The production and characteristics of solid lipid nanoparticles (SLNs)

Formulation of curcumin-loaded solid lipid nanoparticles produced by fatty acids coacervation technique

Curcumin (CU) loaded solid lipid nanoparticles (SLNs) of fatty acids (FA) were prepared with a coacervation technique based on FA precipitation from their sodium salt micelles in the presence of polymeric non-ionic surfactants. Myristic, palmitic, stearic, and behenic acids, and different polymers with various molecular weights and hydrolysis grades were employed as lipid matrixes and stabilisers, respectively. Generally, spherical-shaped nanoparticles with mean diameters below 500 nm were obtained, and using only middle-high hydrolysis, grade-polymer SLNs with diameters lower than 300 nm were produced. CU encapsulation efficiency was in the range 28-81% and highly influenced by both FA and polymer type. Chitosan hydrochloride was added to FA SLN formulations to produce bioadhesive, positively charged nanoparticles. A CU-chitosan complex formation could be hypothesised by DSC analysis, UV-vis spectra and chitosan surface tension determination. A preliminary study on HCT-116 colon cancer cells was developed to evaluate the influence of CU-loaded FA SLNs on cell viability.

CLSM as quantitative method to determine the size of drug crystals in a solid dispersion

Purpose

To test whether confocal laser scanning microscopy (CLSM) can be used as an analytical tool to determine the drug crystal size in a powder mixture or a crystalline solid dispersion.

Methods

Crystals of the autofluorescent drug dipyridamole were incorporated in a matrix of crystalline mannitol by physical mixing or freeze-drying. Laser diffraction analysis and dissolution testing were used to validate the particle size that was found by CLSM.

Results

The particle size of the pure drug as determined by laser diffraction and CLSM were similar (D₅₀ of approximately 22 μm). CLSM showed that the dipyridamole crystals in the crystalline dispersion obtained by freeze-drying of less concentrated solutions were of sub-micron size (0.7 μm), whereas the crystals obtained by freeze-drying of more concentrated solutions were larger (1.3 μm). This trend in drug crystal size was in agreement with the dissolution behavior of the tablets prepared from these products.

Conclusion

CLSM is a useful technique to determine the particle size in a powder mixture. Furthermore, CLSM can be used to determine the drug crystal size over a broad size distribution. A limitation of the method is that the drug should be autofluorescent.

Development and evaluation of colloidal modified nanolipid carrier: application to topical delivery of tacrolimus

Low solubility of tacrolimus in carrier matrix and subsequent poor in vivo bioavailability was overcome by constructing modified nanolipid carrier (MNLC) as a novel approach. The aim of this study was to develop MNLC with enhanced drug solubility in carrier lipid matrix using lipophilic solubilizers for topical delivery. Comprehensive characterization of tacrolimus-loaded MNLC (T-MNLC) was carried out for particle size, morphology, and rheology. Lipid modification resulted in the formation of less perfect crystals offering space to accommodate the dissolved drug leading to high entrapment efficiency of 96.66%. Compatibility and mixing behavior of carrier constituents was evaluated using DSC, FT-IR, and (1)H NMR. T-MNLC displayed sufficient stability that could be attributed to possibility to reduce total lipid concentration in carrier. T-MNLC-enriched gels showed significantly higher in vitro drug release, skin permeation, and in vivo bioavailability with dermatopharmacokinetic approach in guinea pigs compared to commercial ointment, Protopic® as reference. Penetration-enhancing effect was confirmed using gamma scintigraphy in vivo in rats. Radioactivity remained localized in skin at the application site avoiding unnecessary biodisposition to other organs with prospective minimization of toxic effects. Skin irritation studies showed T-MNLC to be significantly less irritating than reference. Research work could be concluded as successful development of novel T-MNLC using lipophilic solubilizers to increase the encapsulation efficiency of colloidal lipid carriers with advantage of improved performance in terms of stability and skin localization.

Solid lipid nanoparticles for ocular drug delivery

Ocular drug delivery remains challenging because of the complex nature and structure of the eye. Conventional systems, such as eye drops and ointments, are inefficient, whereas systemic administration requires high doses resulting in significant toxicity. There is a need to develop novel drug delivery carriers capable of increasing ocular bioavailability and decreasing both local and systemic cytotoxicity. Nanotechnology is expected to revolutionize ocular drug delivery. Many nano-structured systems have been employed for ocular drug delivery and yielded some promising results. Solid lipid nanoparticles (SLNs) have been looked at as a potential drug carrier system since the 1990s. SLNs do not show biotoxicity as they are prepared from physiological lipids. SLNs are especially useful in ocular drug delivery as they can enhance the corneal absorption of drugs and improve the ocular bioavailability of both hydrophilic and lipophilic drugs. SLNs have another advantage of allowing autoclave sterilization, a necessary step towards formulation of ocular preparations. This review outlines in detail the various production, characterization, sterilization, and stabilization techniques for SLNs. In-vitro and in-vivo methods to study the drug release profile of SLNs have been explained. Special attention has been given to the nature of lipids and surfactants commonly used for SLN production. A summary of previous studies involving the use of SLNs in ocular drug delivery is provided, along with a critical evaluation of SLNs as a potential ocular delivery system.

