Rheology of nanostructured lipid carriers (NLC) suspended in a viscoelastic medium.

Colloidal lipid nanoparticle dispersions have been characterized by rheological measurements using two different nanostructured lipid carrier (NLC)-based formulations intended for cosmetic application of substances like sunflower oil and alpha-tocopherol. This study has shown that rheological and viscoelastic properties of aqueous NLC dispersions are quantitatively very different depending on the composition of the oil phase and the temperature of storage despite similar or even identical particle size. NLC were loaded with 30% active ingredient relative to the particle mass. Stearyl alcohol was used as lipid matrix and the particle sizes determined by photon correlation spectroscopy were in the range 210-270 nm. In general, sun flower oil-loaded NLC dispersions showed distinctly higher storage modulus (G'), loss modulus (G") and complex viscosity (eta*). Storage at lower temperature (4 degrees C versus 20 degrees C) delay the build up of a microstructure affected not only by size and stabilizer but also loaded ingredient and storage history after preparation, i.e. storage at room temperature accelerates the build up of a final suspension structure.

A novel approach based on lipid nanoparticles (SLN) for topical delivery of alpha-lipoic acid.

This study describes the development, preparation and characterization of solid lipid nanoparticles (SLN) containing the novel anti-ageing substance alpha-lipoic acid. Lipoic acid is chemically labile, i.e. the degradation products possess an unpleasant odour. Therefore, the active was encapsulated in SLN. A lipid with low melting point (Softisan 601) was selected for preparation of active-loaded SLN after screening the solubility of alpha-lipoic acid in physicochemically different lipids. An entrapment efficiency of 90% (UV analysis) was obtained for all developed formulations using Miranol Ultra C32 as emulsifying agent. Particle size stability was monitored during 3 months storing the samples at 20 degrees C and at 4 degrees C. Results of DSC analysis confirm that these systems are characterized by a solid-like behaviour, although with a very low crystallinity index.

Medium scale production of solid lipid nanoparticles (SLN) by high pressure homogenization.

Solid lipid nanoparticles (SLN) were produced by high pressure homogenization using piston-gap homogenizers. Batch sizes varied between 40 ml and 50 l. Because of the different batch sizes, different homogenizer types were used, but the same functional principles were maintained, and the change from 40 ml to 50 l was not critical. With increasing batch sizes, the product quality in terms of particle size distribution and physical storage stability improved. Medium scale (30 l and 50 l) drug-free and drug-loaded SLN batches could be produced reproducibly and batch-to-batch uniformity was proven: within one batch particle sizes were homogeneous. This study revealed the influence of pressure and temperature for the hot homogenization technique A change of pressure between 300-500 bars induced only minor differences in particle size, but some influence of the heating temperature was found. More important than control of the heating process was the control of the cooling process of the final product. A too rapid cooling deteriorated the product quality: cooling with water of 18 degrees C proved to be the optimum cooling condition.

Production of solid lipid nanoparticles (SLN): scaling up feasibilities.

Solid lipid nanoparticles (SLN/Lipopearls) are widely discussed as a new colloidal drug carrier system. In contrast to polymeric systems, such as Polylactic copolyol microcapsules, these systems show with a good biocompatibility, if applied parenterally. The solid lipid matrices can be comprised of fats or waxes, and allow protection of incorporated active ingredients against chemical and physical degradation. The SLN can either be produced by 'hot homogenization' of melted lipids at elevated temperatures or by a 'cold homogenization' process. This paper deals with production technologies for SLN formulations, based on non-ethoxylated fat components for topical application and high pressure homogenization. Based on the chosen fat components, a novel and easy manufacturing and scaling-up method was developed to maintain chemical and physical integrity of the encapsulated active ingredients in the carrier.

Encapsulation of retinoids in solid lipid nanoparticles (SLN).

SLN have been suggested for a broad range of applications, such as intravenous injection, peroral, or dermal administration. The incorporation of the drug in the core of the SLN has to be ensured for these applications, but the inclusion of drugs in SLN is poorly understood. This study is a contribution to further describe the inclusion properties of colloidal lipids and to propose incorporation mechanisms. Besides the well known methods to investigate entrapment of actives in nanoparticles such as DSC or microscopy, the present study focussed on yet a different approach. Based on the different chemical stability of retinoids in water and in a lipid phase, a method to derive information on the distribution of the drug between SLN-lipid and the water phase was established. Comparing different lipids, glyceryl behenate gave superior entrapment compared to tripalmitate, cetyl palmitate and solid paraffin. Comparing three different drugs, entrapment increased with decreasing polarity of the molecule (tretinoin < retinol < retinyl palmitate). The encapsulation efficacy was successfully enhanced by formulating SLN from mixtures of liquid and solid lipids. These particles were solid and provided better protection of the sensitive drugs than an emulsion. X-ray investigations revealed that good encapsulation correlated with a low degree of crystallinity and lattice defects. With highly ordered crystals, as in the case of cetyl palmitate, drug expulsion from the carrier was more pronounced.

