Dissolution studies of poorly soluble drug nanosuspensions in non-sink conditions.

Sink conditions used in dissolution tests lead to rapid dissolution rates for nanosuspensions, causing difficulties in discriminating dissolution profiles between different formulations. Here, non-sink conditions were studied for the dissolution testing of poorly water-soluble drug nanosuspensions. A mathematical model for polydispersed particles was established to clarify dissolution mechanisms. The dissolution of nanosuspensions with either a monomodal or bimodal size distribution was simulated. In the experimental part, three different particle sizes of indomethacin nanosuspensions were prepared by the wet milling technique. The effects of the dissolution medium pH and agitation speed on dissolution rate were investigated. The dissolution profiles in sink and non-sink conditions were obtained by changing the ratio of sample amount to the saturation solubility. The results of the simulations and experiments indicated that when the sample amount was increased to the saturation solubility of drug, the slowest dissolution rate and the best discriminating dissolution profiles were obtained. Using sink conditions or too high amount of the sample will increase the dissolution rate and weaken the discrimination between dissolution profiles. Furthermore, the low solubility by choosing a proper pH of the dissolution medium was helpful in getting discriminating dissolution profiles, whereas the agitation speed appeared to have little influence on the dissolution profiles. This discriminatory method is simple to perform and can be potentially used in any nanoproduct development and quality control studies.

Volume-averaged SAR in adult and child head models when using mobile phones: a computational study with detailed CAD-based models of commercial mobile phones.

Previous studies comparing SAR difference in the head of children and adults used highly simplified generic models or half-wave dipole antennas. The objective of this study was to investigate the SAR difference in the head of children and adults using realistic EMF sources based on CAD models of commercial mobile phones. Four MRI-based head phantoms were used in the study. CAD models of Nokia 8310 and 6630 mobile phones were used as exposure sources. Commercially available FDTD software was used for the SAR calculations. SAR values were simulated at frequencies 900 MHz and 1747 MHz for Nokia 8310, and 900 MHz, 1747 MHz and 1950 MHz for Nokia 6630. The main finding of this study was that the SAR distribution/variation in the head models highly depends on the structure of the antenna and phone model, which suggests that the type of the exposure source is the main parameter in EMF exposure studies to be focused on. Although the previous findings regarding significant role of the anatomy of the head, phone position, frequency, local tissue inhomogeneity and tissue composition specifically in the exposed area on SAR difference were confirmed, the SAR values and SAR distributions caused by generic source models cannot be extrapolated to the real device exposures. The general conclusion is that from a volume averaged SAR point of view, no systematic differences between child and adult heads were found.

¹8F-labeled modified porous silicon particles for investigation of drug delivery carrier distribution in vivo with positron emission tomography.

Because of its biocompatibility and ability to accommodate a variety of payloads from poorly soluble drugs to biomolecules, porous silicon (PSi) is a lucrative material for the development of carriers for particle-mediated drug delivery. We report a successful direct one-step (18)F-radiolabeling of three types of PSi microparticles, thermally hydrocarbonized THCPSi, thermally oxidized TOPSi, and thermally carbonized TCPSi for the investigation of their biodistribution in vivo with positron emission tomography as part of their evaluation as carriers for particle-mediated drug delivery. FTIR and XPS characterization of the PSi materials after carrier-added (18)F/(19)F-radiolabeling reveals that depending on the material the (18)F-labeling is likely to be accomplished either by substitution for surface silyl hydrogen or silyl fluoride or by nucleophilic attack of (18)F(-) to Si-O-Si bridges. With the selected (18)F-radiolabeling method, good to excellent in vitro radiolabel stability in simulated gastric and intestinal fluids and in plasma is achieved for all the particle types studied. Finally, a preliminary evaluation of (18)F-THCPSi microparticle biodistribution in the rat gastrointestinal tract after oral administration is reported, illustrating the utility of using (18)F-radiolabeled PSi as imaging probes for PSi-based drug delivery carrier distribution in vivo.

Physicochemical stability of high indomethacin payload ordered mesoporous silica MCM-41 and SBA-15 microparticles.

