Physicochemical properties of nevirapine-loaded solid lipid nanoparticles and nanostructured lipid carriers

Solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs) coated with human serum albumin (HSA) were fabricated for formulating nevirapine (NVP). Here, NLCs contained low-melting-point oleic acid (OA) in the internal lipid phase. The results revealed that the two nanoparticles were uniformly distributed with the average diameter ranging from 145 to 180 nm. The surface HSA neutralized the positive charge of dimethyldioctadecyl ammonium bromide (DODAB) on SLNs and NLCs and reduced their zeta potential. In a fixed ratio of solid lipids, SLNs entrapped more NVP than NLCs. The incorporation of OA also reduced the thermal resistance of NLCs and accelerated the release of NVP from the nanocarriers. When incubated with DODAB-stabilized SLNs, the viability of human brain-microvascular endothelial cells (HBMECs) reduced. However, the surface HSA increased the viability of HBMECs about 10% when the concentration of SLNs was higher than 0.8 mg/mL. HSA-grafted SLNs and NLCs can be effective formulations in the delivery of NVP for viral therapy.     

Physicochemical characterization of nanotemplate engineered solid lipid nanoparticles

As the physicochemical characteristics of solid lipid nanoparticles (SLNs) play a critical role in their success, it is important to understand how the materials and process used in their preparation affect these properties. In this study, two stearyl alcohol-based formulations were prepared using nanotemplate engineering technology and characterized. Both formulations were of a small particle size (<100 nm), ellipsoidal shape, and low polydispersity. (1)H NMR spectroscopy confirmed that the SLNs have the expected solid core structure and PEGylated surface. Analysis of the bulk materials indicated that a number of complex interactions are present among the SLN components, including a eutectic between stearyl alcohol and Brij 78. The decreased crystallinity resulting from these interactions may allow for enhanced drug loading. Physiological stability was identified and confirmed as a potential problem due to the low melting point of the eutectic. However, it is expected that with appropriate formulation modifications nanotemplate engineered SLNs will possess the properties necessary for a successful drug delivery system.     

Thermal characterization of solid lipid nanoparticles containing praziquantel

Solid lipid nanoparticles (SLNs), loaded and unloaded with praziquantel (PRZ-load SLN and PRZ-unload SLN) were prepared by two different procedures: (a) oil-in-water hot microemulsion method, obtaining at 70 °C an optically transparent blend composed of surfactant, co-surfactant, and water; and (b) oil-in-water microemulsion method, dissolving the lipid in an immiscible organic solvent, emulsified in water containing surfactants and co-surfactant, and then evaporated under reduced pressure at 50 °C. The mean diameter, polydispersity index (PdI), and zeta potential were 187 to 665 nm, 0.300 to 0.655, and −25 to −28 mV respectively, depending on the preparation method. The components, binary mixture, SLNs loaded and unloaded with PRZ, and physical mixture were evaluated by differential scanning calorimetry (DSC) and thermogravimetry (TG). The non-isothermal isoconversional Flynn-Wall–Ozawa method was used to determine the kinetic parameters associated with the thermal decomposition of the samples. The experimental data indicated a linear relationship between the apparent activation energy E and the pre-exponential factor A, also called the kinetic compensation effect (KCE), allowing us to determine the stability with respect to the preparation method. Loading with PRZ increased the thermal stability of the SLNs.     

Cholesterylbutyrate solid lipid nanoparticles as a butyric acid prodrug

Cholesterylbutyrate (Chol-but) was chosen as a prodrug of butyric acid. Butyrate is not often used in vivo because its half-life is very short and therefore too large amounts of the drug would be necessary for its efficacy. In the last few years butyric acid's anti-inflammatory properties and its inhibitory activity towards histone deacetylases have been widely studied, mainly in vitro. Solid Lipid Nanoparticles (SLNs), whose lipid matrix is Chol-but, were prepared to evaluate the delivery system of Chol-but as a prodrug and to test its efficacy in vitro and in vivo. Chol-but SLNs were prepared using the microemulsion method; their average diameter is on the order of 100-150 nm and their shape is spherical. The antineoplastic effects of Chol-but SLNs were assessed in vitro on different cancer cell lines and in vivo on a rat intracerebral glioma model. The anti-inflammatory activity was evaluated on adhesion of polymorphonuclear cells to vascular endothelial cells. In the review we will present data on Chol-but SLNs in vitro and in vivo experiments, discussing the possible utilisation of nanoparticles for the delivery of prodrugs for neoplastic and chronic inflammatory diseases.     