Scaling up feasibility of the production of solid lipid nanoparticles (SLN).

Solid lipid nanoparticles (SLN/Lipopearls) are widely discussed as colloidal drug carrier system. In contrast to polymeric systems, such as polylactic copolyol capsules, these systems show up with a good biocompatibility, if applied parenterally. The solid lipid matrices can be comprised of fats or waxes and allow protection of incorporated active ingredients against chemical and physical degradation. The SLN can either be produced by "hot homogenisation" of melted lipids at elevated temperatures or a "cold homogenization" process. This paper deals with production technologies for SLN formulations, based on non-ethoxylated fat components for topical application and high pressure homogenization (APV Deutschland GmbH, D-Lübeck). Based on the chosen fat components, a novel and easy manufacturing and scaling up method was developed to maintain chemical and physical integrity of encapsulated active and carrier.

Solid lipid nanoparticles (SLN) based on binary mixtures of liquid and solid lipids: a (1)H-NMR study.

SLN with improved payloads and enhanced storage stability were investigated. Based on the experiences with solid lipid nanoparticles, a new type of solid lipid nanoparticle has been developed by incorporating triglyceride containing oils in the solid shell of the particle. The structure and mixing behaviour of these particles was characterised by DSC and (1)H-NMR. DSC yields information on the melting and crystallisation behaviour of the solid and liquid constituents of the particles. NMR is especially suited for the characterisation of the liquid oil domains inside the SLN. In this study a medium chain triglyceride oil was successfully incorporated in a matrix of a solid long chain glyceride (glyceryl behenate). The resulting particles were solid but the oil inside the particle remained in a liquid state. The relation between oil supplementation and melting point depression of glyceryl behenate proved to be linear. Mobility of the oil molecules inside the particles was considerably reduced compared to the emulsified oil. Moreover, two different chemical shifts for each of the lipid signals were observed indicating two different chemical environments. The experimental data is in line with a model describing uniform distribution of the oil molecules in the glyceryl behenate for low oil loads. However, at higher oil loads our data indicate the formation of oil clusters within the solid nanoparticle.

Solid lipid nanoparticles (SLN) for controlled drug delivery - a review of the state of the art.

Solid lipid nanoparticles (SLN) introduced in 1991 represent an alternative carrier system to traditional colloidal carriers, such as emulsions, liposomes and polymeric micro- and nanoparticles. SLN combine advantages of the traditional systems but avoid some of their major disadvantages. This paper reviews the present state of the art regarding production techniques for SLN, drug incorporation, loading capacity and drug release, especially focusing on drug release mechanisms. Relevant issues for the introduction of SLN to the pharmaceutical market, such as status of excipients, toxicity/tolerability aspects and sterilization and long-term stability including industrial large scale production are also discussed. The potential of SLN to be exploited for the different administration routes is highlighted. References of the most relevant literature published by various research groups around the world are provided.

Vitamin A loaded solid lipid nanoparticles for topical use: occlusive properties and drug targeting to the upper skin.

To evaluate the potential use of solid lipid nanoparticles (SLN) in dermatology and cosmetics, glyceryl behenate SLN loaded with vitamin A (retinol and retinyl palmitate) and incorporated in a hydrogel and o/w-cream were tested with respect to their influence on drug penetration into porcine skin. Conventional formulations served for comparison. Excised full thickness skin was mounted in Franz diffusion cells and the formulations were applied for 6 and 24 h, respectively. Vitamin A concentrations in the skin tissue suggested a certain drug localizing effect. High retinol concentrations were found in the upper skin layers following SLN preparations, whereas the deeper regions showed only very low vitamin A levels. Because of a polymorphic transition of the lipid carrier with subsequent drug expulsion following the application to the skin, the drug localizing action appears to be limited for 6-24 h. Best results were obtained with retinol SLN incorporated in the oil-in-water (o/w) cream retarding drug expulsion. The penetration of the occlusion sensitive drug retinyl palmitate was even more influenced by SLN incorporation. Transepidermal water loss (TEWL) and the influence of drug free SLN on retinyl palmitate uptake exclude pronounced occlusive effects. Therefore enhanced retinyl palmitate uptake should derive from specific SLN effects and is not due to non-specific occlusive properties.