Formulation of a novel oxybenzone-loaded nanostructured lipid carriers (NLCs)

The objective of the current study was to formulate oxybenzone into nanostructured lipid carriers (NLCs) to enhance its sunscreening efficacy and safety. NLCs of oxybenzone were prepared by the solvent diffusion method. A complete 2(3) factorial design was used for the evaluation of the prepared oxybenzone NLCs. The study design involves the investigation of the effect of three independent variables namely liquid lipid type (Miglyol 812 and oleic acid), liquid lipid concentration (15% and 30%), and oxybenzone concentration (5% and 10% with respect to total lipids) on the particle size (p.s.) , the entrapment efficiency (EE%) and the in vitro drug release after 8 h. The prepared NLCs were spherical in overall shape and were below 0.8 microm. Miglyol 812 and 30% liquid lipid were found to significantly decrease the p.s. and increase the EE% when compared to oleic acid and 15% liquid lipid. Increasing oxybenzone concentration increased significantly the p.s. but did not affect the EE%. NLCs prepared using Miglyol 812, 15% liquid lipid, and 10% oxybenzone showed slower drug release when compared to those prepared using oleic acid, 30% liquid lipid, and 5% oxybenzone, respectively. The candidate oxybenzone-loaded NLC dispersion was then formulated into gel. The incorporation of oxybenzone into NLCs greatly increased the in vitro sun protection factor and erythemal UVA protection factor of oxybenzone more than six- and eightfold, respectively, while providing the advantage of overcoming side effects of free oxybenzone as evidenced by very low irritation potential.

Characterization and in vivo evaluation of novel lipid-chlorambucil nanospheres prepared using a mixture of emulsifiers for parenteral administration

PURPOSE

The purpose of the study was to develop and evaluate different lipid-based formulations for parenteral administration, as potential novel carrier systems for lipophilic drugs, and to turn an unstable drug such as chlorambucil into a useful one.

METHODS

A two-stage, high-pressure homogenizer was used to yield a very fine monodispersed lipid nanosphere. The strategy of combining egg yolk phospholipid and nonionic emulsifier (Lutrol F 68 and Tween 80) as an emulsifier mixture was adopted to increase safety and tolerance. The final lipid nanospheres, in a lipophilic mixture consisting of three components, monostearin, medium-chain triglycerides and soya oil, were evaluated for physicochemical properties, such as particle size, surface morphology, drug-entrapment efficiency, drug-loading capacity, lyophilization and in vivo drug-release behavior.

RESULTS

A monodispersed lipid nanosphere with a mean particle size ranging from 90 to 150 nm was achieved. The optimized injectable cryoprotectants for lipid nanosphere were sucrose (7.5%) and mannitol (7.5%), which can stabilize the particle size (LD50) at approximately 129 nm after reconstitution. The results show that the formulation can effectively administer anticancer drugs and thus improve patient quality of life.

CONCLUSIONS

The novel lipid nanosphere complex developed is a useful anticancer drug delivery vehicle for parenteral administration. The formulation strategy has the potential for the development of further methods of drug delivery for a wide variety of anticancer drugs.

Solid lipid nanoparticles produced through a coacervation method

Solid lipid nanoparticles (SLN) of fatty acids (FAs) were prepared with a new, solvent-free technique based on FAs precipitation from their sodium salt micelles in the presence of polymeric non-ionic surfactants: this technique was called 'coacervation'. Myristic, palmitic, stearic, arachidic and behenic acid were employed as lipid matrixes. Spherical shaped nanoparticles with mean diameters ranging from 250 to approximately 500 nm were obtained. Different aqueous acidifying solutions were used to precipitate various FAs from their sodium salt micellar solution. Good encapsulation efficiency of Nile Red, a lipophilic model dye, in stearic acid nanoparticles was obtained. The coacervation method seems to be a potentially suitable technique to prepare close to monodisperse nanoparticles for drug delivery purposes.

Controlled crystallization of the lipophilic drug fenofibrate during freeze-drying: elucidation of the mechanism by in-line Raman spectroscopy

We developed a novel process, "controlled crystallization during freeze-drying" to produce drug nanocrystals of poorly water-soluble drugs. This process involves freeze-drying at a relatively high temperature of a drug and a matrix material from a mixture of tertiary butyl alcohol and water, resulting in drug nanocrystals incorporated in a matrix. The aim of this study was to elucidate the mechanisms that determine the size of the drug crystals. Fenofibrate was used as a model lipophilic drug. To monitor the crystallization during freeze-drying, a Raman probe was placed just above the sample in the freeze-dryer. These in-line Raman spectroscopy measurements clearly revealed when the different components crystallized during freeze-drying. The solvents crystallized only during the freezing step, while the solutes only crystallized after the temperature was increased, but before drying started. Although the solutes crystallized only after the freezing step, both the freezing rate and the shelf temperature were critical parameters that determined the final crystal size. At a higher freezing rate, smaller interstitial spaces containing the freeze-concentrated fraction were formed, resulting in smaller drug crystals (based on dissolution data). On the other hand, when the solutes crystallized at a lower shelf temperature, the degree of supersaturation is higher, resulting in a higher nucleation rate and consequently more and therefore smaller crystals. In conclusion, for the model drug fenofibrate, a high freezing rate and a relatively low crystallization temperature resulted in the smallest crystals and therefore the highest dissolution rate.

