On the Structure, Stability, and Cell Uptake of Nanostructured Lipid Carriers for Drug Delivery.

The efficacy of nanostructured lipid carriers (NLC) for drug delivery strongly depends on their stability and cell uptake. Both properties are governed by their compositions and internal structure. To test the effect of the lipid composition of NLC on cell uptake and stability, three kinds of liquid lipids with different degrees of unsaturation are employed. After ensuring homogeneous size distributions, the thermodynamic characteristics, stability, and mixing properties of NLC are characterized. Then the rates and predominant pathways of cell uptake are determined. Although the same surfactant is used in all cases, different uptake rates are observed. This finding contradicts the view that the surface properties of NLC are dominated by the surfactant. Instead, the uptake rates are explained by the structure of the nanocarrier. Depending on the mixing properties, some liquid lipids remain inside the nanocarrier, while other liquid lipids are present on the surface. Nanocarriers with liquid lipids on the surface are taken up more readily by the cells. This shows that the engineering of efficient lipid nanocarriers requires a delicate balance of interactions between all components of the nanocarrier on the molecular level.

In Vitro and In Vivo Evaluation of Carbopol 71G NF-Based Mucoadhesive Minitablets as a Gastroretentive Dosage Form.

Gastroretentive dosage forms are intended to stay inside the stomach for a long period of time while releasing an active pharmaceutical ingredient. Such systems may offer significant benefits for numerous drugs compared to other sustained release systems, such as improved pharmacokinetics/bioavailability and reduced intake frequency and thereby improved adherence to the medical therapy. However, there is no gastroretentive product on the market with proven reliable gastroretentive properties in humans. A major obstacle is the motility pattern of the stomach in the fasting state in humans, which reliably ensures gastric emptying of even large indigestible objects into the small intestine. One promising approach to avoid gastric emptying is adhesion of the drug delivery system to the gastric mucosa. In order to achieve mucoadhesive properties, minitablets containing Carbopol 71G NF were developed and compared to minitablets without adhesive properties. In a specialized mucoadhesive test system, the adhesion time was prolonged for adhesive minitablets (240 min) compared to non-adhesive minitablets (30 min). The in vivo transit behavior was investigated using magnetic resonance imaging in 11 healthy volunteers in fasted state in a crossover setup. It was found that the gastric residence time (GRT) of the adhesive minitablets (median of 37.5 min with IQR = 22.5-52.5) was statistically significantly prolonged compared to the non-adhesive minitablets (median of 7.5 with IQR = 7.5-22.5), indicating a delay in gastric emptying by adhesion to the gastric mucosa. However, the system needs further improvement to create a clinical benefit. Furthermore, it was observed that for 9 of 22 administrations (three minitablets were given simultaneously with every administration), the minitablets were not emptied together but showed different GRTs.

The Role of Local Inflammation and Hypoxia in the Formation of Hypertrophic Scars-A New Model in the Duroc Pig.

Hypertrophic scars continue to be a major burden, especially after burns. Persistent inflammation during wound healing appears to be the precipitating aspect in pathologic scarring. The lack of a standardized model hinders research from fully elucidating pathophysiology and therapy, as most therapeutic approaches have sparse evidence. The goal of this project was to investigate the mechanisms of scar formation after prolonged wound inflammation and to introduce a method for generating standardized hypertrophic scars by inducing prolonged inflammation. Four wound types were created in Duroc pigs: full-thickness wounds, burn wounds, and both of them with induced hyperinflammation by resiquimod. Clinical assessment (Vancouver Scar Scale), tissue oxygenation by hyperspectral imaging, histologic assessment, and gene expression analysis were performed at various time points during the following five months. Native burn wounds as well as resiquimod-induced full-thickness and burn wounds resulted in more hypertrophic scars than full-thickness wounds. The scar scale showed significantly higher scores in burn- and resiquimod-induced wounds compared with full-thickness wounds as of day 77. These three wound types also showed relative hypoxia compared with uninduced full-thickness wounds in hyperspectral imaging and increased expression of HIF1a levels. The highest number of inflammatory cells was detected in resiquimod-induced full-thickness wounds with histologic features of hypertrophic scars in burn and resiquimod-induced wounds. Gene expression analysis revealed increased inflammation with only moderately altered fibrosis markers. We successfully created hypertrophic scars in the Duroc pig by using different wound etiologies. Inflammation caused by burns or resiquimod induction led to scars similar to human hypertrophic scars. This model may allow for the further investigation of the exact mechanisms of pathological scars, the role of hypoxia and inflammation, and the testing of therapeutic approaches.

