Thermodynamics and kinetics of joint action of antiviral agent tilorone and DMSO on model lipid membranes

Individual and joint action of two water-soluble drugs, DMSO and tilorone, on model l-α-dipalmitoylphosphatidylcholine (DPPC) membranes were studied in equilibrium and kinetic regimes by differential scanning calorimetry (DSC). For equilibrium experiments, the drugs were introduced during preparation of the model membrane. In kinetic studies, one of the drugs was added to the DPPC membrane already containing the other drug, and the effects of drug-membrane interactions were monitored in real-time regime. It was found that tilorone and DMSO had opposite effects on the membrane melting temperature, which were non-additive under joint introduction of these drugs. Analysis of kinetics of DSC profiles under drugs introduction allowed us to discriminate two processes in drug-membrane interactions with different characteristic times, i.e., drug sorption onto the membrane (minutes) and drug diffusion through stacks of lipid bilayers (hours). It was established that 0.1?mol% DMSO effectively enhanced membrane penetration for tilorone with the rate of tilorone diffusion being dependent upon the scheme of drugs administration. A model was proposed describing how sorption of a dopant onto lipid membrane could affect the membrane permeability for other dopants. Conditions were determined for enhancement of membrane permeability, as it was observed for DPPC/DMSO/tilorone system.     

Kinetics and mechanism of methylene blue sorption onto palm kernel fibre

The kinetics and mechanism of the sorptive removal of methylene blue dye from aqueous solution using palm kernel fibre as adsorbent have been investigated. Batch kinetic experiments were performed and system variables investigated includes pH and initial dye concentration. The kinetic data were fitted to the pseudo-first, pseudo-second, intraparticle diffusion and mass transfer models. The pseudo-first order reaction kinetics fitted to the experimental data only in the first 5 min of sorption and then deviated, while the pseudo-second order kinetic model was found to fit the experimental data for the entire sorption period with high coefficient of determination. Equations were developed using the pseudo-second order model, which predicts the amounts of methylene blue at any contact time and initial concentration within the given range. This suggests that the sorption of methylene blue onto palm kernel fibre follows a chemical activation mechanism. A mathematical relationship was also drawn between the equilibrium sorption capacity and the change in pH (ΔH⁺) at the end of the kinetic experiments with varying initial dye concentration, supporting the fact that chemical reaction (ion exchange) occurred and is important in the rate determining step. Mass transfer was found to be favoured at high concentrations while intraparticle diffusion was favoured at low concentrations.     

Computational Modeling of Tumor Response to Drug Release from Vasculature-Bound Nanoparticles

Systemically injected nanoparticle (NPs) targeting tumor vasculature offer a venue for anti-angiogenic therapies as well as cancer detection and imaging. Clinical application has been limited, however, due to the challenge of elucidating the complex interplay of nanotechnology, drug, and tumor parameters. A critical factor representing the likelihood of endothelial adhesion is the NP vascular affinity, a function of vascular receptor expression and NP size and surface-bound ligand density. We propose a theoretical framework to simulate the tumor response to vasculature-bound drug-loaded NPs and examine the interplay between NP distribution and accumulation as a function of NP vascular affinity, size, and drug loading and release characteristics. The results show that uniform spatial distribution coupled with high vascular affinity is achievable for smaller NPs but not for larger sizes. Consequently, small (100 nm) NPs with high vascular affinity are predicted to be more effective than larger (1000 nm) NPs with similar affinity, even though small NPs have lower drug loading and local drug release compared to the larger NPs. Medium vascular affinity coupled with medium or larger sized NPs is also effective due to a more uniform distribution with higher drug loading and release. Low vascular affinity hampered treatment efficacy regardless of NP size, with larger NPs additionally impeded by heterogeneous distribution and drug release. The results further show that increased drug diffusivity mainly benefits heterogeneously distributed NPs, and would negatively affect efficacy otherwise due to increased wash-out. This model system enables evaluation of efficacy for vascular-targeted drug-loaded NPs as a function of critical NP, drug, and tumor parameters.     