Antitumor activity and pharmacokinetics of podophyllotoxin incorporated into solid lipid nanoparticles

To evaluate the antitumor activity and pharmacokinetics of podophyllotoxin (PPT) incorporated into solid lipid nanoparticles (SLN), Kunming mice inoculated with flesh tumor were used as animal model. The mice received a single daily intraperitoneal injection of PPT in 20% ethanol (5 mg/kg) and PPT-SLN (5 mg/kg in PPT) for 3 weeks. Gross tumor volumes, body weight and clinical observations were recorded daily. The mice were sacrificed for 24 h after the last administration, and the tumor inhibition rate was calculated with the tumor weight. For the pharmacokinetics research, the mice were treated with intraperitoneal injection of PPT (10 mg/kg) and PPT-SLN (10 mg/kg in PPT). Blood samples were collected at different time to determine the PPT concentration in plasma by HPLC. Blood drug level-time curve was made and pharmacokinetic parameters were calculated. As a result of drug administration, the tumor volume and weight of the mice injected with PPT-SLN were significantly restrained compared with mice treated with PPT or negative control. The tumor inhibition rate of 58.13% showed a significant antitumor activity of PPT-SLN. At the same time, the increased weight gain of the mice injected with PPT-SLN suggested a reduced toxicity of PPT in SLN. Pharmacokinetics study displayed a higher blood concentration, a prolonged circulation time, and an increased bioavailability of PPT-SLN compared with those of PPT. Our results demonstrated that PPT-SLN could optimize pharmacokinetics, enhance antitumor activity and attenuate toxicity, so it has a promising prospect for the application in anti-tumor treatment. Supported by the National Natural Science Foundation of China (Grant No. 50673078), the Innovation Program of Shanghai Municipal Education Commission (Grant No. 08ZZ21) and the Shanghai Key Fundamental Project (Grant No. 07DZ19603)     

An easy and effective method for radiolabelling of solid lipid nanoparticles

Nanoparticle biodistribution study is of great importance in bringing nanomedicine to patients. In this article, solid lipid nanoparticle (SLN) with dimension less than 100 nm was successfully radiolabelled with ^99mTc by using sodium borohydride as a reducing agent (instead of stannous salts). Paclitaxel (PTX) was used as a model anticancer drug for the preparation of drug loaded SLN (PSLN). PSLN was characterized by standard methods. Encapsulation efficiency for PTX in PSLN was estimated by HPLC. PTX (Taxol formulation) and PSLN were radiolabelled separately and subsequent characterizations of these complexes were performed. Greater than 95 % radiolabelling efficiency was achieved and the labelling efficiency was calculated to be more than 90 % upto 24 h. Both the above-mentioned complexes passed the in vitro stability tests. PSLN achieved more brain concentration than Taxol as determined by biodistribution studies. This type of radiolabelling technique can be useful in preclinical evaluation of drug loaded SLN.     

Characterization of silver sulfadiazine-loaded solid lipid nanoparticles by thermal analysis

The aim of this study is the solid-state characterization of solid lipid nanoparticles (SLN) based on Compritol^® 888 (C888) and Lutrol^® F68 (F68), loaded with silver sulfadiazine (AgSD), used to develop sponge-like dressings to treat chronic skin ulcers such as decubitis and leg ulcers. Silver compounds like AgSD, in fact, are used to prevent and/or to treat wound colonization that could impair healing, also in the case of antibiotic-resistant bacteria. Thermal analysis, with support from powder X-ray diffractometry and Fourier transform infrared spectroscopy, is used to characterize lipid and drug bulk, unloaded and drug-loaded SLN. In particular, differential scanning calorimetry is used to investigate the degree of crystallinity and the solid-state modification of lipid, two parameters correlated to drug incorporation and drug release rates. The solid-state characterization demonstrates AgSD entrapment in C888 as a core enclosed into F68 shell. AgSD SLN are also stored at different temperatures 25 and 37 °C, respectively, to study the effect of storage conditions, that induce an increase of the lipid crystallinity index correlated to drug release from the lipid matrix.     