Investigation of Hydrocolloid Plant Polysaccharides as Potential Candidates to Mimic the Functions of MUC5B in Saliva.

The successful substitution of complex physiological fluids, such as human saliva, remains a major challenge in drug development. Although there are a large number of saliva substitutes on the market, their efficacy is often inadequate due to short residence time in the mouth, unpleasant mouthfeel, or insufficient protection of the teeth. Therefore, systems need to be identified that mimic the functions of saliva, in particular the salivary mucin MUC5B and the unique physiological properties of saliva. To this end, plant extracts known to contain hydrocolloid polysaccharides and to have mucus-forming properties were studied to evaluate their suitability as saliva substitutes. The aqueous plant extracts of Calendula officinalis, Fucus sp. thalli, and lichenan from Lichen islandicus were examined for composition using a range of techniques, including GC-MS, NMR, SEC, assessment of pH, osmolality, buffering capacity, viscoelasticity, viscoelastic interactions with human saliva, hydrocolloid network formation, and in vitro cell adhesion. For this purpose, a physiologically adapted adhesive test was developed using human buccal epithelial cells. The results show that lichenan is the most promising candidate to mimic the properties of MUC5B. By adjusting the pH, osmolality, and buffering capacity with K2HPO4, it was shown that lichenan exhibited high cell adhesion, with a maximum detachment force that was comparable to that of unstimulated whole mouth saliva.

Investigation of the Influence of Wound-Treatment-Relevant Buffer Systems on the Colloidal and Optical Properties of Gold Nanoparticles.

Biocompatible gold nanoparticles (AuNPs) are used in wound healing due to their radical scavenging activity. They shorten wound healing time by, for example, improving re-epithelialization and promoting the formation of new connective tissue. Another approach that promotes wound healing through cell proliferation while inhibiting bacterial growth is an acidic microenvironment, which can be achieved with acid-forming buffers. Accordingly, a combination of these two approaches appears promising and is the focus of the present study. Here, 18 nm and 56 nm gold NP (Au) were prepared with Turkevich reduction synthesis using design-of-experiments methodology, and the influence of pH and ionic strength on their behaviour was investigated. The citrate buffer had a pronounced effect on the stability of AuNPs due to the more complex intermolecular interactions, which was also confirmed by the changes in optical properties. In contrast, AuNPs dispersed in lactate and phosphate buffer were stable at therapeutically relevant ionic strength, regardless of their size. Simulation of the local pH distribution near the particle surface also showed a steep pH gradient for particles smaller than 100 nm. This suggests that the healing potential is further enhanced by a more acidic environment at the particle surface, making this strategy a promising approach.

Thiolated Chitosan Conjugated Liposomes for Oral Delivery of Selenium Nanoparticles.

This study aimed to design a hybrid oral liposomal delivery system for selenium nanoparticles (Lip-SeNPs) to improve the bioavailability of selenium. Thiolated chitosan, a multifunctional polymer with mucoadhesive properties, was used for surface functionalization of Lip-SeNPs. Selenium nanoparticle (SeNP)-loaded liposomes were manufactured by a single step microfluidics-assisted chemical reduction and assembling process. Subsequently, chitosan-N-acetylcysteine was covalently conjugated to the preformed Lip-SeNPs. The Lip-SeNPs were characterized in terms of composition, morphology, size, zeta potential, lipid organization, loading efficiency and radical scavenging activity. A co-culture system (Caco-2:HT29-MTX) that integrates mucus secreting and enterocyte-like cell types was used as a model of the human intestinal epithelium to determine adsorption, mucus penetration, release and transport properties of Lip-SeNPs in vitro. Thiolated Lip-SeNPs were positively charged with an average size of about 250 nm. Thiolated Lip-SeNPs tightly adhered to the mucus layer without penetrating the enterocytes. This finding was consistent with ex vivo adsorption studies using freshly excised porcine small intestinal tissues. Due to the improved mucoadhesion and retention in a simulated microenvironment of the small intestine, thiolated Lip-SeNPs might be a promising tool for oral selenium delivery.