Nanostructured lipid carriers for parenteral delivery of silybin: Biodistribution and pharmacokinetic studies

The objective of the present study was to explore the potential of nanostructured lipid carriers (NLCs) for the intravenous delivery of silybin, a poorly water-soluble antihepatopathy agent. Silybin-NLC was prepared by the method of emulsion evaporation at a high temperature and solidification at a low temperature. The resultant NLC had a mean size 232.1 nm and a zeta potential of -20.7 mV. The differential scanning calorimetry (DSC) analysis indicated that silybin was not in crystalline state in the NLC. In vitro data for release of the drug from silybin-NLC was fitted to a two-stage exponential kinetic model. The pharmacokinetics and tissue distribution of silybin-NLC were studied after intravenous administration using New Zealand rabbits and Kunming mice as experimental animals. A silybin control solution was studied parallelly. Silybin-NLC showed higher AUC (area under tissue concentration-time curve) values and circulated in the blood stream for a longer time compared with silybin solution. The tissue distribution demonstrated a high uptake of silybin-NLC in RES organs particularly in liver. These results indicate that NLC is a potential sustained release and targeting system for silybin.

Translocation of cell penetrating peptide engrafted nanoparticles across skin layers

The objective of the current study was to evaluate the ability of cell penetrating peptides (CPP) to translocate the lipid payload into the skin layers. Fluorescent dye (DID-oil) encapsulated nano lipid crystal nanoparticles (FNLCN) were prepared using Compritol, Miglyol and DOGS-NTA-Ni lipids by hot melt homogenization technique. The FNLCN surface was coated with TAT peptide (FNLCNT) or control YKA peptide (FNLCNY) and in vitro rat skin permeation studies were performed using Franz diffusion cells. Observation of lateral skin sections obtained using cryotome with a confocal microscope demonstrated that skin permeation of FNLCNT was time dependent and after 24h, fluorescence was observed upto a depth of 120 microm which was localized in the hair follicles and epidermis. In case of FNLCN and FNLCNY formulations fluorescence was mainly observed in the hair follicles. This observation was further supported by confocal Raman spectroscopy where higher fluorescence signal intensity was observed at 80 and 120 microm depth with FNLCNT treated skin and intensity of fluorescence peaks was in the ratio of 2:1:1 and 5:3:1 for FNLCNT, FNLCN, and FNLCNY treated skin sections, respectively. Furthermore, replacement of DID-oil with celecoxib (Cxb), a model lipophilic drug showed similar results and after 24h, the CXBNT formulation increased the Cxb concentration in SC by 3 and 6 fold and in epidermis by 2 and 3 fold as compared to CXBN and CXBNY formulations respectively. Our results strongly suggest that CPP can translocate nanoparticles with their payloads into deeper skin layers.

Chemical and structural investigation of lipid nanoparticles: drug-lipid interaction and molecular distribution

Lipid nanoparticles are a promising alternative to existing carriers in chemical or drug delivery systems. A key challenge is to determine how chemicals are incorporated and distributed inside nanoparticles, which assists in controlling chemical retention and release characteristics. This study reports the chemical and structural investigation of gamma-oryzanol loading inside a model lipid nanoparticle drug delivery system composed of cetyl palmitate as solid lipid and Miglyol 812 as liquid lipid. The lipid nanoparticles were prepared by high pressure homogenization at varying liquid lipid content, in comparison with the gamma-oryzanol free systems. The size of the lipid nanoparticles, as measured by the photon correlation spectroscopy, was found to decrease with increased liquid lipid content from 200 to 160 nm. High-resolution proton nuclear magnetic resonance ((1)H-NMR) measurements of the medium chain triglyceride of the liquid lipid has confirmed successful incorporation of the liquid lipid in the lipid nanoparticles. Differential scanning calorimetric and powder x-ray diffraction measurements provide complementary results to the (1)H-NMR, whereby the crystallinity of the lipid nanoparticles diminishes with an increase in the liquid lipid content. For the distribution of gamma-oryzanol inside the lipid nanoparticles, the (1)H-NMR revealed that the chemical shifts of the liquid lipid in gamma-oryzanol loaded systems were found at rather higher field than those in gamma-oryzanol free systems, suggesting incorporation of gamma-oryzanol in the liquid lipid. In addition, the phase-separated structure was observed by atomic force microscopy for lipid nanoparticles with 0% liquid lipid, but not for lipid nanoparticles with 5 and 10% liquid lipid. Raman spectroscopic and mapping measurements further revealed preferential incorporation of gamma-oryzanol in the liquid part rather than the solid part of in the lipid nanoparticles. Simple models representing the distribution of gamma-oryzanol and lipids (solid and liquid) inside the lipid nanoparticle systems are proposed.

