Drug Release from Differently Structured Monoolein/Poloxamer Nanodispersions Studied with Differential Pulse Polarography and Ultrafiltration at Low Pressure

Comparative study on the performance of monoolein cubic nanoparticles and trimyristin solid lipid nanoparticles as carriers for docetaxel

Nowadays the application of lipid nanoparticles as carriers for the delivery of anticancer drugs gained great attention in cancer therapy. Solid lipid nanoparticles (SLN_s) and cubic nanoparticles (cubosomes) are considered as promising carriers in cancer therapy. The comparison of these two lipid nanoparticles as efficient carriers for the anticancer drug docetaxel was our main goal in this study. Both nanoparticles were prepared by the hot melt homogenization technique followed by measurement of particle size, zeta potential, entrapment efficiency and in vitro release of docetaxel. An advanced technique has been applied to measure the release of docetaxel from these nanoparticles using small unilamellar vesicles (SUV_s) as acceptor particles which resemble many compartments in our body. All prepared nanoparticles revealed a neutral zeta potential with particle sizes of about 200 nm. While SUV_s showed a negative surface charge with a zeta potential of -55 mV, cubosomes showed higher entrapment efficiency and a slower docetaxel release compared to SLN_s. Additionally, cubosomes improved in vitro cytotoxicity as well as the in vivo antitumor inhibition of docetaxel compared to SLN_s and docetaxel solution. Overall, our results showed that incorporation of docetaxel into cubosomes could enhance its in vitro and in vivo performance compared to docetaxel incorporated into SLN_s.

Reliable release testing for nanoparticles with the NanoDis System, an innovative sample and separate technique

One of the critical quality attributes of nanoparticle formulations is drug release. Their release properties should therefore be well characterized with predictive and discriminative methods. However, there is presently still no standard method for the release testing of extended release nanoformulations. Dialysis techniques are widely used in the literature but suffer from severe drawbacks. Burst release of formulations can be masked by slow permeation kinetics of the free drug through the dialysis membrane, saturation in the membrane, and absence of agitation in the membrane. In this study, the release profile of poly(lactic co-glycolic) (PLGA) nanocapsules loaded with all-trans retinoic acid was characterized using an innovative sample and separate set-up, the NanoDis System, and compared to the release profile measured with a dialysis technique. The NanoDis System showed clear superiority over the dialysis method and was able to accurately characterize the burst release from the capsules and furthermore discriminate between different all-trans retinoic acid nanoparticle formulations.

Bioavailability and Antidiabetic Activity of Gliclazide-Loaded Cubosomal Nanoparticles

In this study, gliclazide-loaded cubosomal particles were prepared for improving the oral bioavailability and antidiabetic activity of gliclazide. Four formulations of gliclazide-loaded cubosomal nanoparticles dispersions were prepared by the emulsification method using four different concentrations of glyceryl monooleate (GMO) and poloxamer 407 (P407) as the stabilizer. The prepared formulations were in vitro and in vivo evaluated. In vitro, the prepared gliclazide-loaded cubosomal dispersions exhibited disaggregated regular poly-angular particles with a nanometer-sized particle range from 220.60 ± 1.39 to 234.00 ± 2.90 nm and entrapped 73.84 ± 3.03 to 88.81 ± 0.94 of gliclazide. In vitro gliclazide release from cubosomal nanoparticles revealed an initially higher drug release during the first 2 h in acidic pH medium; subsequently, a comparatively higher drug release in alkaline medium relative to gliclazide suspension was observed. An in vivo absorption study in rats revealed a two-fold increase in the bioavailability of gliclazide cubosomal formulation relative to plain gliclazide suspension. Moreover, the study of in vivo hypoglycemic activity indicated that a higher percentage reduction in glucose level was observed after the administration of gliclazide cubosomal nanoparticles to rats. In conclusion, gliclazide-loaded cubosomal nanoparticles could be a promising delivery system for improving the oral absorption and antidiabetic activity of gliclazide.