Interaction of Differently Coated Silver Nanoparticles With Skin and Oral Mucosal Cells.

Silver nanoparticles (AgNP) can be found in different consumer products and various medical devices due to their excellent biocidal properties. Despite extensive scientific literature reporting biological effects of AgNP, there is still a lack of scientific evidence on how different surface functionalization affects AgNP interaction with the human skin and the oral epithelium. This study aimed to investigate biological consequences following the treatment of HaCaT and TR146 cells with AgNP stabilized with negatively charged sodium bis(2-ethylhexyl)-sulfosuccinate (AOT), neutral polyvinylpyrrolidone (PVP), and positively charged poly-l-lysine (PLL). All AgNP were characterized by means of size, shape and surface charge. Interactions with biological barriers were investigated in vitro by determining cell viability, particle uptake, oxidative stress response and DNA damages following AgNP treatment. Results showed a significant difference in cytotoxicity depending on the surface coating used for AgNP stabilization. All three types of AgNP induced apoptosis, oxidative stress response and DNA damages in cells, but AOT- and PVP-coated AgNP exhibited lower toxicity than positively charged PLL-AgNP. Considering the number of data gaps related to the safe use of nanomaterials in biomedicine, this study highlights the importance of particle surface functionalization that should be considered during design and development of future AgNP-based medical products.

Cytokine-Mediated Inflammation in the Oral Cavity and Its Effect on Lipid Nanocarriers.

Topical drug administration to the oral mucosa proves to be a promising treatment alternative for inflammatory diseases. However, disease-related changes in the cell barrier must be considered when developing such delivery systems. This study aimed at investigating the changes in the lining mucosa caused by inflammation and evaluating the consequences on drug delivery systems such as nanostructured lipid carriers (NLC). For this, TR146 cells were treated with inflammatory cytokines and bacterial components. Cell viability and integrity, reactive oxygen species (ROS), and interleukin (IL)-8 release were used as endpoints to assess inflammation. Translocation of phosphatidylserine, cytoskeletal arrangement, opening of desmosomes, and cell proliferation were examined. Transport studies with NLC were performed considering active and passive pathways. The results showed that IL-1ß and tumor necrosis factor α induced inflammation by increasing IL-8 and ROS production (22-fold and 2-fold). Morphologically, loss of cell-cell connections and formation of stress fibers and hyperplasia were observed. The charge of the cell membrane shifted from neutral to negative, which increased the absorption of NLC due to the repulsive interactions between the hydrophobic negative particles and the cell membrane on the one hand, and interactions with lipophilic membrane proteins such as caveolin on the other.

Impact of surface functionalization on the toxicity and antimicrobial effects of selenium nanoparticles considering different routes of entry.

Selenium nanoparticles (SeNPs) were first designed as nutritional supplements, but they are attractive also for use in diagnostic and therapeutic systems owing to their biocompatibility and protective effects. This study aimed to examine if different SeNPs stabilization strategies affect their (i) antimicrobial activity against bacteria Escherichia coli and Staphylococcus aureus and yeast Saccharomyces cerevisiae and (ii) toxicity to human cells of different biological barriers i.e., skin, oral and intestinal mucosa. For surface stabilization, polyvinylpyrrolidone (PVP), poly-L-lysine (PLL) and polyacrylic acid (PAA) were used rendering neutral, positively and negatively charged SeNPs, respectively. The SeNPs (primary size ~80 nm) showed toxic effects in human cells in vitro and in bacteria S. aureus, but not in E. coli and yeast S. cerevisiae. Toxicity of SeNPs (24 h IC50) ranged from 1.4 to >100 mg Se/L, depending on surface functionalization (PLL > PAA > PVP) and was not caused by ionic Se. At subtoxic concentrations, all SeNPs were taken up by all human cell types, induced oxidative stress response and demonstrated genotoxicity. As the safety profile of SeNPs was dependent not only on target cells (mammalian cells, bacteria, yeast), but also on surface functionalization, these aspects should be considered during development of novel SeNPs-based biomedical products.

