Modified Rose Bengal assay for surface hydrophobicity evaluation of cationic solid lipid nanoparticles (cSLN).

Surface hydrophobicity of nanocarriers influences protein binding and subsequently fate of nanoparticles in blood circulation. Therefore, characterization of surface hydrophobicity of nanocarriers provides important preclinical information. Here, a modified classical adsorption method for the needs of characterization of cationic solid lipid nanoparticles (cSLN) was developed. We have identified possible method limitations that should be considered when performing the analysis, i.e. the problems associated with particle separation from the dispersion and their own absorbance in visible spectrum. We propose two modified methods for performing the assay overcoming the stated limitations. We also discuss here evaluation by different approaches (calculation of binding constants or partitioning quotient) and their suitability for the prepared cSLN formulation. Overall, we confirmed that our modified adsorption method can provide useful information about surface properties of (cationic) SLN, however, performing and evaluation of the assay need special attention in order to obtain the desired results.

Cationic solid lipid nanoparticles (cSLN): structure, stability and DNA binding capacity correlation studies.

Cationic solid lipid nanoparticles (cSLN) are promising lipid nanocarriers for intracellular gene delivery based on well-known and widely accepted materials. cSLN containing single-chained cationic lipid cetyltrimethylammonium bromide were produced by high pressure homogenization and characterized in terms of (a) particle size distribution by photon correlation spectroscopy (PCS) and laser diffractometry (LD), (b) thermal behaviour using differential scanning calorimetry (DSC) and (c) the presence of various polymorphic phases was confirmed by X-ray diffraction (WAXD). SLN composed of Imwitor 900P (IMW) showed different pDNA stability and binding capacity in comparison to those of Compritol 888 ATO (COM). IMW-SLN, having z-ave=138-157 nm and d(0.5)=0.15-0.158 µm could maintain this size for 14 days at room temperature. COM-SLN had z-ave=334 nm and d(0.5)=0.42 µm on the day of production and could maintain similar size during 90 days. IMW-SLN revealed improved pDNA binding capacity. We attempted to explain these differences by different interactions between the solid lipid and the tested cationic lipid.

SiRNA delivery: challenges and role of carrier systems.

Gene silencing by RNA interference is a rapidly growing therapeutic area for managing diseases. Despite research advances in this direction, the poor cellular uptake of synthetic small interfering RNAs is a major impediment to their clinical applications. Polymer and lipid-based systems are attractive carrier systems for delivery of siRNA and provide options for desirable engineering of carrier particles. In this review, there is a detailed discussion of RNAi delivery systems and recent advances in the field.

Nevirapine nanosuspensions for HIV reservoir targeting.

In this paper we discuss, production, characterization and in-vivo evaluation of nevirapine nanosuspensions. Laser diffraction showed that the average particles size was 457 nm. Following single-dose administration, the plasma gamma concentration profiles showed fast release. Macrophage uptake studies confirmed enhanced cellular uptake for nanonized nevirapine with no added cytotoxicity. Gamma scintigraphy showed that the nanosuspension prepared can be used to target spleen, thymus and lungs, which represent anatomical viral reservoirs. Thus nevirapine nanosuspensions with targeting potential have been prepared successfully.

Stavudine entrapped lipid nanoparticles for targeting lymphatic HIV reservoirs.

The main objective of present research study was to evaluate the potential of lipid nanoparticles for active delivery of an antiretroviral drug to lymphatic tissues. Stavudine entrapped drug loaded solid lipid nanoparticles (SLNs) were prepared and characterized for a variety of physicochemical parameters such as appearance, particle size, polydispersity index and zeta potential. The targeting potential of the prepared nanoparticles was investigated by carrying out ex vivo cellular uptake studies in macrophages which depicted several times enhanced uptake as compared to pure drug solution. Further, the lymphatic drug levels and organ distribution studies demonstrated efficiency of the developed nanoparticles for prolonged residence in spleenic tissues. Thus it was concluded that stavudine entrapped lipid carriers can be exploited for effective and targeted delivery to cellular and anatomical HIV reservoirs and may ultimately increase the therapeutic safety and reduce side effects.

Production & stability of stavudine solid lipid nanoparticles--from lab to industrial scale.

The production of stavudine-loaded solid lipid nanoparticles (SLN) for intravenous injection was scaled up from lab scale (40 g) to medium scale (10 kg) and large scale (20/60 kg). The SLN were produced by high pressure homogenization of stavudine lipid melt dispersed in hot surfactant solution (pre-emulsion) applying 800 bar pressure. Employed were piston-gap homogenizers with increasing capacity (APV Gaulin products LAB 40, LAB 60 and Gaulin 5.5, and Avestin C50), using them in the continuous (circulation) and discontinuous mode. Size analysis was performed by photon correlation spectroscopy (PCS), laser diffractometry and light microscopy. At lab scale a PCS size of 53 nm was obtained. At the same pressure, all homogenizers on larger scale yielded a size in the range of the lab scale product (35-70 nm). Differences were found in the size as a function of circulation time (size increase or size reduction with time) and the number of cycles required (1 or 5) for the optimal product. The stavudine SLN formulation (2% lipid content, high surfactant to lipid ratio) showed a different behavior to conventional higher concentrated SLN suspensions or nanoemulsions (10% or 20% lipid/oil, low surfactant to lipid ratio). In general, smallest sizes were obtained in the discontinuous mode after just one homogenization cycle. The continuous production mode was only efficient with a 10 kg batch size using the LAB 60. In addition, the long-term stability over 1 year was monitored at refrigeration, room temperature and at 40°C to assess a potential effect of the homogenizer type on stability. All batches at room temperature and below were stable, only a negligible increase in size was observed.

smartCrystal combination technology--scale up from lab to pilot scale and long term stability.

The production of nanocrystals was scaled up from lab scale (20 g) to pilot scale (3 kg), scale up factor 150. The flavonoid apigenin was used as model compound, with potential for pharma, cosmetic and nutraceutical products. Lab scale production was performed by high pressure homogenization (HPH), pilot scale by applying the smartCrystal combination technology (CT), combining pearl milling and a subsequent HPH (1 cycle, 300 bar). The obtained particle sizes were compared on the basis of photon correlation spectroscopy (PCS), laser diffractometry (LD) and light microscopy. The results showed, that assessment of successful scale up depends on the characterization method used, e.g., PCS covering only a part of the particle size range (3 nm-3 microm) of the population, or LD the full size distribution. Long-term stability was predicted on zeta potential (ZP) measurements. Lab and pilot scale possessed sufficiently high ZP values (> 30 mV) for a stable dispersion, but the ZP values were different (5-7 mV). This was explained by differences in the Stern/Nernst potential of the nanocrystals, potentially due to different levels in the crystals where they break in a high energy process (HPH) versus a low energy size reduction (pearl mill). Independent on the production method and batch size, the nanosuspensions proved to be physically stable for 6 months at storage temperatures 4 degrees C, room temperature and 40 degrees C.