Kinetic and thermodynamic analyses of adhesion of a peptide,Trp-Lys-Tyr-Met-Val-D-Met (WKYMVm), and human formyl peptide receptor (hFPR)

The kinetic and thermodynamic properties of a peptide–receptor interaction was investigated by measuring the adhesion force in the reaction via atomic force microscopy (AFM). Trp-Lys-Tyr-Met-Val-D-Met (WKYMVm), considered as a model system in the present study, is a potent neutrophil chemo-attractant. Since being identified as an agonist for formyl peptide receptor (FPR), WKYMVm’s high affinity to FPR has been verified through investigation of its kinetic and physiological behaviors via conventional methods. However, there have been no reports on the adhesion force of WKYMVm-FPR. In this research, we measured the adhesion force of WKYMVm-FPR using AFM. Kinetic parameters obtained from the relationship between the adhesion force and loading rate were used to characterize the thermodynamic properties of WKYMVm-hFPR binding.     

Sorptive removal of Methylene blue from aqueous solution using palm kernel fibre: Effect of fibre dose

The use of palm kernel fibre, a readily available agricultural waste product for the sorption of Methylene blue from aqueous solution and the possible mechanism of sorption has been investigated at various fibre doses. The extent of dye removal and the rate of sorption were analyzed using two kinetic rate models (pseudo-first and pseudo-second-order kinetic models) and two diffusion models (intraparticle and external mass transfer models).

Analysis of the kinetic data at different sorbent dose revealed that the pseudo-first order kinetics fitted to the kinetic data only in the first 5 min of sorption and then deviated from the experimental data. The pseudo-second-order kinetic model was found to better fit the experimental data with high correlation coefficients at the various fibre dose used. The dye sorption was confirmed to follow the pseudo-second-order model by investigating the relationship between the amount of dye sorbed and the change in hydrogen ion concentration of the dye solution and also the dependence of dye uptake with solution temperature. It was found that the change in hydrogen ion concentration and increase in sorption temperature were directly related to the amount of dye sorbed, and activation energy was calculated to be −39.57 kJ/mol, indicating that the dye uptake is chemisorption, involving valence forces through sharing or exchange of electrons between sorbent and sorbate as covalent forces.

The intraparticle diffusion plots showed three sections indicating that intraparticle diffusion is not solely rate controlling. The intraparticle diffusion and mass transfer rate constants where observed to be well correlated with sorbent dose in the first 5 min of sorption, indicating sorption process is complex. It was found that at low sorbent dose the mass transfer is the main rate controlling parameter. However at high sorbent dose, intraparticle diffusion becomes rate controlling.     

Controlled release from triple layer,donut-shaped tablets with enteric polymers

The purpose of this research was to evaluate triple layer, donut-shaped tablets (TLDSTs) for extended release dosage forms. TLDSTs were prepared by layering 3 powders sequentially after pressing them with a punch. The core tablet consisted of enteric polymers, mainly hydroxypropyl methylcellulose acetate succinate, and the bottom and top layers were made of a water-insoluble polymer, ethyl cellulose. Drug release kinetics were dependent on the pH of the dissolution medium and the drug properties, such as solubility, salt forms of weak acid and weak base drugs, and drug loading. At a 10% drug loading level, all drugs, regardless of their type or solubility, yielded the same release profiles within an acceptable level of experimental error. As drug loading increased from 10% to 30%, the drug release rate of neutral drugs increased for all except sulfathiazole, which retained the same kinetics as at 10% loading. HCl salts of weak base drugs had much slower release rates than did those of neutral drugs (eg, theophylline) as drug loading increased. The release of labetalol HCl retarded as drug loading increased from 10% to 30%. On the other hand, Na salts of weak acid drugs had much higher release rates than did those of neutral drugs (eg, theophylline). Drug release kinetics were governed by the ionization/erosion process with slight drug diffusion, observing no perfect straight line. A mathematical expression for drug release kinetics (erosion-controlled system) of TLDSTs is presented. In summary, a TLDST is a good design to obtain zero-order or nearly zero-order release kinetics for a wide range of drug solubilities.     