Transfer of Lipophilic Drugs from Nanoemulsions into Lipid-Containing Alginate Microspheres

Knowledge about the release behavior and drug retention properties of colloidal carriers is of essential importance for quality control as well as to predict in vivo performance. When conducting release studies from such systems, the release media should preferentially contain lipophilic acceptor components in order to mimic physiological conditions. In this study, transfer from a trimyristin nanoemulsion into lipid-containing hydrogel beads was investigated for fenofibrate, cannabidiol, retinyl acetate, orlistat, and lumefantrine. To generate the acceptor system, a trimyristin nanoemulsion was incorporated into Ca-alginate microspheres (mean diameter ~40 µm) with a spraying method. Using this approach, the advantages of small lipophilic acceptor particles with a large interfacial area were combined with a single separation process from the donor via a filtration step. The method was applicable to distinguish between fast (fenofibrate) and slow drug transfer (lumefantrine) with good time resolution. Lipophilicity, estimated according to the calculated logP value of the respective drug, was a major factor influencing the transfer performance: the higher the logP value, the slower the transfer. This experimental setup is a promising technique to investigate the release of poorly water-soluble drugs from various types of nanocarriers under closer to physiological conditions than with many other methods currently applied.

In Vitro Drug Dissolution/Permeation Testing of Nanocarriers for Skin Application: a Comprehensive Review

This review highlights in vitro drug dissolution/permeation methods available for topical and transdermal nanocarriers that have been designed to modulate the propensity of drug release, drug penetration into skin, and permeation into systemic circulation. Presently, a few of USFDA-approved in vitro dissolution/permeation methods are available for skin product testing with no specific application to nanocarriers. Researchers are largely utilizing the in-house dissolution/permeation testing methods of nanocarriers. These drug release and permeation methods are pending to be standardized. Their biorelevance with reference to in vivo plasma concentration-time profiles requires further exploration to enable translation of in vitro data for in vivo or clinical performance prediction.

Indomethacin functionalised poly(glycerol adipate) nanospheres as promising candidates for modified drug release

The linear polyester poly(glycerol adipate) (PGA) with its free pendant hydroxyl groups was covalently grafted with indomethacin which yields polymeric prodrugs. It was possible to produce nanospheres with narrow particle size distribution of these polymer-drug conjugates with an optimized interfacial deposition method. Nanospheres were characterized by zeta potential measurements, dynamic light scattering, electron microscopy and nanoparticle tracking analysis. Moreover, cell viability studies and cytotoxicity tests in three different cell lines were carried out showing low toxicity for three different degrees of grafting. In addition, the nanospheres had (in contrast to the free drug) low hemolytic activity in vitro. Release studies of nanodispersions are challenging. The use of a specially developed setup with highly porous aluminum oxide membranes enabled us to overcome problems associated with other setups (e.g. dialysis membranes). A slow and controlled release profile without any burst was observed over 15 days. The results indicate that indomethacin-PGA conjugates can be formulated successfully as nanospheres with the desired characteristics of small size with narrow distribution, controlled drug release and low toxicity. The newly developed particles have the potential to improve the therapy of inflammation and associated diseases.

Improved delivery of poorly soluble compounds using nanoparticle technology: a review

Although a large number of new drug molecules with varied therapeutic potentials have been discovered in the recent decade, yet most of them are still in developmental process. This can be attributed to the limited aqueous solubility which governs the bioavailability of such drug molecules. Hence, there is a requisite for a technology-based product (formulation) in order to overcome such issues without compromising on the therapeutic response. The purpose of this review is to provide an insight to the formulation of drug nanoparticles for enhancing solubility and dissolution velocity with concomitant enhancement in bioavailability. In the recent decade, nanonization has evolved from a concept to reality owing to its versatile applications, especially in the development of drugs having poor solubility. In this review, a relatively simple and scalable approach for the manufacture of drug nanoparticles and latest characterization techniques utilized to evaluate the drug nanoparticles are discussed. The drug nanoparticulate approach described herein provides a general applicability of the platform technology in designing a formulation for drugs associated with poor aqueous solubility.

