Plasmid DNA is protected against ultrasonic cavitation-induced damage when complexed to cationic liposomes

Cationic liposomes bound to plasmid DNA are currently used for in vitro and in vivo gene therapy applications, but such complexes readily form large, heterogeneous aggregates that are not appropriate for pharmaceutical development. More importantly, size heterogeneity makes studies focused on optimizing gene transfer to cells difficult to conduct or understand. For this reason we have evaluated the effect of microprobe sonication on these complexes in an effort to achieve process-controlled size homogeneity. Complexes were prepared using a 7.2 kb reporter plasmid and the following liposomal lipid combinations: DDAB/DOPE (50:50 mol %), DDAB/DOPE/PEG-PE (50:45:5 mol %), DDAB/EPC (50:50 mol %), DDAB/EPC/PEG-PE (50:45:5, 50:40:10, 50:35:15 mol %), DODAC/DOPE (50:50 mol %), and DODAC/EPC (50:50 mol %) (DDAB, dimethyldioctadecylammonium bromide; DOPE, dioleoylphosphatidylethanolamine; PEG-PE, monomethoxypolyethylene glycol2000 succinate- distearoylphosphatidylethanolamine; EPC, egg phosphatidylcholine; DODAC, dioleoyldimethylammonium chloride). The influence of complex composition and lipid:DNA ratio was evaluated. Particle size was determined before and after complexation and again after sonication using the quasi-elastic light scattering technique. DNA integrity was assessed via agarose gel electrophoresis. Finally, gene transfection was evaluated using CHO cells that were transfected in vitro with sonicated and unsonicated complexes. It is established in this study that size reduction can occur, but this is dependent on cationic and neutral lipid composition and, in some cases, lipid:DNA ratio. Surprisingly, the process of sonication leaves a significant percentage of the plasmid DNA intact and capable of in vitro transfection. This study shows that plasmid DNA can be protected from damage due to sonication by liposome complex formation. This may indicate that more common pharmaceutical methods for size reduction which subject particles to mechanical stress may be applicable in preparation of liposome/DNA formulations for in vivo application.     

The role of colloid chemistry in modeling deep bed liquid filtration

From mass balance on the suspension and filter and a charge balance on the filter, a set of hyperbolic partial differential equations is derived which describes how the suspension concentration, surface charges of the filter and particles, porosity of the filter, and the pressure drop vary with filter depth and time. These equations include a local deposition term which is evaluated by considering transport of the suspension particles to the filter particles by Brownian diffusion, interception, and sedimentation. The effect of the surface forces due to electrical double layer and van der Waals interactions was taken into account by treating the surface of the filter particles as possessing first order intermediate reaction kinetics, for which the rate constant is a function of the stability ratio of colloid chemistry.The governing equations were solved numerically, and the results compared with experimental data for unflocculated particles.The proposed filtration model is an advance over present models in that it contains no empirical factors which must be evaluated from filter runs and the effects of surfactants, pH, and ionic strength are accounted for.     

Critical heat flux of a two-phase closed thermosyphon with fins

Journal of Mechanical Science and Technology - The critical heat fluxes (CHFs) of two-phase closed thermosyphons with and without fins were studied. The thermosyphons were fabricated using...     

Application of a simple enthalpy‐based pyrolysis model in numerical simulations of pyrolysis of charring materials

A new, simple pyrolysis model for charring materials is applied to several numerical and experimental test cases with variable externally imposed heat fluxes. The model is based on enthalpy. A piecewise linear temperature field representation is adopted, in combination with an estimate for the pyrolysis front position. Chemical kinetics are not accounted for: the pyrolysis process takes place in an infinitely thin front, at the ‘pyrolysis temperature’. The evolution in time of pyrolysis gases mass flow rates and surface temperatures is discussed. The presented model is able to reproduce numerical reference results, which were obtained with the more complex moving mesh model. It performs better than the integral model. We illustrate good agreement with numerical reference results for variable thickness and boundary conditions. This reveals that the model provides good results for the entire range of thermally thin and thermally thick materials. It also shows that possible interruption of the pyrolysis process, due to excessive heat losses, is automatically predicted with the present approach. Finally, an experimental test case is considered. Copyright © 2009 John Wiley & Sons, Ltd.     

Analysis and evaluation of permeability techniques for characterizing fine particles Part I. Diffusion and flow through porous media

The specific surface area and particle size can be deduced with speed and simplicity from appropriate measurements and calculations of fluid flow and diffusion in porous media. The interdependence of these two processes is developed in a series of two articles.In Part I, models are presented for molecular and Knudsen diffusion during flow through aggregates of solid particles at both atmospheric and low pressure permeametric conditions. For a randomly packed bed of granular particles, a cell model is developed that takes into account the tortuosity and variations in the cross-sectional area. A new analytical expression for the Kozeny constant is derived in terms of the bed porosity and particle shape. The effect of porosity on surface area measurements using permeability methods is explained.     