Delivery of daunorubicin to cancer cells with decreased toxicity by association with a lipidic nanoemulsion that binds to LDL receptors

A lipidic nanoemulsion termed LDE concentrates in neoplastic cells after injection into the bloodstream and thus can be used as a drug carrier to tumour sites. The chemotherapeutic agent daunorubicin associates poorly with LDE; the aim of this study was to clarify whether the derivatization of daunorubicin by the attachment of an oleyl group increases the association with LDE, and to test the cytotoxicity and animal toxicity of the new preparation. The association of oleyldaunorubicin (oDNR) to LDE showed high yield (93 ± 2% and 84 ± 4% at 1:10 and 1:5 drug:lipid mass, respectively) and was stable for at least 20 days. Association with oDNR increased the LDE particle diameter from 42 ± 4 nm to 75 ± 6 nm. Cytotoxicity of LDE-oDNR was reduced two-fold in HL-60 and K-562 cell lines, fourteen-fold in B16 cells and nine-fold in L1210 cells when compared with commercial daunorubicin. When tested in mice, LDE-oDNR showed remarkable reduced toxicity (maximum tolerated dose > 253 μmol kg−1, compared with <3 μmol kg−1 for commercial daunorubicin). At high doses, the cardiac tissue of LDE-oDNR-treated animals had much smaller structural lesions than with commercial daunorubicin. LDE-oDNR is therefore a promising new preparation that may offer superior tolerability compared with commercial daunorubicin.

Evaluation of solid lipid microparticles produced by spray congealing for topical application of econazole nitrate

Objectives

The aims of this study were to evaluate the suitability of the spray congealing technique to produce solid lipid microparticles (SLMs) for topical administration and to study the skin permeation of a drug from SLMs compared with solid lipid nanoparticles (SLNs).

Methods

Econazole nitrate was used as model drug and Precirol ATO 5 as the lipidic carrier. SLMs and SLNs were both prepared at 5: 1, 10: 1 and 12.5: 1 lipid: drug weight ratios and characterised in terms of particle size, morphology, encapsulation efficiency and chemical analysis of the particle surface. SLMs and SLNs were also incorporated into HPMC K 100M hydrogels for ex-vivo drug permeation tests using porcine epidermis.

Key findings

SLMs had particle sizes of 18–45 μm, while SLNs showed a mean diameter of 130–270 nm. The encapsulation efficiency was 80–100%. Permeation profiles of econazole nitrate were influenced by both particle size (significant difference until 9 h) and the amount of lipid.

Conclusions

The results confirm the usefulness of SLNs as carriers for topical administration and suggest the potential of SLMs for the delivery of drugs to the skin.

Lipid nanoparticles: effect on bioavailability and pharmacokinetic changes

The main aim of pharmaceutical technology research is the design of successful formulations for effective therapy, taking into account several issues including therapeutic requirements and patient compliance. In this regard, several achievements have been reported with colloidal carriers, in particular with lipid nanoparticles, due to their unique physicochemical properties. For several years these carriers have been showing potential success for several administration routes, namely oral, dermal, parenteral, and, more recently, for pulmonary and brain targeting. The present chapter provides a review of the use of solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC) to modify the release profile and the pharmacokinetic parameters of active pharmaceutical ingredients (APIs) incorporated in these lipid matrices, aiming to modify the API bioavailability, either upwards or downwards depending on the therapeutic requirement. Definitions of the morphological characteristics, surface properties, and polymorphic structures will also be given, emphasizing their influence on the incorporation parameters of the API, such as yield of production, loading capacity, and encapsulation efficiency.

Preparation and characterization of silybin-loaded nanostructured lipid carriers

Nanostructured lipid carriers (NLC) are a new generation of lipid nanoparticles, which are produced by controlled mixing of solid lipids with spatially incompatible liquid lipids leading to special nanostructures with improved drug incorporation and release properties. In this study, silybin-loaded nanostructured lipid carriers with various liquid lipid content were successfully prepared by the method of emulsion evaporation at a high temperature and solidification at a low temperature. The size and morphology of nanoparticles were significantly influenced by the liquid lipid content. As the liquid lipid content increased to 20 wt%, the obtained particles showed distinguished smaller size. Compared with solid lipid nanoparticles (SLN), NLC presented improved drug loading capacity which increased with increasing the liquid lipid content. The differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analysis indicated that the incorporation of liquid lipids could interfere with the crystallization of solid lipids. The drug in vitro release behavior from NLC displayed a biphasic drug release pattern with burst release at the initial stage and prolonged release afterwards, and the successful controlled release rate can be achieved by controlling the liquid lipid content.