Building the design, translation and development principles of polymeric nanomedicines using the case of clinically advanced poly(lactide(glycolide))-poly(ethylene glycol) nanotechnology as a model: An industrial viewpoint

The design of the first polymeric nanoparticles could be traced back to the 1970s, and has thereafter received considerable attention, as evidenced by the significant increase of the number of articles and patents in this area. This review article is an attempt to take advantage of the existing literature on the clinically tested and commercialized biodegradable PLA(G)A-PEG nanotechnology as a model to propose quality building and outline translation and development principles for polymeric nano-medicines. We built such an approach from various building blocks including material design, nano-assembly - i.e. physicochemistry of drug/nano-object association in the pharmaceutical process, and release in relevant biological environment - characterization and identification of the quality attributes related to the biopharmaceutical properties. More specifically, as envisaged in a translational approach, the reported data on PLA(G)A-PEG nanotechnology have been structured into packages to evidence the links between the structure, physicochemical properties, and the in vitro and in vivo performances of the nanoparticles. The integration of these bodies of knowledge to build the CMC (Chemistry Manufacturing and Controls) quality management strategy and finally support the translation to proof of concept in human, and anticipation of the industrialization takes into account the specific requirements and biopharmaceutical features attached to the administration route. From this approach, some gaps are identified for the industrial development of such nanotechnology-based products, and the expected improvements are discussed. The viewpoint provided in this article is expected to shed light on design, translation and pharmaceutical development to realize their full potential for future clinical applications.

Comparison of different in vitro release methods used to investigate nanocarriers intended for dermal application

In vitro drug release measurement is one of the most important methods used to assess the quality of a nanocarrier and estimate it́s in vivo performance. Different in vitro drug release methods have been used to investigate the drug release from nanocarriers, however, little information is available with regard to a comparison of these methods (e.g. discriminative power, reproducibility). Thus, drug release from four nanocarriers (nanocrystals, lipid nanoparticles, Eudragit^® RS and ethyl cellulose nanoparticles) was investigated under sink and non-sink conditions with three drug release methods: an in situ method using Sirius^® inForm and two in vitro methods using dialysis bags and Franz diffusion cells. Dexamethasone was used as the model drug. The in situ measurement was a simple and fast method but not adequately discriminating because of a too rapid drug dissolution/release. Franz diffusion cells and dialysis bags were in most cases discriminative for the different nanocarriers with the drug dissolution/release being in the order of nanocrystals>Eudragit^® RS nanoparticles>lipid nanoparticles>ethyl cellulose nanoparticles. Drug release experiments with Franz diffusion cells had the highest reproducibility. The Franz diffusion cells could also be easily used with semisolid dosage forms.

A Review: Pharmaceutical and Pharmacokinetic Aspect of Nanocrystalline Suspensions

Nanocrystals have emerged as a potential formulation strategy to eliminate the bioavailability-related problems by enhancing the initial dissolution rate and moderately super-saturating the thermodynamic solubility. This review contains an in-depth knowledge of, the processing method for formulation, an accurate quantitative assessment of the solubility and dissolution rates and their correlation to observe pharmacokinetic data. Poor aqueous solubility is considered the major hurdle in the development of pharmaceutical compounds. Because of a lack of understanding with regard to the change in the thermodynamic and kinetic properties (i.e., solubility and dissolution rate) upon nanosizing, we critically reviewed the literatures for solubility determination to understand the significance and accuracy of the implemented analytical method. In the latter part, we reviewed reports that have quantitatively studied the effect of the particle size and the surface area change on the initial dissolution rate enhancement using alternative approaches besides the sink condition dissolution. The lack of an apparent relationship between the dissolution rate enhancement and the observed bioavailability are discussed by reviewing the reported in vivo data on animal models along with the particle size and food effect. The review will provide comprehensive information to the pharmaceutical scientist in the area of nanoparticulate drug delivery.

α-Tocopherol succinate improves encapsulation and anticancer activity of doxorubicin loaded in solid lipid nanoparticles

This work aimed to develop solid lipid nanoparticles (SLN) co-loaded with doxorubicin and α-tocopheryl succinate (TS), a succinic acid ester of α-tocopherol that exhibits anticancer actions, evaluating the influence of TS on drug encapsulation efficiency. The SLN were characterized for size, zeta potential, entrapment efficiency (EE), and drug release. Studies of in vitro anticancer activity were also conducted. The EE was significantly improved from 30 ± 1% to 96 ± 2% for SLN without and with TS at 0.4%, respectively. In contrast, a reduction in particle size from 298 ± 1 to 79 ± 1 nm was observed for SLN without and with TS respectively. The doxorubicin release data show that SLN provide a controlled drug release. The in vitro studies showed higher cytotoxicity for doxorubicin-TS-loaded SLN than for free doxorubicin in breast cancer cells. These findings suggest that TS-doxorubicin-loaded SLN is a promising alternative for the treatment of cancer.

