteins. The underlying mechanism of the ENM-plasma protein interaction may diverge from that of cell lysate proteins, as the binding efficiency to cell lysate proteins appears to depend on the characteristics of the ENM surface, whereas the adsorbed plasma proteins are involved in particle phagocytosis and seem to cover ENMs independently of the their surface properties. Identification of the composition of the nanomaterial-protein complex is crucial for understanding of the uptake mechanisms, biodistribution, and clearance of ENMs, knowledge which is required for safety evaluation and biomedical applications of these materials.

The influence of pulmonary surfactant on nanoparticulate drug delivery systems

The pulmonary route is very attractive for drug delivery by inhalation. In this regard, nanoparticulate drug delivery systems, designed as multifunctional engineered nanoparticles, are very promising since they combine several opportunities like a rather uniform distribution of drug dose among all ventilated alveoli allowing for uniform cellular drug internalization. However, although the field of nanomedicine offers multiple opportunities, it still is in its infancy and the research has to proceed in order to obtain a specific targeting of the drug combined with minimum side effects. If inhaled nanoparticulate drug delivery systems are deposited on the pulmonary surfactant, they come into contact with phospholipids and surfactant proteins. It is highly likely that the interaction of nanoparticulate drug delivery systems with surfactant phospholipids and proteins will be able to mediate/modulate the further fate of this specific drug delivery system. In the present comment, we discuss the potential interactions of nanoparticulate drug delivery systems with pulmonary surfactant as well as the potential consequences of this interaction.

Effect of sonication and serum proteins on copper release from copper nanoparticles and the toxicity towards lung epithelial cells

Abstract Different methodological settings can influence particle characteristics and toxicity in nanotoxicology. The aim of this study was to investigate how serum proteins and sonication of Cu nanoparticle suspensions influence the properties of the nanoparticles and toxicological responses on human lung epithelial cells. This was investigated by using methods for particle characterization (photon correlation spectroscopy and TEM) and Cu release (atomic absorption spectroscopy) in combination with assays for analyzing cell toxicity (MTT-, trypan blue- and Comet assay). The results showed that sonication of Cu nanoparticles caused decreased cell viability and increased Cu release compared to non-sonicated particles. Furthermore, serum in the cell medium resulted in less particle agglomeration and increased Cu release compared with medium without serum, but no clear difference in toxicity was detected. Few cells showed intracellular Cu nanoparticles due to fast release/dissolution processes of Cu. In conclusion; sonication can affect the toxicity of nanoparticles.

Interaction of metal oxide nanoparticles with lung surfactant protein A

The alveolar lining fluid (ALF) covering the respiratory epithelium of the deep lung is the first biological barrier encountered by nanoparticles after inhalation. We here report for the first time significant differences for metal oxide nanoparticles to the binding of surfactant protein A (SP-A), the predominant protein component of ALF. SP-A is a physiologically most relevant protein and provides important biological signals. Also, it is involved in the lung's immune defence, controlling e.g. particle binding, uptake or transcytosis by epithelial cells and macrophages. In our study, we could prove different particle-protein interaction for eight different nanoparticles, whereas particles of the same bulk material revealed different adsorption patterns. In contrast to other proteins as bovine serum albumin (BSA), SP-A does not seem to significantly deagglomerate large agglomerates of particles, indicating different adsorption mechanisms as in the well-investigated model protein BSA. These findings may have important consequences for biological fate and toxicological effects of inhaled nanomaterials.

Allergen particle binding by human primary bronchial epithelial cells is modulated by surfactant protein D

Background

Allergen-containing subpollen particles (SPP) are released from whole plant pollen upon contact with water or even high humidity. Because of their size SPP can preferentially reach the lower airways where they come into contact with surfactant protein (SP)-D. Our previous work demonstrated that SP-D increases the uptake of SPP by alveolar macrophages. In the present study, we investigated the uptake of SPP in human primary epithelial cells and the potential modulation by SP-D. The patho-physiological consequence was evaluated by measurement of pro-inflammatory mediators.