Preparation of drug nanocrystals by controlled crystallization: application of a 3-way nozzle to prevent premature crystallization for large scale production

In a previous study we have developed a novel process to produce drug nanocrystals. This process, "controlled crystallization during freeze-drying" has shown to be a successful method to increase the dissolution rate of poorly water-soluble drugs [de Waard, H., Hinrichs, W.L.J., Frijlink, H.W., 2008. A novel bottom-up process to produce drug nanocrystals: controlled crystallization during freeze drying. J. Control. Release 128, 179-183]. This process consisted of two steps: a solution of a matrix material (mannitol) in water was mixed with a solution of a drug (fenofibrate) in tertiary butyl alcohol (TBA). This mixture was frozen and subsequently freeze-dried at relatively high temperature (-25 degrees C). Since the solution of matrix and drug in the water-TBA mixture is thermodynamically unstable, it had to be frozen immediately and fast after preparation to prevent premature crystallization of the drug resulting in the formation too large drug crystals. Therefore, small quantities were manually mixed in a vial and this vial was immersed in liquid nitrogen. To make this process ready for large scale production, the modification of this batch process to a semi-continuous process by the application of a 3-way nozzle was studied. With this nozzle, the aqueous and TBA-solutions were pumped into the nozzle via two separate channels and mixed just at the moment they left the nozzle. Thorough mixing was facilitated by the atomizing air, supplied via the third channel. Since the mixture was sprayed immediately into liquid nitrogen, premature crystallization was prevented. A further advantage was that the atomizing air generated small droplets which were directly immersed into liquid nitrogen. Consequently, the mixture was frozen even faster than in the batch process. This resulted in a reduced size of the drug crystals and hence a higher dissolution rate. Therefore, using the semi-continuous process does not only result in successfully making this process suitable for large scale production of the controlled crystallized dispersions, but it also results in a better product.

Diazepam-loaded solid lipid nanoparticles: design and characterization

The aim of the present study was to investigate the feasibility of the inclusion of a water-insoluble drug (diazepam, DZ) into solid lipid nanoparticles (SLNs), which offer combined advantages of rapid onset and prolonged release of the drug. This work also describes a new approach to prepare suppositories containing DZ-loaded SLN dispersions, as potential drug carrier for the rectal route. Modified high-shear homogenization and ultrasound techniques were employed to prepare SLNs. The effect of incorporation of different concentrations of Compritol ATO 888 or Imwitor 900K and Poloxamer 188 or Tween 80 was investigated. Results showed that varying the type or concentration of lipid matrix or surfactant had a noticeable influence on the entrapment efficiencies, particle size, and release profiles of prepared SLNs. Differential scanning calorimetry and X-ray diffraction measurements showed that the majority of SLNs possessed less ordered arrangements of crystals than the corresponding bulk lipids, which was favorable for increasing the drug loading capacity. Transmission electron microscopy and laser diffractometry studies revealed that the prepared nanoparticles were round and homogeneous and 60% of the formulations were less than 500 nm. Additionally, SLN formulations showed significant (P < 0.05) prolonged release than DZ solution. The subsequent step encompassed the preparation and evaluation of SLN-based suppositories utilizing SLN formulations that illustrated optimal release profiles. The in vitro release of DZ from the suppositories prepared using DZ-loaded SLN dispersions (equivalent to 2 mg DZ) was significantly (P < 0.05) extended compared to suppositories containing 2 mg DZ free drug.

Testosterone solid lipid microparticles for transdermal drug delivery. Formulation and physicochemical characterization

PURPOSE

The main objective of the study was to formulate and characterize testosterone (TS) solid lipid microparticles (SLM) to be applied as a transdermal delivery system.

METHODS

Testosterone SLMs were formulated using an emulsion melt homogenization method. Various types and concentrations of fatty materials, namely glyceryl monostearate (GM), glyceryl distearate (GD), stearic acid (SA) and glyceryl behanate (GB) were used. The formulations contained 2.5 or 5 mg TS g(-1). Morphology, particle size, entrapment efficiency (EE), rheological properties and thermal behaviour of the prepared SLM were examined. In vitro release characteristics of TS from various prepared SLM were also evaluated over 24 h using a vertical Franz diffusion cell. In addition, the effect of storage and freeze-drying on particle size and release pattern of TS from the selected formulation was evaluated.