Stability of high indomethacin (IMC) content formulations based on ordered mesoporous silica MCM-41 and SBA-15 materials was studied before and after a 3 month storage in stressed conditions (30°C/56% RH). Overall, the physical stability of the samples was found satisfactory after the storage. However, some issues with the chemical stability were noted, especially with the MCM-41 based samples. The stability issues were evident from the decreased HPLC loading degrees of the drug after stressing as well as from the observed extra peaks in the HPLC chromatograms of the drug in the stressed samples. Drug release from the mesoporous formulations before stressing was rapid at pH 1.2 in comparison to bulk crystalline IMC. The release profiles also remained similar after stressing. Even faster and close to complete IMC release was achieved when the pH was raised from 1.2 to 6.8. To our knowledge, this is the first report of chemical stability issues of drugs in mesoporous silica drug formulations. The present results encourage further study of the factors affecting the chemical stability of drugs in mesoporous silica MCM-41 and SBA-15 formulations in order to realize their potential in oral drug delivery.

Comparison of mesoporous silicon and non-ordered mesoporous silica materials as drug carriers for itraconazole.

Mesoporous materials have an ability to enhance dissolution properties of poorly soluble drugs. In this study, different mesoporous silicon (thermally oxidized and thermally carbonized) and non-ordered mesoporous silica (Syloid AL-1 and 244) microparticles were compared as drug carriers for a hydrophobic drug, itraconazole (ITZ). Different surface chemistries pore volumes, surface areas, and particle sizes were selected to evaluate the structural effect of the particles on the drug loading degree and on the dissolution behavior of the drug at pH 1.2. The results showed that the loaded ITZ was apparently in amorphous form, and that the loading process did not change the chemical structure/morphology of the particles' surface. Incorporation of ITZ in both microparticles enhanced the solubility and dissolution rate of the drug, compared to the pure crystalline drug. Importantly, the physicochemical properties of the particles and the loading procedure were shown to have an effect on the drug loading efficiency and drug release kinetics. After storage under stressed conditions (3 months at 40 °C and 70% RH), the loaded silica gel particles showed practically similar dissolution profiles as before the storage. This was not the case with the loaded mesoporous silicon particles due to the almost complete chemical degradation of ITZ after storage.

Kinetics of lactose and rhamnose oxidation over supported metal catalysts.

Several mono- and bimetallic Pd, Pt, Rh and Ru supported on alumina and active carbon catalysts were characterized by CO chemisorption, nitrogen adsorption, XPS and XRD and acidity titrations were performed for active carbon supported catalysts. These catalysts were tested in oxidation of two sugars, namely lactose and rhamnose, at 60 °C and at 70 °C under slightly alkaline conditions (pH 8) with molecular oxygen. The results revealed that there is an optimum metal particle size in a range of 3-10 nm giving the highest initial TOFs for both oxidations. Furthermore, the catalytic activities and conversions were related to other catalyst properties, such as the type and amount of promoters and the presence of different phases. In situ catalyst potential measurements revealed that there is an inverse correlation between the increase of catalyst potential as a function of sugar conversion and the catalyst activity after prolonged reaction times. This method is a valuable tool for in situ characterization of catalysts correlating well with their activities.

Drug delivery formulations of ordered and nonordered mesoporous silica: comparison of three drug loading methods.

A poorly soluble model drug, indomethacin (IMC), was loaded into two types of silica particles using three different loading methods. The loading efficiency and the extent/rate of drug release were evaluated. Widely used equipment in pharmaceutical laboratories, rotavapor and fluid bed, were used in the loading. The porous materials used were ordered mesoporous silica MCM-41 and nonordered silica gel Syloid 244 FP EU. The materials differ both in their pore properties and particle sizes. Tablets were successfully compressed from the IMC-loaded particles. Mechanical stability of the porous structures was studied with XRPD and nitrogen sorption after tableting and drug release was evaluated at pH 5.5 before and after tableting. The release of the poorly soluble IMC was faster from the Syloid than from the MCM-41, presumably due to the larger pore size and smaller particle size. Loading of IMC into the MCM-41 microparticles improved the drug dissolution, and blending the microparticles with pharmaceutical excipients improved the IMC release even further. The fast release was also maintained after tableting. Loading of IMC into the Syloid particles alone was sufficient to produce similar IMC release profiles, as in the case of MCM-41 with the excipients.