Loading of praziquantel in the crystal lattice of solid lipid nanoparticles

Praziquantel (PZQ) is the drug of choice for oral treatment of schistosomiasis and other fluke infections that affect humans. Its low oral bioavailability demands the development of innovative strategies to overcome the first pass metabolism. In this article, solid lipid nanoparticles loaded with PZQ (PZQ-SLN) were prepared by a modified oil-in-water microemulsion method selecting stearic acid as lipid phase after solubility screening studies. The mean particle size (Z-Ave) and zeta potential (ZP) were 500 nm and −34.0 mV, respectively. Morphology and shape of PZQ-SLN were analysed by scanning electron microscopy revealing the presence of spherical particles with smooth surface. Differential scanning calorimetry suggested that SLN comprised a less ordered arrangement of crystals and the drug was molecularly dispersed in the lipid matrix. No supercooled melts were detected. The entrapment efficiency (EE) and loading capacity of PZQ, determined by high performance liquid chromatography, were 99.06 ± 0.3 and 17.48 ± 0.05, respectively. Effective incorporation of PZQ into the particles was confirmed by small angle X-ray scattering revealing the presence of a lipid lamellar structure. Stability parameters of PZQ-SLN stored at room temperature (25 °C) and at 4 °C were checked by analysing Z-Ave, ZP and the EE for a period of 60 days. Results showed a relatively long-term physical stability after storage at 4 °C, without drug expulsion.     

Alternative sample preparation prior to two-dimensional electrophoresis protein analysis on solid lipid nanoparticles

The proteins adsorbing onto the surface of intravenously injected drug carriers are regarded as a key factor determining the organ distribution. Depending on the particle surface properties, certain proteins will be preferentially adsorbed, leading to the adherence of the particle to cells with the appropriate receptor. Therefore, the knowledge of the protein adsorption pattern and the correlation to in vivo behavior opens the perspective for the development of intravenous colloidal carriers for drug targeting. After incubation in plasma, the adsorbed proteins were analyzed using two-dimensional polyacrylamide gel electrophoresesis (2-D PAGE, 2-DE). The purpose of the present study was to develop an alternative separation method to separate solid lipid nanoparticles (SLN) carriers from plasma by gel filtration prior to 2-D PAGE. Via the specific absorption coefficients and a two-equation system, elution fractions were identified being practically plasma-free. This allows protein analysis on SLN which are typically in density too close to the density value of water to be separated by the standard centrifugation method. The SLN used for establishing the gel filtration were prepared in a way that they had a sufficiently low density to be additionally separated by centrifugation. The adsorption patterns obtained after separation with both methods were qualitatively and quantitatively identical, showing the suitability of the gel filtration.     

Substrate effects on interactions of lipid bilayer assemblies with bound nanoparticles

Understanding the interactions of nanoparticles with lipid membranes is crucial in establishing the mechanisms that govern assembly of membrane-based nanocomposites, nanotoxicology, and biomimetic inspired self-assembly. In this study, we explore binding of charged nanoparticles to lipid bilayers, both as liposomes and substrate supported assemblies. We find that the presence of a solid-support, regardless of curvature, eliminates the ability of zwitterionic fluid phase lipids to bind charged nanoparticles.     

Formulation design, preparation and physicochemical characterizations of solid lipid nanoparticles containing a hydrophobic drug: effects of process variables

This study aimed to prepare solid lipid nanoparticles (SLNs) of a hydrophobic drug, tretinoin, by emulsification-ultrasonication method. Solubility of tretinoin in the solid lipids was examined. Effects of process variables were investigated on particle size, polydispersity index (PI), zeta potential (ZP), drug encapsulation efficiency (EE), and drug loading (L) of the SLNs. Shape and surface morphology of the SLNs were investigated by cryogenic field emission scanning electron microscopy (cryo-FESEM). Complete encapsulation of drug in the nanoparticles was checked by cross-polarized light microscopy and differential scanning calorimetry (DSC). Crystallinity of the formulation was analyzed by DSC and powder X-ray diffraction (PXRD). In addition, drug release and stability studies were also performed. The results indicated that 10mg tretinoin was soluble in 0.45±0.07 g Precirol? ATO5 and 0.36±0.06 g Compritol? 888ATO, respectively. Process variables exhibited significant influence in producing SLNs. SLNs with <120 nm size, <0.2 PI, >I30I mV ZP, >75% EE, and ～0.8% L can be produced following the appropriate formulation conditions. Cryo-FESEM study showed spherical particles with smooth surface. Cross-polarized light microscopy study revealed that drug crystals in the external aqueous phase were absent when the SLNs were prepared at ≤0.05% drug concentration. DSC and PXRD studies indicated complete drug encapsulation within the nanoparticle matrix as amorphous form. The drug release study demonstrated sustained/prolonged drug release from the SLNs. Furthermore, tretinoin-loaded SLNs were stable for 3 months at 4°C. Hence, the developed SLNs can be used as drug carrier for sustained/prolonged drug release and/or to improve oral absorption/bioavailability.     