Characterisation of a novel solid lipid nanoparticle carrier system based on binary mixtures of liquid and solid lipids.

A drug carrier of colloidal lipid particles with improved payloads and enhanced storage stability was investigated. Based on the experiences with hard fats nanoparticles, a new type of solid lipid nanoparticles (SLN) has been developed by incorporating triglyceride containing oils in the solid core of said particle. The structure and mixing behaviour of these particles were characterised and practical implications on controlled release properties tested. Nanoparticles were characterised by their melting and recrystallisation behaviour as recorded by differential scanning calorimetry (DSC). Polymorphic form and bilayer arrangement were assigned by wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS). Size distribution and storage stability were investigated by laser diffractometry (LD). Release properties were studied by drug release model according to Franz. A medium chain triglyceride oil was incorporated successfully in a matrix of a solid long chain glyceride. The crystal order was greatly disturbed, however, the carrier remained solid. The oil inside the particle remained in a liquid state and induced a slight shift form the beta' polymorph to the beta(i) form. Long spacings varied within 0.1 nm with increasing oil loads. Nanoparticles with low oil concentrations showed sustained release properties. Improved drug load levels were encapsulated by lipid particles supplemented with oily constituents. Thus, the presented carrier adds additional benefits to the well-known opportunities of conventional SLN and is suited for topical use.

Vitamin A-loaded solid lipid nanoparticles for topical use: drug release properties.

Burst release as well as sustained release has been reported for SLN suspensions. For dermal application, both features are of interest. Burst release can be useful to improve the penetration of a drug. Sustained release becomes important with active ingredients that are irritating at high concentrations or to supply the skin over a prolonged period of time with a drug. Glyceryl behenate SLN were loaded with vitamin A and the release profiles were studied. Franz diffusion cells were used to assess the release kinetic over a period of 24 h. Within the first 6 h retinol SLN displayed controlled release. After longer periods (12-24 h) the release rate increased and even exceeded the release rate of comparable nanoemulsions. Pure SLN dispersions are characterised by low viscosity. In contrast to membranous vesicles, SLN can also be stably incorporated in convenient topical dosage forms like hydrogels or creams. In the Franz diffusion cell these preparations showed a controlled release over 12-18 h. Similar to SLN dispersions an increase in release rate over a 24-h period was found. A good correlation between polymorphic transitions and increased drug release was observed in this study. Sustained release was often related to the metastable beta' polymorph. Drug expulsion is explained by a reduction of amorphous regions in the carrier lattice due to a beta'-->beta(i) polymorphic transition. This transformation can be controlled with surfactant mixtures or, in the case of the hydrogel and oil/water cream, with humectants or gelling agents. Thus, the release rate for the topical route of application is adjustable.

Comparison of wax and glyceride solid lipid nanoparticles (SLN).

The present study compares solid lipid nanoparticles (SLN) formulated with either wax or glyceride bulk material. While most published data deal with glyceride SLN, little knowledge is reported on wax carriers. The two types were compared with respect to drug encapsulation efficacy, particle size distribution after production and storage, and crystal packing. The inclusion of retinol as a model drug was investigated. Retinol is chemically unstable in water and rather stable in lipid phases. Thus, rapid degradation of retinol indicates rapid drug expulsion from the carrier. Good stability indicates an effective drug encapsulation in the lipid phase of the nanoparticles. Particle size distribution was measured by laser diffractometry. Subcell packing and assignment of polymorphic forms was investigated by WAXS measurements. Glyceride SLN showed good drug encapsulation, while physical stability was poor. In contrast, wax SLN possessed good physical stability but lacked sufficient drug encapsulation in the solidified state. These differences were attributed in part to different crystal packing. Less ordered crystal lattices favour successful drug inclusion, as in the case of glyceryl monosterate and glyceryl behenate SLN. The highly ordered crystal packing of wax SLN comprised of beeswax or cetyl palmitate, for instance, leads to drug expulsion, but also to superior physical stability.

Solid lipid nanoparticles (SLN/Lipopearls)--a pharmaceutical and cosmetic carrier for the application of vitamin E in dermal products.