Similarly derived and cultured hESC lines show variation in their developmental potential towards neuronal cells in long-term culture.

BACKGROUND: Human embryonic stem cells (hESCs) can differentiate into any human cell type, including CNS cells, and thus have high potential in regenerative medicine. Several protocols exist for neuronal differentiation of hESCs, which do not necessarily work for all hESC lines. MATERIALS & METHODS: We tested the differentiation capacity of four similarly derived and cultured hESC lines (HS181, HS360, HS362 and HS401) in suspension culture in relatively simple neural differentiation medium for up to 20 weeks. RESULTS: All the hESC lines differentiated into neuronal cells, but in a line-dependent manner. Using our method, the HS181- and HS360-derived neurospheres differentiated in vitro into pure neuronal cell populations within 6 weeks, whereas HS362 and HS401 reached their peak of differentiation in 12 weeks, but never produced pure neuronal cell populations using the present method. The withdrawal of FGF from suspension culture increased the in vitro differentiation potential. The hESC-derived neurospheres formed functional neuronal networks when replated on a microelectrode array and responded as expected to pharmacologic modulation. CONCLUSION: Simple neurosphere culture is a suitable method for producing hESC-derived neuronal cells that can form functional neuronal networks from a number of hESC lines. The variation in the differentiation potential of hESC lines into neuronal cells must be carefully considered by those comparing various differentiation methods and designing transplantation therapies for neuronal disorders.

Cytotoxicity study of ordered mesoporous silica MCM-41 and SBA-15 microparticles on Caco-2 cells.

Cytotoxicity of ordered mesoporous silica MCM-41 and SBA-15 microparticles (fractions between 1 and 160 microm) was determined in vitro on undifferentiated human colon carcinoma (Caco-2) cell line, considering the feasibility of using these silica-based materials in oral drug formulations. The cellular endpoints employed for assessing the effects of the MCM-41 and SBA-15 microparticles on Caco-2 were: (1) cell membrane integrity by monitoring live-cell protease activity (AFC) and by employing the flow cytometry method; (2) metabolic activity by monitoring total ATP content via luminescence assay; (3) activity of apoptotic effectors by caspase-3/7 activity assay. The generation of reactive oxygen species (ROS) was also followed, specifically the hydrogen peroxide (H(2)O(2)) and the superoxide radical (O(2)(-)). MCM-41 and SBA-15 microparticles caused cytotoxic effects on the Caco-2 cells, at most tested concentrations (0.2-14 mg/ml) and incubation times (3 and 24h). The effects on the cells included weakened cell membrane integrity, diminished cell metabolism and increased apoptotic signalling. The root cause for the cytotoxicity was heightened production of reactive oxygen species (ROS), especially the formation of the superoxide radical O(2)(-) already after 3h incubation with threshold dose 1mg/ml, apparently overwhelming the antioxidant defences and causing mitochondrial dysfunction, hence increasing the apoptotic signalling.

In vitro cytotoxicity of porous silicon microparticles: effect of the particle concentration, surface chemistry and size.

We report here the in vitro cytotoxicity of mesoporous silicon (PSi) microparticles on the Caco-2 cells as a function of particle size fractions (1.2-75 microm), particle concentration (0.2-4 mg ml(-1)) and incubation times (3, 11 and 24 h). The particle size (smaller PSi particles showed higher cytotoxicity) and the surface chemistry treatment of the PSi microparticles were considered to be the key factors regarding the toxicity aspects. These effects were significant after the 11 and 24 h exposure times, and were explained by cell-particle interactions involving mitochondrial disruption resulting from ATP depletion and reactive oxygen species production induced by the PSi surface. These events further induced an increase in cell apoptosis and consequent cell damage and cell death in a dose-dependent manner and as a function of the PSi particle size. These effects were, however, less pronounced with thermally oxidized PSi particles. Under the experimental conditions tested and at particle sizes >25 microm, the non-toxic threshold concentration for thermally hydrocarbonized and carbonized PSi particles was <2 mg ml(-1), and for thermally oxidized PSi microparticles was <4 mg ml(-1).