Comprehensive characterization of nanostructured lipid carriers using laboratory and synchrotron X-ray scattering and diffraction.

The development of lipid nanoparticles requires knowledge on the crystalline structure, polymorphic transitions and lipid-drug interactions. This study aimed at introducing advanced techniques to characterize nanostructured lipid carriers (NLC) comprising palmitic acid, oleic acid, stabilizer and Domperidone. Crystallinity of single components and mixtures was investigated by laboratory Small Angle X-ray Scattering (SAXS). NLC were studied with laboratory Small and Wide Angle X-ray Scattering (SWAXS). Photon Correlation Spectroscopy and Freeze Fracture Transmission Electron Microscopy were used to monitor particle size, zeta potential and shape. Stability of NLC was investigated using synchrotron X-ray Diffraction (XRD) and SAXS and laboratory SAXS. Palmitic acid showed a lamellar structure (polymorph C), which was still present after particle preparation. Spherical 300 nm-sized particles with zeta potential values above -30 mV were obtained and Domperidone was incorporated in its amorphous form. During storage, no differences in synchrotron XRD spectra were seen. However, laboratory SAXS measurements showed a second lamellar structure, identified as polymorph B. Synchrotron SAXS temperature scans confirmed that polymorph B did not affect the morphology of the encapsulated drug or the shape of NLC. These results highlight the unique capabilities of laboratory and synchrotron X-ray Scattering and Diffraction for improved structural characterization of lipid nanoparticles.

Development of nanostructured lipid carriers for intraoral delivery of Domperidone.

The oral cavity displays one potentially attractive route that is not associated with gastric transit and hepatic first pass metabolism. However, poorly soluble active candidates require a drug delivery system to facilitate their transport through oral biological membranes. To this end, nanostructured lipid carriers (NLC) were loaded with Domperidone and produced with high pressure homogenization. NLC were characterized regarding particle size, particle size distribution, zeta potential, entrapment efficiency and crystallinity. Moreover, permeability studies through the buccal mucosa were performed using in-vitro and ex-vivo models. Palmitic acid (solid lipid) and oleic acid (liquid lipid) in the ratio 9:1 were able to dissolve the highest amount of Domperidone. Particle diameters of about 280nm and monomodal size distribution were obtained. A zeta potential higher than -30mV was observed over a period of 28days indicating good physical stability. NLC dispersed in saliva did not agglomerate and were actively internalized by buccal TR 146 cells without causing adverse side effects. Ex-vivo studies confirmed that Domperidone permeated the entire tissue. This leads to the conclusion that NLC are appropriate carrier systems that facilitate the transport of poorly soluble drugs across buccal and sublingual tissue.

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.

Nano-extrusion: a promising tool for continuous manufacturing of solid nano-formulations.

Since more than 40% of today's drugs have low stability, poor solubility and/or limited ability to cross certain biological barriers, new platform technologies are required to address these challenges. This paper describes a novel continuous process that converts a stabilized aqueous nano-suspension into a solid oral formulation in a single step (i.e., the NANEX process) in order to improve the solubility of a model drug (phenytoin). Phenytoin nano-suspensions were prepared via media milling using different stabilizers. A stable nano-suspension was obtained using Tween(®) 80 as a stabilizer. The matrix material (Soluplus(®)) was gravimetrically fed into the hot melt extruder. The suspension was introduced through a side feeding device and mixed with the molten polymer to immediately devolatilize the water in the nano-suspension. Phenytoin nano-crystals were dispersed and embedded in the molten polymer. Investigation of the nano-extrudates via transmission electron microscopy and atomic force microscopy showed that the nano-crystals were embedded de-aggregated in the extrudates. Furthermore, no changes in the crystallinity (due to the mechanical and thermal stress) occurred. The dissolution studies confirmed that the prepared nano-extrudates increased the solubility of nano-crystalline phenytoin, regardless of the polymer. Our work demonstrates that NANEX represents a promising new platform technology in the design of novel drug delivery systems to improve drug performance.