Surface modification of resorcinarene based self-assembled solid lipid nanoparticles for drug targeting

Prolyl-bearing amphiphilic resorcinarenes, e.g. tetrakis(N-methylprolyl)tetraundecylcalix[4]resorcinarene, self-assemble as stable solid lipid nanoparticles; these fully characterized systems could be further functionalized at their surface with proteins, and interact with specific antibodies bound on a sensor surface.     

The size of solid lipid nanoparticles: an interpretation from experimental design

This study aimed to investigate the role of different factors affecting the size of solid lipid nanoparticles (SLN), prepared by the emulsification-solvent evaporation method. A double factorial design was conducted so as to cover a wide range of sizes, highlighting zones with different behaviour with respect to changes in the controlled variables: lipid concentration, solvent:lipid ratio and emulsifier concentration. The solvent:lipid ratio constituted the main factor influencing particle size. Increasing the amount of solvent induced a decrease in the size. This was a general trend, essentially independent from solvent and lipid type. The amount of emulsifier had a non-trivial impact on size, depending on whether systems were located below, above or close to the optimal surface coverage. The amount of lipid had a limited influence upon particle size, being more relevant for lower lipid concentrations. An optimal formulation was selected for intermediate levels of the three variables. Sonication reduced both particle size and polydispersity. These particles were also tested as drug carriers using simvastatin as a model of lipophilic drug. SLN were able to entrap a high amount of simvastatin, with little effect upon size and zeta potential, constituting a promising carrier for lipophilic drugs.     

Effect of PLGA as a polymeric emulsifier on preparation of hydrophilic protein-loaded solid lipid nanoparticles

Most proteins are hydrophilic and poorly encapsulated into the hydrophobic matrix of solid lipid nanoparticles (SLN). To solve this problem, poly (lactic-co-glycolic acid) (PLGA) was utilized as a lipophilic polymeric emulsifier to prepare hydrophilic protein-loaded SLN by w/o/w double emulsion and solvent evaporation techniques. Hydrogenated castor oil (HCO) was used as a lipid matrix and bovine serum albumin (BSA), lysozyme and insulin were used as model proteins to investigate the effect of PLGA on the formulation of the SLN. The results showed that PLGA was essential for the primary w/o emulsification. In addition, the stability of the w/o emulsion, the encapsulation efficiency and loading capacity of the nanoparticles were enhanced with the increase of PLGA concentration. Furthermore, increasing PLGA concentration decreased zeta potential significantly but had no influence on particle size of the SLN. In vitro release study showed that PLGA significantly affected the initial burst release, i.e. the higher the content of PLGA, the lower the burst release. The released proteins maintained their integrity and bioactivity as confirmed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and biological assay. These results demonstrated that PLGA was an effective emulsifier for the preparation of hydrophilic protein-loaded SLN.     

Impact of arginine-modified solid lipid nanoparticles on the membrane charge of human brain-microvascular endothelial cells

Electrokinetic and electrostatic properties of human brain-microvascular endothelial cells (HBMECs) with the uptake of l-arginine (Arg)-modified solid lipid nanoparticles (RSLNs) were investigated. The exposure of these HBMECs to radiofrequency electromagnetic field (EMF) was also considered. As compared with the original culture of HBMECs, the uptake of the biomimetic RSLNs induced smaller absolute values of electrophoretic mobility, zeta potential, Donnan potential, and fixed charge density. In addition, an increase in the coverage fraction of Arg on the external layers of the RSLNs reduced the electrical characteristics of HBMECs. An increase in the power of EMF also decreased the charge of RSLNs-incorporating HBMECs. On the contrary, softness of HBMECs was enhanced by an increased coverage fraction of Arg and an increased power of EMF. Electrophysiology of HBMECs can be efficiently mediated by the novel RSLNs and exposure to EMF through fluctuation and redistribution of the membrane charge.     

Formulation and pharmacokinetic evaluation of tetracycline-loaded solid lipid nanoparticles for subcutaneous injection in mice

The aim of this work was to prepare tetracycline-loaded solid lipid nanoparticles (Tet-SLN), and to evaluate the potential of these colloidal carriers for subcutaneous injection. Tet-SLN was prepared by microemulsion method and the preparation conditions were optimized by ternary phase diagram. At optimized process conditions, lyophilized Tet-SLN showed spherical particles with a mean diameter of 87.2±46.9 nm and a negative zeta potential of -6.69 mV, up to 1.7% tetracycline drug content was achieved after loading. In vitro release test showed a biphasic release profile for Tet-SLN and more than 80% of the drug was liberated from Tet-SLN in 48 h. After subcutaneous injection of Tet-SLN to mice, a considerable sustained release was observed; tetracycline in blood could be detected lasting 36 h, and lower concentrations of tetracycline in all tissues tested compared to the free tetracycline solution were observed. In conclusion, Tet-SLN can be prepared well by microemulsion method and subcutaneous injection of SLN provide a new perspective for drug sustained release.     