A Review of In Vitro Drug Release Test Methods for Nano-Sized Dosage Forms

This review summarizes the methods used to study real-time (37°C) drug release from nanoparticulate drug delivery systems and establish an IVIVC. Since no compendial standards exist, drug release is currently assessed using a variety of methods including sample and separate (SS), continuous flow (CF), dialysis membrane (DM) methods, and a combination thereof, as well as novel techniques like voltametry and turbidimetry. This review describes the principle of each method along with their advantages and disadvantages, including challenges with set-up and sampling. The SS method allows direct measurement of drug release with simple set-up requirements, but sampling is cumbersome. With the CF method, sampling is straightforward but the set-up is time consuming. Set-up as well as sampling is easier with the DM, but it may not be suitable for drugs that bind to the membrane. Novel methods offer the possibility of real-time drug release measurement but may be restricted to certain types of drugs. Of these methods, Level A IVIVCs have been obtained with dialysis, alone or in combination with the sample and separate technique. Future efforts should focus on developing mathematical models that describe drug release mechanisms as well as facilitate formulation development of nano-sized dosage forms.

Evaluating the potential of cubosomal nanoparticles for oral delivery of amphotericin B in treating fungal infection

The oral administration of amphotericin B (AmB) has a major drawback of poor bioavailability. The aim of this study was to investigate the potential of glyceryl monoolein (GMO) cubosomes as lipid nanocarriers to improve the oral efficacy of AmB. Antifungal efficacy was determined in vivo in rats after oral administration, to investigate its therapeutic use. The human colon adenocarcinoma cell line (Caco-2) was used in vitro to evaluate transport across a model of the intestinal barrier. In vivo antifungal results showed that AmB, loaded in GMO cubosomes, could significantly enhance oral efficacy, compared against Fungizone®, and that during a 2 day course of dosage 10 mg/kg the drug reached effective therapeutic concentrations in renal tissue for treating fungal infections. In the Caco-2 transport studies, GMO cubosomes resulted in a significantly larger amount of AmB being transported into Caco-2 cells, via both clathrin- and caveolae-mediated endocytosis, but not macropinocytosis. These results suggest that GMO cubosomes, as lipid nanovectors, could facilitate the oral delivery of AmB.

Layer-by-layer polymer coating on discrete particles of cubic lyotropic liquid crystalline dispersions (cubosomes)

Cubic phase lyotropic liquid crystalline colloidal dispersions (cubosomes) were surface-modified with seven polyelectrolyte layers using a layer-by-layer (LbL) approach. The first layer consisted of a copolymer synthesized from methacrylic acid and oleoyl methacrylate for enhanced incorporation within the bilayer of the cubic nanostructure. Six additional layers of poly(L-lysine) and poly(methacrylic acid) were then sequentially added, followed by a washing procedure to remove polymer aggregates from the soft matter particles. Polymer buildup was monitored via microelectrophoresis, dynamic light scattering, and small-angle X-ray scattering. Polymer-coated cubosomes were observed with cryo-transmission electron microscopy. A potential application of the modified nanostructured particles presented in this study is to reduce the burst-release effect associated with drug-loaded cubosomes. The effectiveness of this approach was demonstrated through loading and release results from a model hydrophilic small molecule (fluorescein).

Optimized loading and sustained release of hydrophilic proteins from internally nanostructured particles

In this study, we demonstrate that emulsified microemulsions and micellar cubosomes are suitable as sustained delivery vehicles for water-soluble proteins. Through structural modifications, the loading efficiency of two model proteins, namely bovine serum albumin (BSA) and cytochrome c could be remarkably increased. A procedure for preparing these particles loaded with optimized amounts of sensitive substances is presented. Loading and dispersion at low temperatures is performed in two successive steps. First, a water-in-oil microemulsion is loaded with the proteins. Subsequently, this phase is dispersed in water resulting in particles with microemulsion and micellar cubic internal structure and a size of approximately 620 nm. This two-step method ensures optimal loading of the particles with the proteins. These nanostructured particles are able to sustain the release of the water-soluble BSA and cytochrome c. Within one day, less than 10% of BSA and 15% of cytochrome c are released. The release rate of cytochrome c is influenced by the nanostructure of the particles.