Human embryonic stem cell-derived neuronal cells form spontaneously active neuronal networks in vitro.

The production of functional human embryonic stem cell (hESC)-derived neuronal cells is critical for the application of hESCs in treating neurodegenerative disorders. To study the potential functionality of hESC-derived neurons, we cultured and monitored the development of hESC-derived neuronal networks on microelectrode arrays. Immunocytochemical studies revealed that these networks were positive for the neuronal marker proteins beta-tubulin(III) and microtubule-associated protein 2 (MAP-2). The hESC-derived neuronal networks were spontaneously active and exhibited a multitude of electrical impulse firing patterns. Synchronous bursts of electrical activity similar to those reported for hippocampal neurons and rodent embryonic stem cell-derived neuronal networks were recorded from the differentiated cultures until up to 4 months. The dependence of the observed neuronal network activity on sodium ion channels was examined using tetrodotoxin (TTX). Antagonists for the glutamate receptors NMDA [D(-)-2-amino-5-phosphonopentanoic acid] and AMPA/kainate [6-cyano-7-nitroquinoxaline-2,3-dione], and for GABAA receptors [(-)-bicuculline methiodide] modulated the spontaneous electrical activity, indicating that pharmacologically susceptible neuronal networks with functional synapses had been generated. The findings indicate that hESC-derived neuronal cells can generate spontaneously active networks with synchronous communication in vitro, and are therefore suitable for use in developmental and drug screening studies, as well as for regenerative medicine.

Failure of MTT as a toxicity testing agent for mesoporous silicon microparticles.

In this work, it is shown that the common toxicity indicator, MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide), will fail to predict the toxicity of porous silicon (PSi) microparticles. This is due to the spontaneous redox reactions where the MTT is reduced and the PSi particle surfaces are oxidized simultaneously. MTT was shown to even react with thermally oxidized and carbonized forms of PSi particles, although the treatment did give an enhanced protection against the unwanted reactions as compared to as-anodized PSi particles. The observed levels of cellular viability with the MTT assay were much higher than expected in the presence of Caco-2 cells, even considering the spontaneous reduction of MTT at PSi surfaces. The results indicate that the redox reaction is further enhanced inside living cells. Thus, we recommend that MTT should not be used to test the cytotoxicity of drug formulations containing PSi microparticles. The study also shows that since PSi particles are capable of reducing the MTT, they will also be able to reduce other species as well. This should be taken into account when considering future applications for the porous silicon particles. The completely oxidized SiO2 particles (MCM-41 and SBA-15) were shown to work as expected with the MTT assay and showed no inherent oxidation/reduction.

Crystal structure changes of gamma-cyclodextrin after the SEDS process in supercritical carbon dioxide affect the dissolution rate of complexed budesonide.

PURPOSE: The present study describes the crystal structure changes of gamma-cyclodextrin (gamma-CD) during the solution enhanced dispersion by supercritical fluids (SEDS) process and its effect on dissolution behaviour of complexed budesonide. MATERIALS AND METHODS: gamma-CD solution (10 mg/ml in 50% ethanol) was pumped together with supercritical carbon dioxide through a coaxial nozzle with or without a model drug, budesonide (3.3 mg/ml). The processing conditions were 100 b and 40, 60 or 80 degrees C. gamma-CD powders were characterised before and after vacuum-drying (2-3 days at RT) with XRPD, SEM and NMR. Budesonide/gamma-CD complexation was confirmed with DSC and XRPD. The dissolution behaviour of complexed budesonide was determined in aqueous solution (1% gamma-CD, 37 degrees C, 100 rpm). RESULTS: During the SEDS process (100 b, 40 and 60 degrees C), gamma-CD and budesonide/gamma-CD complexes crystallized in a tetragonal channel-type form. The vacuum-drying transformed crystalline gamma-CD into amorphous form while the complexes underwent a tetragonal-to-hexagonal phase transition. The increase in the processing temperature decreased the crystallinity of gamma-CD. At 80 degrees C, amorphous gamma-CD was obtained while the complexes crystallized in a hexagonal channel-type form. The dissolution behaviour of budesonide/gamma-CD complexes was dependent on their crystal structure: the tetragonal form dissolved faster than the hexagonal form. CONCLUSIONS: The crystal structure of gamma-CD and subsequently, the dissolution rate of complexed budesonide, can be modified with the processing conditions.