Studies on the energy release of rice mitochondria under different conditions by means of microcalorimetry

The thermodynamic and kinetic behaviors of energy release of mitochondria isolated from rice (Oryza sative L.) were studied by using a LKB 2277 Bioactivity Monitor under different conditions. The thermogenesis curves of energy release of the rice mitochondria (which had been kept at 0-3 degrees C for 15 h and 40 day before the determination) were determined respectively at 25 and 30 degrees C, and the difference in shape of the thermogenesis curves and thermodynamic and kinetic characteristics were compared. The thermodynamic and kinetic parameters of energy release of the mitochondria in the thermogenesis increasing stage have been calculated, and the experimental thermokinetic equations of the thermogenesis have been established. The results indicated that the lower the temperature, the slower the energy release of the rice mitochondria. Both the thermogenesis and the energy release rate of the rice mitochondria increased after the mitochondria was kept at lower temperature for 40 days. One can use the methods to characterize the ability of the rice mitochondria to release energy under different conditions.     

Water sorption studies of hybrid biofiber-reinforced natural rubber biocomposites

Hybrid biofibers (sisal and oil palm) were incorporated into natural rubber matrix. The water absorption characteristics of the composites were evaluated with reference to fiber loading. The influence of temperature on water sorption of the composites is also analyzed. Moisture uptake was found to be dependent on the properties of the biofibers. The mechanism of diffusion in the gum sample was found to be Fickian in nature, while in the loaded composites, it was non-Fickian. Sisal and oil palm fibers were subjected to different treatments such as mercerization and silanation. The effect of chemical modification on moisture uptake was also analyzed. Chemical modification was seen to decrease the water uptake in the composites. The thermodynamic parameters of the sorption process were also evaluated. Activation energy was found to be maximum for the gum sample.     

Biosorption of uranium by magnetically modified Rhodotorula glutinis

Adsorption of uranium from aqueous solution onto the magnetically modified yeast cell, Rhodotorula glutinis, was investigated in a batch system. Factors influencing sorption such as initial solution pH, biomass dosage, contact time, temperature, initial uranium concentration and other common cations were analyzed. Sorption isotherm, kinetic and thermodynamic studies of uranium on magnetically modified R. glutinis were also carried out. The temperature dependent equilibrium data agreed well with the Langmuir model. Kinetic data obtained at different temperatures were simulated using pseudo-first-order and pseudo-second-order kinetic models, the pseudo-second-order kinetic model was found to describe the data better with correlation coefficients near 1.0. The thermodynamic parameters, ΔH°, ΔS° and ΔG° were calculated from the sorption data gained at different temperatures. These thermodynamic parameters showed that the sorption process was endothermic and spontaneous. All results indicated that magnetically modified R. glutinis can be a potential sorbent for uranium wastewater treatment.     

Thermo-sensitive chitosan based semi-IPN hydrogels for high loading and sustained release of anionic drugs

Thermo-sensitive poly(N-isopropyl acrylamide-co-vinyl pyrrolidone)/chitosan [P(NIPAM-co-NVP)/CS] semi-IPN hydrogels with improved loading capacity and sustained release for anionic drugs NAP were prepared by free-radical polymerization. The LCST of hydrogels was adjusted to the vicinity of body temperature by introducing hydrophilic NVP. The presence of CS in semi-IPN networks improves the swelling behavior and provides a high affinity for anionic drug NAP due to the strong interactions between NAP molecules and CS chains. Release of NAP was suppressed at pH 2.2 and 5.0 and accelerated at pH 7.4 due to the deprotonation of amino groups in CS. Increasing temperature above LCST, hydrogels showed a continuous release of NAP without burst diffusion due to the shrinkage of PNIPAM restraining the drug release.     