Development of a new method to assess nanocrystal dissolution based on light scattering

PURPOSE

Nanocrystals exhibit enhanced dissolution rates and can effectively increase the bioavailability of poorly water soluble drug substances. However, methods for in vitro characterization of dissolution are unavailable. The objective of this study was to develop an in situ noninvasive analytical method to measure dissolution of crystalline nanosuspensions based on light scattering.

METHODS

Fenofibrate nanosuspensions were prepared by wet media milling. Their solubilities and dissolution profiles in simulated gastric fluid supplemented with 0.1% Tween(®) 80 were measured in a small scale setup with an instrument for dynamic light scattering and the intensity of scattered light as readout parameter.

RESULTS

A good correlation was achieved between the dissolution profile of a nanosuspension measured in the light scattering setup and a conventional dissolution experiment. Nanosuspensions of 120-270 nm size could be distinguished by the light scattering method. The suspensions dissolved within 1.9-12.3 min. Over a concentration range of 40-87% of the solubility dissolution profiles of a nanosuspension with 140 nm were monitored and the determined total dissolution times were in good agreement with the Noyes-Whitney dissolution model.

CONCLUSIONS

A noninvasive, sensitive and reproducible method is presented to assess nanocrystal dissolution. In situ measurements based on light scattering allow a straightforward experimental setup with high temporal resolution.

Drug release from nanomedicines: Selection of appropriate encapsulation and release methodology

The characterization of encapsulation efficiency and in vitro drug release from nanoparticle-based formulations often requires the separation of nanoparticles from unencapsulated drug. Inefficient separation of nanoparticles from the medium in which they are dispersed can lead to inaccurate estimates of encapsulation efficiency and drug release. This study establishes dynamic light scattering as a simple method for substantiation of the effectiveness of the separation process. Colistin-loaded liposomes, as an exemplar nano-sized delivery particle, were diluted to construct a calibration curve relating the amount of light scattering to liposome concentration. Dynamic light scattering revealed that, in the case of ultracentrifugation and centrifugal ultrafiltration, approximately 2.9% of the total liposomes remained in supernatants or filtrates, respectively. In comparison, filtrates obtained using pressure ultrafiltration contained less than 0.002% of the total liposomes from the formulation. Subsequent release studies using dialysis misleadingly implied a slow release of colistin over >48 h. In contrast, pressure ultrafiltration revealed immediate equilibration to the equilibrium distribution of colistin between the liposome and aqueous phases upon dilution. Pressure ultrafiltration is therefore recommended as the optimal method of choice for studying release kinetics of drug from nanomedicine carriers.

Lipid nanoparticles for the delivery of poorly water-soluble drugs

OBJECTIVES

This review discusses important aspects of lipid nanoparticles such as colloidal lipid emulsions and, in particular, solid lipid nanoparticles as carrier systems for poorly water-soluble drugs, with a main focus on the parenteral and peroral use of these carriers.

KEY FINDINGS

A short historical background of the development of colloidal lipid emulsions and solid lipid nanoparticles is provided and their similarities and differences are highlighted. With regard to drug incorporation, parameters such as the chemical nature of the particle matrix and the physicochemical nature of the drug, effects of drug partition and the role of the particle interface are discussed. Since, because of the crystalline nature of their lipid core, solid lipid nanoparticles display some additional important features compared to emulsions, their specificities are introduced in more detail. This mainly includes their solid state behaviour (crystallinity, polymorphism and thermal behaviour) and the consequences of their usually non-spherical particle shape. Since lipid nanoemulsions and -suspensions are also considered as potential means to alter the pharmacokinetics of incorporated drug substances, some underlying basic considerations, in particular concerning the drug-release behaviour of such lipid nanodispersions on dilution, are addressed as well.

CONCLUSIONS

Colloidal lipid emulsions and solid lipid nanoparticles are interesting options for the delivery of poorly water-soluble drug substances. Their specific physicochemical properties need, however, to be carefully considered to provide a rational basis for their development into effective carrier systems for a given delivery task.