Effect of lipid excipients on in vitro pancreatic lipase activity

PURPOSE: To study the effects of two lipid excipients, Peceol and Gelucire 44/14 on the in vitro pancreatic lipase activity. METHODS: A 50 microL reaction mixture, consisting of 45 microL (3H) triolein as the radiolabeled substrate, 2.5 microL Peceol or Gelucire 44/14 (0.05-0.5%), either alone or in combination, 2.5 microL colipase (100 microg/mL), and 2.5 microL pancreatic lipase (1 mg/mL), was incubated for 10 min at room temperature. At the end of incubation, the reaction was stopped by the addition of an extraction solvent containing chloroform, methanol, and n-heptane (12.5:14:10), and the mixture vortexed briefly. Subsequently, 250 microL of 50 mM sodium carbonate was added and the aqueous and organic phase separated by centrifugation for 5 min at 1000 g. One hundred microliters of the supernatant was transferred to a scintillation counter and then radioactivity measured after the addition of 3.6 mL of scintillation fluid. Pancreatic lipase activity was determined by measuring the amount of free fatty acid released into the incubation medium and expressed as micromol free fatty acid released/min. RESULTS: When used alone, Peceol inhibited the pancreatic lipase activity significantly in a concentration-dependent manner, with a maximum inhibition of 57% at 0.4% of the excipient [p < 0.05, one-way analysis of variance (ANOVA)]. Similarly, Gelucire 44/14 alone caused inhibition of lipase activity in a concentration-dependent manner. However, the maximum inhibition (30%) was smaller in magnitude compared with the former agent. When the two excipients were used in combination, the inhibitory effects on the enzyme activity were similar to those observed with the individual agents (p < 0.05, one-way ANOVA). However, the maximum inhibition of 30% was lower than that observed with Peceol alone. CONCLUSIONS: The results from this study suggest that these lipid excipients inhibit in vitro pancreatic lipase activity and should be taken into consideration when developing oral formulations using these agents.     

Synthesis and characterization of precursor derived TiN@Si–Al–C–N ceramic nanocomposites for oxygen reduction reaction

The development of efficient and durable catalysts is critical for the commercialization of fuel cells, as the catalysts’ durability and reactivity dictate their ultimate lifetime and activity. In this work, amorphous silicon-based ceramics (Si–C–N and Si–Al–C–N) and TiN@Si–Al–C–N nanocomposites were developed using a precursor derived ceramics approach. In TiN@Si–Al–C–N nanocomposites, TiN nanocrystals (with sizes in the range of 5–12 nm) were effectively anchored on an amorphous Si–Al–C–N support. The nanocomposites were found to be mesoporous in nature and exhibited a surface area as high as 132 m²/g. The average pore size of the nanocomposites was found to increase with an increase in the pyrolysis temperature, and a subsequent graphitization of free carbon was observed as revealed from the Raman spectra. The ceramics were investigated for electrocatalytic activity toward the oxygen reduction reaction using the rotating disk electrode method. The TiN@Si–Al–C–N nanocomposites showed an onset potential of 0.7 V versus reversible hydrogen electrode for oxygen reduction, which seems to indicate a 4-electron pathway at the pyrolysis temperature of 1000°C in contrast to a 2-electron pathway exhibited by the nanocomposites pyrolyzed at 750°C via the Koutecky–Levich plot.     

Infrared Heating as a Disinfestation Method Against <Emphasis Type="Italic">Sitophilus oryzae</Emphasis> and Its Effect on Textural and Cooking Properties of Milled Rice

Infrared (IR) heating method against rice weevils (Sitophilus oryzae) in an egg stage was investigated. A kinetic model was developed to describe insect mortality in a temperature range of 40–60 °C. Effects of IR heating temperature (50–60 °C) and exposure time (1–3 min) on insect mortality and quality attributes of the treated rice were evaluated. The optimized condition obtained by means of the response surface method was used to analyze rice quality before and after IR treatment with storage. The results showed that the 0.5th-order thermal death kinetic equation was the most suitable model, and the S. oryzae eggs had less heat tolerance than the adults and some other species. Mortality achieved 100 % after 2 min for all temperatures. Both IR heating parameters significantly affected the treated milled rice qualities. The minimal changes in rice quality before and after storage could be obtained using optimized temperature and exposure time of 53.6 °C and 1.2 min, respectively.     

Differences in lipoprotein lipid concentration and composition modify the plasma distribution of cyclosporine

PURPOSE: The purpose of this study was to define the relationship between lipoprotein (LP) lipid concentration and composition and the distribution of cyclosporine (CSA) in human plasma. METHODS: 3H-CSA LP distribution was determined in normolipidemic human plasma that had been separated into different LP and lipoprotein-deficient plasma (LPDP) fractions by either affinity chromatography coupled with ultracentrifugation, density gradient ultracentrifugation or fast protein liquid chromatography. 3H-CSA LP distribution (at a concentration of 1000 ng/ml) was also determined in patient plasma samples with defined dyslipidemias. Furthermore, 3H-CSA LP distribution was determined in patient plasma samples of varying LP lipid concentrations. Following incubation, the plasma samples were separated into their LP and LPDP fractions by sequential phosphotungistic acid precipitation in the dyslipidemia studies and by density gradient ultracentrifugation in the specific lipid profile studies and assayed for CSA by radioactivity. Total plasma and lipoprotein cholesterol (TC), triglyceride (TG) and protein (TP) concentrations in each sample were determined by enzymatic assays. RESULTS: When the LP distribution of CSA was determined using three different LP separation techniques, the percent of CSA recovered in the LP-rich fraction was greater than 90% and the LP binding profiles were similar with most of the drug bound to plasma high-density (HDL) and low-density (LDL) lipoproteins. When 3H-CSA was incubated in dyslipidemic human plasma or specific patient plasma of varying LP lipid concentrations the following relationships were observed. As the very low-density (VLDL) and LDL cholesterol and triglyceride concentrations increased, the percent of CSA recovered within the VLDL and LDL fractions increased. The percent of CSA recovered within the HDL fraction significantly decreased as HDL triglyceride concentrations increased. The percent of CSA recovered in the LPDP fraction remained constant except in hypercholesterolemic/hypertriglyceridemic plasma where the percent of CSA recovered decreased. Furthermore, increases in VLDL and HDL TG/TC ratio resulted in a greater percentage of CSA recovered in VLDL but less in HDL. CONCLUSIONS: These findings suggest that changes in the total and plasma LP lipid concentration and composition influence the LP binding of CSA and may explain differences in the pharmacological activity and toxicity of CSA when administered to patients with different lipid profiles.