The effect of saliva on the fate of nanoparticles.

OBJECTIVES: The design of nanocarriers for local drug administration to the lining mucosa requires a sound knowledge of how nanoparticles (NPs) interact with saliva. This contact determines whether NPs agglomerate and become immobile due to size- and interaction-filtering effects or adsorb on the cell surface and are internalized by epithelial cells. The aim of this study was to examine the behavior of NPs in saliva considering physicochemical NP properties. MATERIALS AND METHODS: The salivary pore-size distribution was determined, and the viscosity of the fluid inside of the pores was studied with optical tweezers. Distinct functionalized NPs (20 and 200 nm) were dispersed in saliva and salivary buffers and characterized, and surface-bound MUC5B and MUC7 were analyzed by 1D electrophoresis and immunoblotting. NP mobility was recorded, and cellular uptake studies were performed with TR146 cells. RESULTS: The mode diameter of the salivary mesh pores is 0.7 µm with a peak width of 1.9 µm, and pores are filled with a low-viscosity fluid. The physicochemical properties of the NPs affected the colloidal stability and mobility: compared with non-functionalized particles, which did not agglomerate and showed a cellular uptake rate of 2.8%, functionalized particles were immobilized, which was correlated with agglomeration and increased binding to mucins. CONCLUSION: The present study showed that the salivary microstructure facilitates NP adsorption. However, NP size and surface functionalization determine the colloidal stability and cellular interactions. CLINICAL RELEVANCE: The sound knowledge of NP interactions with saliva enables the improvement of current treatment strategies for inflammatory oral diseases.

Rational Design and Characterization of a Nanosuspension for Intraoral Administration Considering Physiological Conditions.

The oral cavity displays an attractive route in drug administration that is not associated with gastric transit and hepatic first-pass metabolism. However, limiting factors for an efficient transit of drugs through the oral mucosa are poor water solubility and permeability. Hence, various strategies exist to enhance solubility. Specifically, nanotechnology has attracted much research interest in the past decade. This study aimed at developing a stable nanosuspension of the model compound phenytoin via wet media milling. The nanosuspensions were carefully characterized regarding hydrodynamic particle sizes, crystallinity, and dissolution characteristics under nonphysiological or physiological (salivary) conditions. The permeability of bulk phenytoin and nanophenytoin through a buccal in vitro and ex vivo model was investigated, and the apparent permeability coefficients were determined. Moreover, cytotoxicity studies were conducted. The addition of Tween 80 as stabilizer resulted in a stable crystalline nanosuspension (330 nm). The solubility characteristics significantly increased under salivary conditions, which further impacted the permeability, as the steady state appearance rate of nanosized phenytoin was 1.4-fold higher. Cytotoxicity studies demonstrated that bulk-/nano-phenytoin exhibited no harmful effects. It can be concluded that the salivary environment (i.e., ionic strength, pH) strongly impacts the solubility and consequently the permeability of crystalline nanosuspensions across the buccal mucosa.

Interactions between nano-TiO2 and the oral cavity: impact of nanomaterial surface hydrophilicity/hydrophobicity.

Titanium dioxide (TiO2) nanoparticles are available in a variety of oral applications, such as food additives and cosmetic products. Thus, questions about their potential impact on the oro-gastrointestinal route rise. The oral cavity represents the first portal of entry and is known to rapidly interact with nanoparticles. Surface charge and size contribute actively to the particle-cell interactions, but the influence of surface hydrophilicity/hydrophobicity has never been shown before. This study addresses the biological impact of hydrophilic (NM 103, rutile, 20 nm) and hydrophobic (NM 104, rutile, 20 nm) TiO2 particles within the buccal mucosa. Particle characterization was addressed with dynamic light scattering and laser diffraction. Despite a high agglomeration tendency, 10% of the particles/agglomerates were present in the nanosized range and penetrated into the mucosa, independent of the surface properties. However, significant differences were observed in intracellular particle localization. NM 104 particles were found freely distributed in the cytoplasm, whereas their hydrophobic counterparts were engulfed in vesicular structures. Although cell viability/membrane integrity was not affected negatively, screening assays demonstrated that NM 104 particles showed a higher potential to decrease the physiological mitochondrial membrane potential than NM 103, resulting in a pronounced generation of reactive oxygen species.

The oral cavity as a biological barrier system: design of an advanced buccal in vitro permeability model.

An important area for future research lies in finding a drug delivery system across or into the oral mucosa. However, to design such systems, simplified biological models are necessary so that the mechanisms and/or interactions of interest can readily be studied. The oral epithelium is covered by a complex mucus layer, which enables exchange of nutrients and provides lubrication. However, it has been demonstrated that mucus has an impact on the mobility of nanoparticles and drug molecules. Thus, we aimed to develop an advanced buccal in vitro model for studying transport of nanoparticles, taking the mucus layer into account. First, animal mucins (porcine gastric, bovine submaxillary) were compared with natural human mucin regarding chemical and morphological structure. Second, an "external" mucus layer was prepared by a film method and deposited onto an oral cell line (TR 146), cultured on transwells®. Adherence of the mucin fibers was evaluated and the viability of the model was assessed. Nanoparticle transport studies were performed with this advanced in vitro model and an ex vivo diffusion system. The results revealed that porcine mucin is most similar to human natural mucin in chemical structure and morphology. Both the bovine and porcine mucin fibers adhered onto the oral cells: Due to the different morphology of bovine mucin, the viability of the oral cells decreased, whereas porcine mucin maintained the viability of the model for more than 48 h. Comparison of in vitro data with ex vivo data suggested reliability of the advanced buccal in vitro model. Additionally, it was demonstrated that the mucus layer in the oral cavity also acts as a strong barrier for the mobility of nanoparticles.