Preparation of phytantriol cubosomes by solvent precursor dilution for the delivery of protein vaccines

Different delivery strategies to improve the immunogenicity of peptide/protein-based vaccines are currently under investigation. In this study, the preparation and physicochemical characterisation of cubosomes, a novel lipid-based particulate system currently being explored for vaccine delivery, was investigated. Cubosomes were prepared from a liquid precursor mixture containing phytantriol or glycerylmonooleate (GMO), F127 for particle stabilisation, and a hydrotrope (ethanol or polyethylene glycol (PEG(200)) or propylene glycol (PG)). Several liquid precursors were prepared, and the effect of varying the concentrations of F127 and the hydrotrope on cubosome formation was investigated. Formulations were prepared by fragmentation for comparison. The model protein ovalbumin (Ova) was also entrapped within selected formulations. Submicron-sized particles (180-300 nm) were formed spontaneously upon dilution of the liquid precursors, circumventing the need for the preformed cubic phase used in traditional fragmentation-based methods. The nanostructure of the phytantriol dispersions was determined to be cubic phase using SAXS whilst GMO dispersions had a reverse hexagonal nanostructure coexisting with cubic phase. The greatest entrapment of Ova was within phytantriol cubosomes prepared from liquid precursors. Release of Ova from the various formulations was sustained; however, release was significantly faster and the extent of release was greater from fragmented dispersions compared to liquid precursor formulations. Taken together, these results suggest that phytantriol cubosomes can be prepared using liquid precursors and that it is a suitable alternative to GMO. Furthermore, the high entrapment and the slow release of Ova in vitro highlight the potential of phytantriol cubosomes prepared using liquid precursors as a novel vaccine delivery system.

Flow cytometry as a new approach to investigate drug transfer between lipid particles

Lipid nanoparticles and liposomal carrier systems are of growing interest for intravenous drug delivery due to their biocompatibility and targetability. It is, however, difficult to investigate their release behavior for lipophilic drugs under physiological conditions. This study describes a novel flow cytometric method studying drug transfer from such carrier systems to particles simulating physiological receptor sites. For this purpose, liquid and solid trimyristin nanoparticles or soybean phospholipid liposomes were loaded with the lipophilic fluorescent substances Nile red, temoporfin, and DiI. The transfer of these model drugs to large emulsion droplets was examined by flow cytometry. Transfer of DiI to differently sized acceptor emulsions was also monitored by separating donor and acceptor particles using ultracentrifugation. Flow cytometry revealed a completion of transfer within a few minutes for Nile red and temoporfin at considerable amounts of transferred dye. In contrast, the highly lipophilic DiI transferred over a period of weeks only for a small percentage of the dye. Ultracentrifugation results confirmed this for DiI and indicated a dependence of transfer characteristics on the acceptor surface area. Nile red transfer into a bulk oil phase as alternative acceptor system was also very slow. Flow cytometry seems to be well suited to study the intrinsic transfer of fluorescent lipophilic substances, as no kinetic hindrances like dialysis bags nor separation steps are required. Additional detailed experiments will, however, be necessary to elucidate the prevalent transfer mechanisms completely.

Characterization and potential applications of nanostructured aqueous dispersions

The present article highlights recent advances and current status in the characterization and the utilization of nanostructured aqueous dispersions in which the submicron-sized dispersed particles envelope a distinctive well-defined self-assembled interior. The scope of this review covers dispersions of both inverted-type liquid-crystalline particles (cubosomes, hexosomes, micellar cubosomes, and sponge phases), and microemulsion droplets (emulsified microemulsions, EMEs). Recent investigations that have attempted to shed light on the characterization and the control of confined nanostructures of aqueous dispersions are surveyed, as these nanoobjects are attractive for various pharmaceutical and food applications. The focus has been placed on three main subjects: (1) our findings on the formation of EMEs and the modulation of the internal nanostructure, exploring how variations in temperature, oil content, and lipid composition significantly affect the confined nanostructures; (2) recent developments in the field of electron microscopy: using the tilt-angle cryo-TEM method or cryo-field emission scanning electron microscopy (cryo-FESEM) for observing the three dimensional (3D) morphology of non-lamellar liquid-crystalline nanostructured particles (cubosome and hexosome particles); and (3) recent studies on the utilization of nanostructured dispersions as drug nanocarriers.