RESULTS

The results indicated that the type of lipid affected the morphology and particle size of SLM. A relatively high drug percentage entrapment efficiency ranging from 80.7-95.7% was obtained. Rheological studies showed plastic flow characteristics of the prepared formulations. DSC examination revealed that TS existed in amorphous form in the prepared SLM. Release studies revealed the following rank order of TS permeation through cellophane membrane after application of various formulations: 5% GM < 5% GD < 5% SA < 5% GB < 2.5% GM < 2.5% SA < 10% GD < 10% GB. The drug permeation through excised abdomen rat skin after application of 10% GB-2.5 mg TS g(-1) SLM was lower than that permeated through cellophane membrane. Moreover, SLM containing 10% GB-2.5 mg TS g(-1) stored at 5 degrees C showed good stability as indicated by the release study and particle size analysis. Trehalose showed high potential as a cryoprotectant during freeze drying of the selected SLM formulation.

CONCLUSIONS

The developed TS SLM delivery system seemed to be promising as a TS transdermal delivery system.

Development and evaluation of lipid nanoparticles for camptothecin delivery: a comparison of solid lipid nanoparticles, nanostructured lipid carriers, and lipid emulsion

AIM

Camptothecin is an anticancer drug that acts against a broad spectrum of tumors. The clinical application of camptothecin is limited by its insolubility, instability, and toxicity problems. The aim of this study was to develop and characterize lipid nanoparticles with different lipid cores which can circumvent these problems.

METHODS

Lipid nanoparticles made of Precirol (solid lipid nanoparticles; SLN-P), Compritol (SLN-C), Precirol+squalene (nanostructured lipid carriers; NLC), and squalene (a lipid emulsion; LE) as the lipid core material were prepared. These systems were assessed and compared by evaluating the mean diameter, surface charge, molecular environment, camptothecin release, and cell viability against a melanoma. The safety and storage stability of these systems were also preliminarily examined.

RESULTS

The particle size ranged from 190 to 310 nm, with the NLC and LE showing the smallest and largest sizes, respectively. The in vitro drug release occurred in a sustained manner in decreasing order as follows: LE> NLC> SLN-P> SLN-C. It was found that varying the type of inner phase had profound effects on cell viability. The SLN-P generally showed higher cytotoxicity than the free control. The treatment of melanomas with the camptothecin-loaded SLN-C and NLC yielded cytotoxicity comparable to that of the free form. The percentage of erythrocyte hemolysis by all nanoparticles was < or =5%, suggesting a good tolerance to lipid nanoparticles.

CONCLUSION

The results collectively suggest that the SLN-P may have the potential to serve as a delivery system for parenteral camptothecin administration because of the sustained drug release, strong cytotoxicity, limited hemolysis, and good storage stability.

The effect of cetyl palmitate crystallinity on physical properties of gamma-oryzanol encapsulated in solid lipid nanoparticles

This present study was aimed at investigating the effect of the crystallinity of cetyl palmitate based solid lipid nanoparticles (SLNs) on the physical properties of γ-oryzanol-loaded SLNs. SLNs consisting of varying ratios of cetyl palmitate and γ-oryzanol were prepared. Their hydrodynamic diameters were in the range 210-280 nm and the zeta potentials were in the range -27 to -35 mV. The size of SLNs increased as the amount of cetyl palmitate decreased whereas no significant change of zeta potentials was found. Atomic force microscopy pictures indicated the presence of disc-like particles. The crystallinity of SLNs, determined by differential scanning calorimetry and powder x-ray diffraction, was directly dependent on the ratio of cetyl palmitate to γ-oryzanol and decreased with decreasing cetyl palmitate content in the lipid matrix. Varying this ratio in the lipid mix resulted in a shift in the melting temperature and enthalpy, although the SLN structure remained unchanged as an orthorhombic lamellar lattice. This has been attributed to a potential inhibition by γ-oryzanol during lipid crystal growth as well as a less ordered structure of the SLNs. The results revealed that the crystallinity of the SLNs was mainly dependent on the solid lipid, and that the crystallinity has an important impact on the physical characteristics of active-loaded SLNs.

Lipid nanoparticles for alkyl lysophospholipid edelfosine encapsulation: Development and in vitro characterization

The ether lipid 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine, edelfosine (ET-18-OCH(3)) is the prototype molecule of a promising class of antitumor drugs named alkyl-lysophospholipid analogues (ALPs) or antitumor ether lipids. This drug presents a very important drawback as can be the dose dependent haemolysis when administered intravenously. Lipid nanoparticles have been lately proposed for different drug encapsulation as an alternative to other controlled release delivery systems, such as liposomes or polymeric nanoparticles. The aim of this study was to develop a lipid nanoparticulate system that would decrease systemic toxicity as well as improve the therapeutic potential of the drug. Lipids employed were Compritol 888 ATO and stearic acid. The nanoparticles were characterized by photon correlation spectroscopy for size and size distribution, and atomic force microscopy (AFM) was used for the determination of morphological properties. By both differential scanning calorimetry (DSC) and X-ray diffractometry, crystalline behaviour of lipids and drug was assessed. The drug encapsulation efficiency and the drug release kinetics under in vitro conditions were measured by HPLC-MS. It was concluded that Compritol presents advantages as a matrix material for the manufacture of the nanoparticles and for the controlled release of edelfosine.

