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Objective: To prepare stable and easy to handle formulation of solid lipid nanoparticles (SLNs) by freeze-drying with or without cryoprotectants, as appropriate. Materials and methods: SLNs were freeze-dried without cryoprotectants or with cryoprotectants in quantities selected by freeze-thaw test (sucrose, glucose) or literature search (trehalose, maltose). Appearance, re-dispersability and size distribution of re-dispersed samples were evaluated. Results: SLN could be freeze-dried using 10% sucrose, trehalose or maltose. Trehalose was effective in protecting one of presented formulations that was already very stable on its own; its efficiency in protecting other two formulations was limited. Discussion: Our results are in line with various reports of successful freeze-drying of SLN, but considering the stability of original dispersions, no improvement was achieved. Conclusion: We confirmed that trehalose is among the most suitable cryoprotectant for SLN, however it did not improve shelf-life of the most stable formulation. [ABSTRACT FROM AUTHOR]

Highlights: [•] Polyhydroxy surfactants are suitable surfactants for the stabilization of SLN. [•] Their use leads to small sized and physically stable SLN. [•] Their use enables the production of “skin-friendly” SLN for dermal drug delivery. [•] Physico-chemical properties of surfactants strongly influence size/stability of SLN. [•] Alkyl chain lengths of lipid matrix of SLN and stabilizer should be similar. [ABSTRACT FROM AUTHOR]

Abstract: Solid lipid nanoparticles (SLN) were produced using a full range of poloxamer polymers and poloxamine 908 for stabilization. The protein adsorption pattern acquired on the surface of these particles after intravenous injection is the key factor determining the organ distribution. Two-dimensional polyacrylamide gel electrophoresis (2-DE) was employed for determination of particle interactions with human plasma proteins. The objective of this study was to investigate changes in the plasma protein adsorption patterns in the course of variation of the polymers stabilizing the SLN. Considerable differences in the protein adsorption with regard to preferential adsorbed proteins were detected for the different stabilizers. Possible correlations between the polyethylene oxide (PEO) chain length and the adsorption of various proteins (first of all apolipoproteins) are shown and discussed. Besides the study of protein adsorption patterns, the total protein mass adsorbed to the SLN was also evaluated using the bicinchoninic acid (BCA)-protein assay. The knowledge concerning the interactions of proteins and nanoparticles can be used for a rational development of particulate drug carriers. Based on the findings presented in this paper, we anticipate that the in vivo well-tolerable SLN are a promising site-specific drug delivery system for intravenous injection. [Copyright &y& Elsevier]

Plasma proteins enriched on the surface of drug-delivery-purpose nanoparticles are regarded as key factors for determination of in vivo organ distribution after intravenous injection. Polysorbate 80-coated polybutylcyanoacrylate (PBCA) nanoparticles, preferentially adsorbing apolipoprotein E (apoE) on their surface, have previously been considered to deliver various drugs to the brain. In the present study, in vivo well tolerable solid lipid nanoparticles (SLN) using different types of polysorbates as stabilizers were produced. The influence of the different surfactants on in vitro adsorption of human plasma proteins was investigated using two-dimensional polyacrylamide gel electrophoresis (2-DE). Possible correlations of different amounts of adsorbed apoE to the hydrophilic–lipophilic balance (HLB) of the polysorbates are shown and discussed. Apolipoprotein C-II, albumin and immunoglobulin G, which are also decisive plasma proteins with regard to site-specific drug delivery of intravenously injected carriers to the brain, are compared with regard to adsorption. Moreover, certain similarities to the plasma protein adsorption patterns of previously analysed brain-specific PBCA nanoparticles could be detected. Despite some differences in adsorption behavior of proteins on the surface of polysorbate-stabilized SLN and PBCA nanoparticles, we conclude that in both cases polysorbate 80 might have the highest potential to deliver drugs to the brain. [ABSTRACT FROM AUTHOR]

Effects on skin hydration and viscoelasticity are important criteria during the development of novel cosmetic formulations. This study focuses on the in vivo performance of a conventional o/w cream and of the same cream enriched with solid lipid nanoparticles (SLN). Influences on skin hydration and viscoelastic properties were investigated with validated devices (Corneometer® and Cutometer®). After an application period of 4 weeks, significant changes in skin hydration were detected for both formulations. The SLN-enriched cream was significantly more effective than the conventional cream (+24% for the cream and +31% for the SLN-cream). The viscoelastic parameters UF and UA/UF remained almost unchanged, which is attributed to the young age of the volunteers. At this stage, SLN represent a promising compound for hydrating new cosmetic formulations. [Copyright &y& Elsevier]

The plasma proteins adsorbing onto intravenously injected carriers are considered to be crucial factors determining the organ distribution. Plasma protein adsorption patterns were analyzed on solid lipid nanoparticles (SLN) stabilized with Tween 80 or stabilized with poloxamer 188. The binding patterns were determined by applying two different sample preparation methods, i.e. removal of the SLN from the plasma by (a) centrifugation and (b) gel filtration to assess, if the separation method has an effect on the patterns obtained. The Tween 80-modified SLN adsorbed the major plasma proteins known from particles with blood-brain barrier specificity. Poloxamer 188-surface modified SLN adsorbed the proteins known from model particles that exhibit prolonged circulation time in the blood. It is concluded that the biodegradable SLN stabilized with Tween 80 can potentially be used as drug carriers to the blood-brain barrier having a relatively long residence time in the blood stream. For the poloxamer 188-stabilized SLN a relatively long resistance time in the blood is predicted leading to potential accumulation in the bone marrow when looking at the distinct CII/CIII adsorption. [ABSTRACT FROM AUTHOR]