Solid lipid nanoparticles (SLN, Lipopearls) are nanoparticles made from solid lipids by high pressure homogenization. Incorporation of chemically labile active ingredients into the solid lipid matrix protects against chemical degradation, which is shown for vitamin E. The SLN are physically stable in aqueous dispersions and also after incorporation into a dermal cream as proven by photon correlation spectroscopy and differential scanning calorimetry. Electron microscopy and atomic force microscopy data reveal the spherical shape of the SLN and the detailed structure of the particle surface. Ultrafine particles form an adhesive film leading to an occlusive effect on the skin. The occlusion promotes the penetration of vitamin E into the skin, as shown by the stripping test. In addition to chemical stabilization of active ingredients, occlusive effects on the skin and subsequent enhanced penetration of compounds, the SLN also possess a pigment effect covering undesired colours leading to an increased aesthetic acceptance by the customer.

Coenzyme Q10, a cutaneous antioxidant and energizer.

The processes of aging and photoaging are associated with an increase in cellular oxidation. This may be in part due to a decline in the levels of the endogenous cellular antioxidant coenzyme Q10 (ubiquinone, CoQ10). Therefore, we have investigated whether topical application of CoQ10 has the beneficial effect of preventing photoaging. We were able to demonstrate that CoQ10 penetrated into the viable layers of the epidermis and reduce the level of oxidation measured by weak photon emission. Furthermore, a reduction in wrinkle depth following CoQ10 application was also shown. CoQ10 was determined to be effective against UVA mediated oxidative stress in human keratinocytes in terms of thiol depletion, activation of specific phosphotyrosine kinases and prevention of oxidative DNA damage. CoQ10 was also able to significantly suppress the expression of collagenase in human dermal fibroblasts following UVA irradiation. These results indicate that CoQ10 has the efficacy to prevent many of the detrimental effects of photoaging.

Mitogenic activity of high molecular polysaccharide fractions isolated from the cuppressaceae Thuja occidentalis L. enhanced cytokine-production by thyapolysaccharide, g-fraction (TPSg).

Thuja polysaccharide g fraction (TPSg) was shown to be an inducer of the CD4+ fraction of the human peripheral blood T-cell subset (1,2). Furthermore, it could be demonstrated that TPSg is a potent inhibitor of the expression of HIV-1-specific antigens and of the HIV-1-specific reverse transcriptase (3). This report deals with the cytokine pattern induced by TPSg in human peripheral blood lymphocyte (PBL) and purified monocyte/macrophage cultures. In addition, a further characterization of the CD4+ T-cell fraction stimulated by TPSg was performed by FACS analysis. TPSg is induces IL-1 beta, IL-2, IL-3, IL-6, gamma-IFN, G-CSF, GM-CSF, and TNF-beta production in PBL cultures; and IL-1 beta and IL-6 in monocyte/macrophage cultures. Enzyme-linked immunosorbent assays (ELISAs) demonstrated that no IL-4 was produced by PBL cultures under TPSg influence.

Mitogenic activity of high molecular polysaccharide fractions isolated from the Cupressaceae Thuja occidentale L. I. Macrophage-dependent induction of CD-4-positive T-helper (Th+) lymphocytes.

The arborvitae or Thuja occidentale L., one of the Cupressaceae, has rarely been investigated until now. Several authors have demonstrated that allopathic extracts of this plant could be used as strong antiviral agents directed against plant and animal viruses. Polysaccharide fractions with molecular weights ranging between 20,000 and 1,000,000 and higher have been isolated from the aqueous alkaline extract of the herbal parts of T. occidentale L. by ethanol precipitation and fractionation by ultrafiltration. High molecular subfractions of Thujapolysaccharides (TPS) proved to be highly mitogenic on peripheral blood leukocytes. It was demonstrated by the alcalic immune phosphatase-antiphosphatase and Pappenheim staining methods that the mitogenic and cluster-forming activity of TPS cause T cell induction, in particular, of CD 4-positive T-helper/inducer cells as opposed to B cells. The CD-4+ T-helper/inducer cell induction is connected to an increased production of IL-2. The cluster-forming ability and mitogenity of TPS correlates well with the 3H-thymidine uptake and seems to be IL-1 and IFN-gamma dependent as could be shown by blocking the mitogenic effect using anti-IL-1- and anti-IFN antibodies. Whether it is possible to use these polysaccharide fractions as an adjuvant in the therapy of immune deficiency syndromes and cancer must now be further investigated.