Enhanced in vitro permeation of furosemide loaded into thermally carbonized mesoporous silicon (TCPSi) microparticles.

The combined release and permeation behavior of furosemide loaded into thermally carbonized mesoporous silicon (TCPSi) microparticles was studied in order to evaluate the potential of TCPSi-loading to improve permeation of furosemide, a BCS class IV compound. Permeation was studied across Caco-2 monolayers at pH 5.5, 6.8 and 7.4 from drug solutions and TCPSi particles. TCPSi-loaded furosemide (39% w/w) exhibited improved dissolution from the microparticles with greatly diminished pH dependence. At pH 5.5, where furosemide solubility restricted the amount that could be dissolved in the control solution to less than 30% of the dose contained in the TCPSi particles, the flux of TCPSi-loaded furosemide across Caco-2 monolayers was over fivefold compared to pre-dissolved furosemide. The improved permeation could be confirmed also from dose-corrected (% dose-permeated) results. At pH 6.8 and pH 7.4, where corresponding doses could be used in control solutions, more than fourfold permeability values were obtained with TCPSi-loaded furosemide. Effects on transepithelial electrical resistance (TEER) and mannitol permeability were monitored and suggest that monolayer integrity was not compromised by the drug-loaded TCPSi microparticles. The improved permeation observed from furosemide-loaded TCPSi particles suggests that the high local concentrations provided by the enhanced dissolution properties of TCPSi-loaded furosemide could prove beneficial for absorption.

Preparation of budesonide/gamma-cyclodextrin complexes in supercritical fluids with a novel SEDS method.

The aim was to investigate if solid drug/cyclodextrin complexes could be produced in a single-step process with a solution enhanced dispersion by supercritical fluids (SEDS) method. Budesonide and gamma-cyclodextrin (CD) solutions (50% or 99.5% ethanol) were pumped from the same (conventional method) or separate (modified method) containers together with supercritical carbon dioxide through a coaxial nozzle into a particle formation chamber. The pressure was maintained at 100, 150 or 200 bar with a temperature of 40, 60 or 80 degrees C. SEDS-processed powders were characterised with HPLC, DSC and XRPD for budesonide content, complexation and crystallinity. The budesonide dissolution rate was determined in 1% gamma-CD aqueous solution. Solid, white budesonide/gamma-CD complex particles were formed using the conventional and modified SEDS processes. The complexation efficiency was dependent on the processing conditions. For example, with the conventional method (100 bar, 60 degrees C) the yield of the powder was 65+/-12% with 0.14+/-0.02 mg budesonide/mg powder, corresponding to 1:2 drug:CD molar ratio. The dissolution rate of this complexed budesonide (93+/-2% after 15 min) was markedly higher compared to unprocessed micronised budesonide (41+/-10%) and SEDS-processed budesonide without CD (61+/-3%). As a conclusion, SEDS is a novel method to produce solid drug/CD complexes in a single-step process.

Characterization of the preferred orientation of delta-mannitol crystallites in tablets.

The crystallographic texture, i.e. the preferred orientation of crystallites of delta-mannitol samples, has been experimentally determined by pole figure analysis. The pole figures were measured with an X-ray diffraction texture goniometer. It was found that already the uncompressed delta-mannitol powder sample was slightly texturized so that the (0 2 0) plane was parallel to the upper surface of the sample. The degree of preferred orientation was found to significantly increase when the powder was compressed to a tablet with the minimum (74MPa) compression pressure. Nevertheless, the direction of the texture remained parallel to the tablet surface. Maximum compression (740MPa) did not increase the degree of preferred orientation further. The compression time (0 or 60s) was not found to noticeably affect the strength or direction of the texture. The extent of the texture inside the tablet was determined with a tablet surface grinding experiment. The degree of preferred orientation was found to decrease under the surface while the orientation remained the same. The results were confirmed with orientation distribution function (ODF) calculations.