Improved energy coupling of human P-glycoprotein by the glycine 185 to valine mutation

A glycine 185 to valine mutation of human P-glycoprotein (ABCB1, MDR1) has been previously isolated from high colchicine resistance cell lines. We have employed purified and reconstituted P-glycoproteins expressed in Saccharomyces cerevisiae [Figler et al. (2000) Arch. Biochem. Biophys. 376, 34-46] and devised a set of thermodynamic analyses to reveal the mechanism of improved resistance. Purified G185V enzyme shows altered basal ATPase activity but a strong stimulation of colchicine- and etoposide-dependent activities, suggesting a tight regulation of ATPase activity by these drugs. The mutant enzyme has a higher apparent K(m) for colchicine and a lower K(m) for etoposide than that of wild type. Kinetic constants for other transported drugs were not significantly modified by this mutation. Systematic thermodynamic analyses indicate that the G185V enzyme has modified thermodynamic properties of colchicine- and etoposide-dependent activities. To improve the rate of colchicine or etoposide transport, the G185V enzyme has lowered the Arrhenius activation energy of the transport rate-limiting step. The high transition state energies of wild-type P-glycoprotein, when transporting etoposide or colchicine, increase the probability of nonproductive degradation of the transition state without transport. G185V P-glycoprotein transports etoposide or colchicine in an energetically more efficient way with decreased enthalpic and entropic components of the activation energy. Our new data fully reconcile the apparently conflicting results of previous studies. EPR analysis of the spin-labeled G185C enzyme in a cysteine-less background and kinetic parameters of the G185C enzyme indicate that position 185 is surrounded by other residues and is volume sensitive. These results and atomic detail structural modeling suggest that residue 185 is a pivotal point in transmitting conformational changes between the catalytic sites and the colchicine drug binding domain. Replacement of this residue with a bulky valine alters this communication and results in more efficient transport of etoposide or colchicine.     

Esterified coir pith as an adsorbent for the removal of Co(II) from aqueous solution

Coir pith was chemically modified for the adsorption of cobalt(II) ions from aqueous solution. Chemical modification was done by esterification using succinic anhydride followed by activation with NaHCO(3) in order to improve the adsorption of Co(II). Adsorptive removal of Co(II) from aqueous solution onto modified coir pith was evaluated in batch studies under varying conditions of agitation time and metal ion concentration to assess the kinetic and equilibrium parameters. A pseudo-second-order kinetic model fitted well for the sorption of Co(II) onto modified coir pith. Sorption kinetics showed that the loading of Co(II) by this material was quite fast under ambient conditions. The Langmuir and Freundlich equilibrium isotherm models provided excellent fits for the adsorption data, with R(2) of 0.99 and 0.98, respectively. After esterification, the maximum Co(II) sorption loading Q(0); was greatly improved. It is evident that chemically modified adsorbent exhibits better Co(II) removal capability than raw adsorbent suggesting that surface modification of the adsorbent generates more adsorption sites on its solid surface for metal adsorption. A complete recovery of the adsorbed metal ions from the spent adsorbent was achieved by using 1.0N HCl.     

Alcoholysis catalyzed by Candida antarctica lipase B in a gas/solid system obeys a Ping Pong Bi Bi mechanism with competitive inhibition by the alcohol substrate and water.

The kinetics of alcoholysis of methyl propionate and n-propanol catalyzed by Candida antarctica lipase B supported onto silanized Chromosorb P was studied in a continuous solid/gas reactor. In this system the solid phase is composed of a packed enzymatic sample and is percolated by nitrogen as carrier gas, which simultaneously carries substrates to the enzyme while removing reaction products. In this reactor the thermodynamic activity of substrates and effectors can be perfectly adjusted allowing kinetic studies to be performed under different operating conditions. The kinetics obtained for alcoholysis were suggested to fit a Ping Pong Bi Bi mechanism with dead-end inhibition by the alcohol. The values of all apparent kinetic parameters were calculated and the apparent dissociation constant of enzyme for gaseous ester was found very low compared with the one obtained for liquid ester in organic medium, certainly due to the more efficient diffusion in the gaseous phase. The effect of water thermodynamic activity was also investigated. Water was found to act as a competitive inhibitor, with a higher inhibition constant than n-propanol. Thus alcoholysis of gaseous methyl propionate and n-propanol catalyzed by C. antarctica lipase B was found to obey the same kinetic mechanism as in other non-conventional media such as organic liquid media and supercritical carbon dioxide, but with much higher affinity for the substrates.     