Methods

SPP were isolated from timothy grass and subsequently fluorescently labelled. Human primary bronchial epithelial cells were incubated with SPP or polystyrene particles (PP) in the presence and absence of surfactant protein D. In addition, different sizes and surface charges of the PP were studied. Particle uptake was evaluated by flow cytometry and confocal microscopy. Soluble mediators were measured by enzyme linked immunosorbent assay or bead array.

Results

SPP were taken up by primary epithelial cells in a dose dependent manner. This uptake was coincided with secretion of Interleukin (IL)-8. SP-D increased the fraction of bronchial epithelial cells that bound SPP but not the fraction of cells that internalized SPP. SPP-induced secretion of IL-8 was further increased by SP-D. PP were bound and internalized by epithelial cells but this was not modulated by SP-D.

Conclusions

Epithelial cells bind and internalize SPP and PP which leads to increased IL-8 secretion. SP-D promotes attachment of SPP to epithelial cells and may thus be involved in the inflammatory response to inhaled allergen.

Nanoparticle interaction with model lung surfactant monolayers

One of the most important functions of the lung surfactant monolayer is to form the first line of defence against inhaled aerosols such as nanoparticles (NPs), which remains largely unexplored. We report here, for the first time, the interaction of polyorganosiloxane NPs (AmorSil20: 22 nm in diameter) with lipid monolayers characteristic of alveolar surfactant. To enable a better understanding, the current knowledge about an established model surface film that mimics the surface properties of the lung is reviewed and major results originating from our group are summarized. The pure lipid components dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylglycerol have been used to study the biophysical behaviour of their monolayer films spread at the air-water interface in the presence of NPs. Film balance measurements combined with video-enhanced fluorescence microscopy have been used to investigate the formation of domain structures and the changes in the surface pattern induced by NPs. We are able to show that NPs are incorporated into lipid monolayers with a clear preference for defect structures at the fluid-crystalline interface leading to a considerable monolayer expansion and fluidization. NPs remain at the air-water interface probably by coating themselves with lipids in a self-assembly process, thereby exhibiting hydrophobic surface properties. We also show that the domain structure in lipid layers containing surfactant protein C, which is potentially responsible for the proper functioning of surfactant material, is considerably affected by NPs.

The effect of titanium dioxide nanoparticles on pulmonary surfactant function and ultrastructure

BACKGROUND

Pulmonary surfactant reduces surface tension and is present at the air-liquid interface in the alveoli where inhaled nanoparticles preferentially deposit. We investigated the effect of titanium dioxide (TiO(2)) nanosized particles (NSP) and microsized particles (MSP) on biophysical surfactant function after direct particle contact and after surface area cycling in vitro. In addition, TiO(2) effects on surfactant ultrastructure were visualized.

METHODS

A natural porcine surfactant preparation was incubated with increasing concentrations (50-500 microg/ml) of TiO(2) NSP or MSP, respectively. Biophysical surfactant function was measured in a pulsating bubble surfactometer before and after surface area cycling. Furthermore, surfactant ultrastructure was evaluated with a transmission electron microscope.

RESULTS

TiO(2) NSP, but not MSP, induced a surfactant dysfunction. For TiO(2) NSP, adsorption surface tension (gammaads) increased in a dose-dependent manner from 28.2 + or - 2.3 mN/m to 33.2 + or - 2.3 mN/m (p < 0.01), and surface tension at minimum bubble size (gammamin) slightly increased from 4.8 + or - 0.5 mN/m up to 8.4 + or - 1.3 mN/m (p < 0.01) at high TiO(2) NSP concentrations. Presence of NSP during surface area cycling caused large and significant increases in both gammaads (63.6 + or - 0.4 mN/m) and gammamin (21.1 + or - 0.4 mN/m). Interestingly, TiO(2) NSP induced aberrations in the surfactant ultrastructure. Lamellar body like structures were deformed and decreased in size. In addition, unilamellar vesicles were formed. Particle aggregates were found between single lamellae.

CONCLUSION

TiO(2) nanosized particles can alter the structure and function of pulmonary surfactant. Particle size and surface area respectively play a critical role for the biophysical surfactant response in the lung.