Studies on crystallinity state of puerarin loaded solid lipid nanoparticles prepared by double emulsion method

In this work, solid lipid nanoparticles (SLN) have been prepared from water-in-oil-in-water double emulsion, using monocaprate as solid lipid, sorbitan monooleate (Span 80) and polyoxyethylene sorbitan monolaurate (Tween 20) as emulsifier, and puerarin as target drug. The morphology of SLN with drug loaded or not was investigated by the transmission electron microscope (TEM). The crystal order and structure of particles were studied by differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD), respectively. The results indicate that the diameters of SLN with puerarin inside are larger than those without drugs. The analysis of WAXD and DSC shows that the state of crystallinity SLN prepared by double emulsion method was worse than that of SLN prepared by microemulsion. And also the drug-loaded SLN presents a less ordered crystallinity than the drug-free SLN. But both the drug-free and drug-loaded SLN exist in an amorphous state. The reasons of the phenomenon have been discussed.     

Thermal characterization and compatibility studies of itraconazole and excipients for development of solid lipid nanoparticles

The current study was performed to investigate possible interactions between triazole antifungal drug itraconazole (ITR) with selected excipients commonly used for development of solid lipid nanoparticles. The excipients included common lipids (glyceryl behenate (Compritol 888 ATO?), glyceryl monostearate, stearic acid, and cetyl palmitate), charge inducers (dicetyl phosphate and stearlyamine), and surfactants (sodium cholate and sodium deoxycholate). Differential scanning calorimetry, isothermal stress testing, Fourier transform infrared spectral analysis, optical microcopy, and X-ray powder diffraction analysis were performed for assessing the compatibility between the drug and the excipients. Results of the study suggest that the stearic acid exhibited drug–excipient interactions, whereas all other excipients used in the study were found to be compatible with ITR.     

Temperature scanning ultrasonic velocity study of complex thermal transformations in solid lipid nanoparticles

The purpose of this study was to determine whether temperature scanning ultrasonic velocity measurements could be used to monitor the complex thermal transitions that occur during the crystallization and melting of triglyceride solid lipid nanoparticles (SLNs). Ultrasonic velocity ( u) measurements were compared with differential scanning calorimetry (DSC) measurements on tripalmitin emulsions that were cooled (from 75 to 5 degrees C) and then heated (from 5 to 75 degrees C) at 0.3 degrees C min (-1). There was an excellent correspondence between the thermal transitions observed in deltaDelta u/delta T versus temperature curves determined by ultrasound and heat flow versus temperature curves determined by DSC. In particular, both techniques were sensitive to the complex melting behavior of the solidified tripalmitin, which was attributed to the dependence of the melting point of the SLNs on particle size. These studies suggest that temperature scanning ultrasonic velocity measurements may prove to be a useful alternative to conventional DSC techniques for monitoring phase transitions in colloidal systems.     

Preparation, characterization and pharmacokinetics of enrofloxacin-loaded solid lipid nanoparticles: influences of fatty acids

Enrofloxacin-loaded solid lipid nanoparticles (SLN) were prepared using fatty acids (tetradecanoic acid, palmitic acid, stearic acid) as lipid matrix by hot homogenization and ultrasonication method. The effect of fatty acids on the characteristics and pharmacokinetics of the SLN were investigated. The results showed that the encapsulation efficiency and loading capacity of nanoparticles varied with fatty acids in the order of stearic acid>palmitic acid>tetradecanoic acid. Furthermore, stearic acid-SLN had larger particle size, bigger polydispersity index (PDI) and higher zeta potential compared with the other two fatty acid formulated SLN. The SLN showed sustained releases in vitro and the released enrofloxacin had the same antibacterial activity as that of the native enrofloxacin. Although in vitro release exhibited similar patterns, within 24 h the releasing rates of the three formulations were significantly different (tetradecanoic acid-SLN>palmitic acid-SLN>stearic acid-SLN). Pharmacokinetic study after a single dose of intramuscular administration to mice demonstrated that tetradecanoic acid-SLN, palmitic acid-SLN, and stearic acid-SLN increased the bioavailability by 6.79, 3.56 and 2.39 folds, and extended the mean residence time (MRT) of the drug from 10.60 h to 180.36, 46.26 and 19.09 h, respectively. These results suggest that the enrofloxacin-fatty acid SLN are promising formulations for sustained release while fatty acids had significant influences on the characteristics and performances of the SLN.