Multifunctional polyelectrolyte multilayer films: combining mechanical resistance, biodegradability, and bioactivity

Cross-linked polyelectrolyte multilayer films (CL PEM) have an increased rigidity and are mechanically more resistant than native (e.g., uncrosslinked) films. However, they are still biodegradable, which make them interesting candidates for biomedical applications. In this study, CL PEM films have been explored for their multifunctional properties as (i) mechanically resistant, (ii) biodegradable, and (iii) bioactive films. Toward this end, we investigated drug loading into CL chitosan/hyaluronan (CHI/HA) and poly(L-lysine)/hyaluronan (PLL/HA) films by simple diffusion of the drugs. Sodium diclofenac and paclitaxel were chosen as model drugs and were successfully loaded into the films. The effect of varying the number of layers in the (CHI/HA) films as well as the cross-linker concentration on diclofenac loading were studied. Diclofenac was released from the film in about 10 h. Paclitaxel was also found to diffuse within CL films. Its activity was maintained after loading in the CL films, and cellular viability could be reduced by about 55% over 3 days. Such a simple approach may be applied to other types of cross-linked films and to other drugs. These results prove that it is possible to design multifunctional multilayer films that combine mechanical resistance, biodegradability, and bioactivity properties into a single PEM architecture.     

Specificity and Affinity Quantification of Flexible Recognition from Underlying Energy Landscape Topography

Flexibility in biomolecular recognition is essential and critical for many cellular activities. Flexible recognition often leads to moderate affinity but high specificity, in contradiction with the conventional wisdom that high affinity and high specificity are coupled. Furthermore, quantitative understanding of the role of flexibility in biomolecular recognition is still challenging. Here, we meet the challenge by quantifying the intrinsic biomolecular recognition energy landscapes with and without flexibility through the underlying density of states. We quantified the thermodynamic intrinsic specificity by the topography of the intrinsic binding energy landscape and the kinetic specificity by association rate. We found that the thermodynamic and kinetic specificity are strongly correlated. Furthermore, we found that flexibility decreases binding affinity on one hand, but increases binding specificity on the other hand, and the decreasing or increasing proportion of affinity and specificity are strongly correlated with the degree of flexibility. This shows more (less) flexibility leads to weaker (stronger) coupling between affinity and specificity. Our work provides a theoretical foundation and quantitative explanation of the previous qualitative studies on the relationship among flexibility, affinity and specificity. In addition, we found that the folding energy landscapes are more funneled with binding, indicating that binding helps folding during the recognition. Finally, we demonstrated that the whole binding-folding energy landscapes can be integrated by the rigid binding and isolated folding energy landscapes under weak flexibility. Our results provide a novel way to quantify the affinity and specificity in flexible biomolecular recognition.     

β-Cyclodextrin hydrogels as potential drug delivery systems

β-cyclodextrins (βCD) are cyclic oligosaccharides which have been widely employed for pharmaceutical applications. Discs of insoluble polymers were synthesized by crosslinking β-cyclodextrins with the reagent epichlorohydrin. In this work, the possibility of employing a polymer containing 60 ± 3% βCD for drug delivery of two antiinflammatory (naproxen and nabumetone) and two antifungal drugs (naftifine and terbinafine) has been investigated. The interaction of Naproxen with the polymers was evidenced by X-ray diffractometry, FTIR spectroscopy and differential thermal analysis. Drug release kinetics were carried out at physiological conditions of pH and temperature, and kinetic and diffusion constants were calculated by fitting 60% of the release profile according to the Korsmeyer-Peppas equation. Also, diffusion coefficients were calculated according to the simplified Higuchi model. The drug release followed a simple Fickian diffusion mechanism for all the model drugs. This study suggests that these hydrogel matrices are potentially suitable as sustained release systems.     