Lipospheres as carriers for topical delivery of aceclofenac: preparation, characterization and in vivo evaluation

The purpose of this study was to prepare lipospheres containing aceclofenac intended for topical skin delivery with the aim of exploiting the favorable properties of this carrier system and developing a sustained release formula to overcome the side effects resulting from aceclofenac oral administration. Lipospheres were prepared using different lipid cores and phospholipid coats adopting melt and solvent techniques. Characterization was carried out through photomicroscopy, scanning electron microscopy, particle size analysis, DSC, In vitro drug release and storage study. The anti-inflammatory effect of liposphere systems was assessed by the rat paw edema technique and compared to the marketed product. Results revealed that liposphere systems were able to entrap aceclofenac at very high levels (93.1%). The particle size of liposphere systems was well suited for topical drug delivery. DSC revealed the molecular dispersion of aceclofenac when incorporated in lipospheres. Both entrapment efficiency and release were affected by the technique of preparation, core and coat types, core to coat ratio and drug loading. Lipospheres were very stable after 3 months storage at 2-8 degrees C manifested by low leakage rate (less than 7%) and no major changes in particle size. Finally, liposphere systems were found to possess superior anti-inflammatory activity compared to the marketed product in both lotion and paste consistencies. Liposphere systems proved to be a promising topical system for the delivery of aceclofenac as they possessed the ability to entrap the drug at very high levels and high stability, and to sustain the anti-inflammatory effect of the drug.

The effects of cryoprotectants on the freeze-drying of ibuprofen-loaded solid lipid microparticles (SLM)

The effects of cryoprotectants on the diameter and the entrapment efficiency of ibuprofen-loaded solid lipid microparticles (SLM) during the freeze-drying process were investigated extensively. The SLM were prepared by the emulsion-congealing technique in which a glycerol behenate was used as the lipid matrix for the SLM and a soybean lecithin/bile salt used as the stabilizer. Also, trehalose, glucose, mannitol, and sucrose were chosen as the cryoprotectants. Trehalose and glucose proved to be the most effective in preventing particles aggregation and in inhibiting leakage from drug-loaded particles during the SLM freeze-drying process. The most suitable concentrations were proved to be 15% and 5% (wt), respectively.

Development and evaluation of topical formulation containing solid lipid nanoparticles of vitamin A

The purpose of this research was to investigate novel particulate carrier system such as solid lipid nanoparticles (SLN) for topical application of vitamin A palmitate and to study its beneficial effects on skin. Topical gels enriched with SLN of vitamin A were prepared. The solid lipid nanoparticulate dispersion was prepared using high-pressure homogenization technique and was incorporated into polymeric gels of Carbopol, Pemulen, Lutrol, and Xanthan gum for convenient application. The nanoparticulate dispersion and its gels were evaluated for various parameters such as particle size, in vitro drug release, in vitro penetration, in vivo skin hydration, and skin irritation. The solid lipid nanoparticulate dispersion showed mean particle size of 350 nm. Differential scanning calorimetry studies revealed no drug-excipient incompatibility. In vitro release profile of vitamin A palmitate from nanoparticulate dispersion and its gel showed prolonged drug release up to 24 hours, which could be owing to embedment of drug in the solid lipid core. In vitro penetration studies showed almost 2 times higher drug concentration in the skin with lipid nanoparticle-enriched gel as compared with conventional gel, thus indicating better localization of the drug in the skin. In vivo skin hydration studies in albino rats revealed increase in the thickness of the stratum corneum with improved skin hydration. The developed formulation was nonirritant to the skin with no erythema or edema and had primary irritation index of 0.00. Thus it can be concluded that SLN represents a promising particulate carrier having controlled drug release, improved skin hydration, and potential to localize the drug in the skin with no skin irritation.

Paclitaxel-loaded lipid nanoparticles prepared by solvent injection or ultrasound emulsification

Lipid nanoparticles were fabricated as an injectable carrier system for paclitaxel. The components for the lipid matrix were based on phospholipids, and sucrose fatty acid ester was used as an emulsifier. Formulation prepared with solvent injection has a slightly larger particle size (187.6 nm) than the formulation (147.7 nm) prepared with ultrasound emulsification. Differential scanning calorimetry results indicated that paclitaxel entrapped in the lipid nanoparticles existed in an amorphous state in the lipid matrix. In vitro drug release was rather slow; only 12.5-16.5% of the drug released from the formulations within 14 days. Lipid nanoparticles demonstrated their potential as a promising pharmaceutical formulation of paclitaxel.