Solid lipid nanoparticles (SLN) are novel delivery systems for pharmaceutical and cosmetic active ingredients. This paper highlights advantages of SLN for cosmetic applications. The dependence of the occlusive effect on the particle size of SLN due to film formation is presented by in vitro data. An in vivo study showed that addition of 4% SLN to a conventional o/w cream lead to an increase of skin hydration of 31% after 4 weeks. The application of SLN as physical sunscreens and as active carriers for molecular sunscreens has also been investigated. The amount of molecular sunscreen could be decreased by 50% while maintaining the protection level compared to a conventional emulsion. [Copyright &y& Elsevier]

Abstract: Topical application of lutein as an innovative antioxidant, anti-stress and blue light filter, which is able to protect skin from photo damage, has got a special cosmetic and pharmaceutical interest in the last decade. Lutein is poorly soluble, and was therefore incorporated into nanocarriers for dermal delivery: solid lipid nanoparticles (SLN), nanostructured lipid carriers (NLC) and a nanoemulsion (NE). Nanocarriers were produced by high pressure homogenization. The mean particle size was in the range of about 150nm to maximum 350nm, it decreased with increasing oil content of the carriers. The zeta potential in water was in the range −40 to −63mV, being in agreement with the good short term stability at room temperature monitored for one month. In vitro release was studied using a membrane free model. Highest release in 24h was observed for the nanoemulsion (19.5%), lowest release (0.4%) for the SLN. Release profiles were biphasic (lipid nanoparticles) or triphasic (NE). In vitro penetration study with a cellulose membrane showed in agreement highest values for the NE (60% in 24h), distinctly lower values for the solid nanocarriers SLN and NLC (8–19%), lowest values for lutein powder (5%). Permeation studies with fresh pig ear skin showed that no (SLN, NLC) or very little lutein (0.4% after 24h) permeated, that means the active remains in the skin and is not systemically absorbed. The nanocarriers were able to protect lutein against UV degradation. In SLN, only 0.06% degradation was observed after irradiation with 10 MED (Minimal Erythema Dose), in NLC 6–8%, compared to 14% in the NE, and to 50% as lutein powder suspended in corn oil. Based on size, stability and release/permeation data, and considering the chemical protection of the lutein prior to its absorption into the skin, the lipid nanoparticles are potential dermal nanocarriers for lutein. [Copyright &y& Elsevier]

Cationic solid lipid nanoparticles (SLN) for gene transfer are formulated using the same cationic lipids as for liposomal transfection agents. To investigate the differences and similarities in structure and performance between SLN and liposomes, a SLN preparation (S1), its counterpart formulation without matrix lipid (L1), a commercially available liposomal preparation (DLTR) — all based on the cationic lipid DOTAP—and a liposomal formulation that additionally contained the helper lipid dioleoylphosphatidylethanolamine (DOPE) (Escort™) were compared. Photon correlation spectroscopy (PCS) showed that the SLN were smaller in diameter than the corresponding liposomes (88 vs. 148 nm) and atomic force microscopy (AFM) supported the expected structural differences. Desoxy ribonuclein acid (DNA) binding differed only marginally. Surprisingly, reporter gene expression was comparable between all DOTAP based formulations (S1, L1, DLTR), surpassed only by the DOPE containing liposomes (Escort™). In conclusion, cationic lipid composition seems to be more dominant for in vitro transfection performance than the kind of colloidal structure it is arranged in. Hence, cationic SLN extend the range of highly potent non-viral transfection agents by one with favourable and distinct technological properties. Further SLN optimisation should be facilitated by the accumulated knowledge about cationic lipids in liposomal formulations. [Copyright &y& Elsevier]

This investigation is focused on the enhancement of in vitro transfection activity by optimizing cationic lipid and matrix lipid composition of solid lipid nanoparticles (SLN). For this purpose SLN were formulated by using two different matrix lipids and six different cationic detergents. These 12 formulations were tested for physical parameters such as particle size, zeta potential and DNA-binding capacity, and also for their biological properties such as cytotoxicity and in vitro transfection efficiency. The SLN were produced by hot high-pressure homogenization, all formulations were physically stable and showed a highly positive surface charge (+34 to +45 mV). In vitro cytotoxicity measurements on COS-1 cells revealed that cytotoxicity is strongly dependent on the cationic lipid used. SLN made from one-tailed cationic detergents were highly cytotoxic. In contrast the two-tailed cationic lipids were all well tolerated. Transfection activity seems to be determined by both the cationic lipid and the matrix lipid used. Here, the combination of cetylpalmitate and N-[1-(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium chloride led to significantly higher transfection efficiencies than in all other tested combinations. These results indicate that well tolerated and highly efficient in vitro transfection could be achieved with SLN whenever selecting good combinations of two-tailed cationic lipids and matrix lipids. [Copyright &y& Elsevier]