Transport characteristics of a novel local drug delivery system using nordihydroguaiaretic acid (NDGA)-polymerized collagen fibers

The use of nordihydroguaiaretic acid (NDGA)-polymerized collagen fibers as a novel local drug delivery system is introduced. The drug loading of these biocompatible fibers is illustrated with the anti-inflammatory agents dexamethasone and dexamethasone 21-phosphate. Capillary zone electrophoresis was used to measure the amount of drug released from the fibers into phosphate buffered saline with time. From these measurements and the use of a mathematical model, we were able to determine the diffusion coefficients for dexamethasone (D = 1.86 x 10(-14) m2/s) and dexamethasone 21-phosphate (D = 2.36 x 10(-13) m2/s) in the NDGA collagen fibers. These values have not been previously reported. These fibers can be used to load other agents as well. The diffusion coefficient of any agent loaded in these fibers can be determined using the techniques and mathematical method described. The rate of drug release from the fibers can be controlled using a PLGA coating. The overall importance of this paper is the potential broad application of this novel drug delivery system for the treatment of various human diseases.     

Evaluation of drug release profile from patches based on styrene-isoprene-styrene block copolymer: the effect of block structure and plasticizer

We prepared pressure-sensitive adhesive (PSA) patches based on styrene-isoprene-styrene (SIS) thermoplastic elastomer using hot-melt coating method. The liquid paraffine is added in the PSA matrices as a plasticizer to moderate the PSA properties. Three drugs, methyl salicylate, capsaicin, and diphenhydramine hydrochloride are selected as model drugs. The Fourier transform infrared spectroscopy, differential scanning calorimetry test, and wide-angle X-ray diffraction test indicate a good compatibility between drugs and matrices. Peppas equation is used to describe drug release profile. Different drug-matrix absorption, as indicative of drug-matrix interaction, accounts for the variation in release profiles of different drugs. Furthermore, atomic force microscopy and rheological studies of the PSA samples are performed to investigate the effect of SIS structure and plasticizer of PSA on drug release behaviors. For methyl salicylate and capsaicin, drug diffusion in the PSA matrices is the main factor controlled by the release kinetic constant k. The high [SI] diblock content and high plasticizer amount in matrix provide the PSA with a homogeneous and soften microstructure, resulting in a high diffusion rate. But for water-soluble drugs such as diphenhydramine hydrochloride, the release rate is governed by water penetration with the competition from diffusion mechanisms.     

The release dynamics of salicylic acid and tetracycline hydrochloride from the psyllium and polyacrylamide based hydrogels (II)

Psyllium, a medicinally active natural polysaccharide, has been modified with polyacrylamide to develop the hydrogels; those can act as the potential candidate for novel drug delivery systems. In the present studies, the release dynamics of model drugs (salicylic acid and tetracycline hydrochloride) from the drug-loaded hydrogels have been discussed, for the evaluation of the drug release mechanism and diffusion coefficients. It has been observed that diffusion exponent ‘n’ have 0.68 and 0.74 values and gel characteristic constant ‘k’ have 1.625 × 10⁻² and 1.272 × 10⁻² values, respectively, for the release of salicylic acid and tetracycline hydrochloride in distilled water from the drug loaded hydrogels. Therefore, drug release from the drug loaded hydrogels through Non-Fickian or Anomalous diffusion mechanism where the rate of drug diffusion and rate of polymer relaxation were comparable. The effect of pH on the release pattern of tetracycline has been studied by varying the pH of the release medium. However, in each release medium, the Initial diffusion coefficient was observed to be more than the late time diffusion coefficient.     

Kinetic studies of the native and mutated intracellular beta-glucosidases from Cellulomonas biazotea

The mutation, conferring streptomycin and deoxyglucose resistance on cells, had profound effect on the kinetic and thermodynamic parameters inferring thermostabilization of beta-glucosidase from mutant 51 SM(r) of Cellulomonas biazotea. Free energy of activation for substrate binding, enthalpy and entropy of activation for irreversible denaturation of mutant-derived enzyme were decreased compared with enzyme from wild organism suggesting that the mutation partly stabilized the enzyme and that mutation made it more reactive.