Inorganic nanoparticles for transfection of mammalian cells and removal of viruses from aqueous solutions

Owing to their small size, synthetic nanoparticles show unprecedented biophysical and biochemical properties which may foster novel advances in life-science research. Using flame-spray synthesis technology we have produced non-coated aluminum-, calcium-, cerium-, and zirconium-derived inorganic metal oxide nanoparticles which not only exhibit high affinity for nucleic acids, but can sequester such compounds from aqueous solution. This non-covalent DNA-binding capacity was successfully used to transiently transfect a variety of mammalian cells including human, reaching transfection efficiencies which compared favorably with classic calcium phosphate precipitation (CaP) procedures and lipofection. In this straightforward protocol, transfection was enabled by simply mixing nanoparticles with DNA in solution prior to addition to the target cell population. Transiently transfected cells showed higher production levels of the human secreted glycoprotein SEAP compared to isogenic populations transfected with established technologies. Inorganic metal oxide nanoparticles also showed a high binding capacity to human-pathogenic viruses including adenovirus, adeno-associated virus and human immunodeficiency virus type 1 and were able to clear these pathogens from aqueous solutions. The DNA transfection and viral clearance capacities of inorganic metal oxide nanoparticles may provide cost-effective biopharmaceutical manufacturing and water treatment in developing countries.

A critical study of novel physically structured lipid matrices composed of a homolipid from Capra hircus and theobroma oil

There is increasing interest in drug formulation using lipids. In this study, some physically structured lipid matrices were formulated and characterized for drug delivery applications. Lipid matrices containing a novel homolipid from Capra hircus (goat fat) and theobroma oil, at 25, 50 and 75% (w/w) concentration of the homolipid were formulated by fusion. The lipid matrices were subjected to some characterization procedures such as differential scanning calorimetry (DSC) to ascertain their supramolecular properties, small angle X-ray diffraction (SAXD), wide angle X-ray diffraction (WAXD), polarized light microscopy (PLM) and isothermal heat conduction microcalorimetry (IMC). The internal structures of some selected lipid matrices were also studied by freeze-fracture transmission electron microscopy (FFTEM). DSC results obtained indicated that goat fat has a pre-transition at 15.9 +/- 0.2 degrees C (after 1 week) and melts completely with two detectable melting peaks at 33.0 +/- 0.2 and 49.9 +/- 0.1 degrees C, and total enthalpy of 99.9 +/- 2.5 mJ/mg determined after 6 weeks of preparation. The melting enthalpy of goat fat changed after 3 weeks but remained constant after 6 weeks while the melting enthalpy of the lipid matrix containing 50% (w/w) goat fat changed after 3 and 6 weeks. An increase in lower melting peak was observed in the lipid matrix containing 25% (w/w) goat fat after 6 weeks. WAXD and SAXD of the physically structured lipid matrices showed reflections of the different pure lipids but new interferences were detected in WAXD mostly between 2theta=17.5 degrees and 2theta=27.5 degrees . PLM observation revealed the presence of Maltese crosses for the homolipid at 37 degrees C, which disappeared upon heating at 51.0 degrees C. PLM of the structured lipid matrix containing 25% (w/w) goat fat showed distinct crystal growth after 4 weeks among the admixtures. However, IMC studies did not reveal any change in recrystallization behaviour in this lipid matrix within 24 h. Analysis of the crystallization exotherms indicated that the lipid matrix containing 50% (w/w) goat fat showed unique crystallization kinetics and possessed the lowest Avrami exponent, while goat fat alone showed slight change within the first 45 min of isothermal crystallization. Physically structured lipid matrix containing 75% (w/w) goat fat possessed the lowest growth rate constant.

A new polymer-lipid hybrid nanoparticle system increases cytotoxicity of doxorubicin against multidrug-resistant human breast cancer cells

PURPOSE

This work is intended to develop and evaluate a new polymer-lipid hybrid nanoparticle system that can efficiently load and release water-soluble anticancer drug doxorubicin hydrochloride (Dox) and enhance Dox toxicity against multidrug-resistant (MDR) cancer cells.

METHODS

Cationic Dox was complexed with a new soybean-oil-based anionic polymer and dispersed together with a lipid in water to form Dox-loaded solid lipid nanoparticles (Dox-SLNs). Drug loading and release properties were measured spectrophotometrically. The in vitro cytotoxicity of Dox-SLN and the excipients in an MDR human breast cancer cell line (MDA435/LCC6/MDR1) and its wild-type line were evaluated by trypan blue exclusion and clonogenic assays. Cellular uptake and retention of Dox were determined with a microplate fluorometer.

RESULTS

Dox-SLNs were prepared with a drug encapsulation efficiency of 60-80% and a particle size range of 80-350 nm. About 50% of the loaded drug was released in the first few hours and an additional 10-20% in 2 weeks. Treatment of the MDR cells with Dox-SLN resulted in over 8-fold increase in cell kill when compared to Dox solution treatment at equivalent doses. The blank SLN and the excipients exhibited little cytotoxicity. The biological activity of the released Dox remained unchanged from fresh, free Dox. Cellular Dox uptake and retention by the MDR cells were both significantly enhanced (p < 0.05) when Dox was delivered in Dox-SLN form.

CONCLUSIONS

The new polymer-lipid hybrid nanoparticle system is effective for delivery of Dox and enhances its efficacy against MDR breast cancer cells.