Bioactive polymers 66. Theophylline retardation in xanthan-based hydrogels

Xanthan has been reticulated with epichlorohydrin to obtain a hydrogel for use in drug retardation. The obtained gel shows swelling degrees up to 1000. Theophylline has been inserted by diffusion into this gel; concentrations around 150 mg theophylline/g dry hydrogel being obtained. Controlled release of theophylline has been established by elution in a close recirculation system. Zero-order kinetics has been obtained in the diffusion process of theophylline into the eluent, within a 14 h time interval.     

A comparative study of the pharmacokinetics and urinary metabolites of sustained-release theophylline syrup, granule and tablet preparations

Three different theophylline preparations, theophylline syrup, granule and tablets, were examined to determine their pharmacokinetics and changes in urinary metabolites for each steady state phase. The theophylline syrup was as rapidly and as essentially bioavailable as the theophylline granule preparation. In addition, peak to trough differences in serum theophylline concentrations were largest for theophylline syrup and lowest for tablets. Tmax was greater in theophylline tablets and a significant difference was apparent in the tablet-syrup and tablet-granule populations. AUC and T1/2 were similar in these populations. Cmax and Cmin achieved satisfactory therapeutic theophylline levels in three different preparations, and t-test showed no significant difference between them. CL and Vd were also similar. The urinary metabolites of theophylline were expressed as internal standard equivalents on a molar basis. There were no significant changes between either tested preparations different or different age groups. Therefore, we concluded that theophylline syrup and granules should be administered on a 3-times-daily basis, considering trough plasma theophylline levels. Theophylline tablets are preferable, if they can be taken.     

Drug transport mechanisms and release kinetics from molecularly designed poly(acrylic acid-g-ethylene glycol) hydrogels

Controlled drug release devices of pH-sensitive, complexing poly(acrylic acid-g-ethylene glycol) (P(AA-g-EG)) hydrogels were prepared by free radical solution UV polymerization. The effects of hydrogel composition, polymerization conditions and surrounding environment on theophylline release kinetics and drug transport mechanisms were evaluated in these P(AA-g-EG) polymer networks. Release studies indicated a dependence of the theophylline release kinetics and diffusion coefficients on the hydrogel structure, polymerization conditions and pH of the environment. The theophylline transport mechanism was studied by fitting experimental data to five different model equations and calculating the corresponding parameters. The Akaike information criterion was also considered to elucidate the best-fit equation. Results indicated that in most release cases, the drug release mechanism was anomalous (non-Fickian). This indicates that such systems may, under certain conditions, provide release characteristics approaching zero-order release. The pH of the dissolution medium appeared to have a strong effect on the drug transport mechanism. At more basic pH values, Case II transport was observed, indicating a drug release mechanism highly influenced by macromolecular chain relaxation. The results obtained in this research work lead us to the conclusion that P(AA-g-EG) hydrogels can be successfully used as drug delivery systems. Their versatility to be designed with specifically tuned release properties renders these biomaterials promising pharmaceutical carriers for therapeutic agents.     

Cellular volume determination of alginate-entrapped hepatocytes by MRI diffusion measurements

Cellular volume of hepatocytes entrapped in alginate gel beads were evaluated under in vivo conditions in samples having different cell densities by applying mathematical models to the diffusion data obtained by magnetic resonance imaging (MRI). The calculated average volume is in good agreement with the values from the literature-- being closer to the data relative to living tissue than to isolated cells. The non invasive characteristics of magnetic resonance imaging make this method particularly well suited to obtain information from the intact system.     

Fricke gel as a tool for dose distribution verification: optimization and characterization

With the introduction of conformal techniques in radiation therapy, gel dosimetry plays an important role as a 3D dose verification system. There are two main types of gels in use for dosimetry: Fricke gels and polymer gels. The advantages of polymer gels are improved dose response and stability with no diffusion problems. However, the more complicated fabrication procedure and the greater cost compared to Fricke gels makes polymer gels less attractive in routine clinical use. Dose resolution has recently been introduced as a concept for comparing and optimizing the performance of different types of gel dosimeters. This parameter has not yet been investigated for Fricke gels. In this study, the effect on the dose resolution and the diffusion from different gelatine- and Fe2+-concentrations and different pH was evaluated. Increasing the concentration of gelatine from 6 wt% to 10 wt% influenced the diffusion coefficient the most, while reducing the pH from 2.0 to 1.5 had the largest effect on the dose resolution. For a gel consisting of 10 wt% gelatine, 1.0 mM Fe2+ and pH 1.5 the diffusion coefficient was found to be 1.5 mm2 h-1 and the dose resolution was about 4.1% (at 95% confidence level), for a dose of 40 Gy. By evaluating different dose gradients by the gamma-method, the diffusion was shown to have no clinically relevant impact on the dose distribution and plan acceptance within 3 h of irradiation. The results indicate a potential use of Fricke gels for IMRT verification.     

Clinical laboratory application of HPLC

In clinical laboratory tests, high performance liquid chromatography (HPLC) has been widely used because of good reproducibility of data and easy automatization. In this workshop, separation of IgG and albumin in commercially available IgG preparation and determination of blood theophylline and serum uric acid levels were conducted by the HPLC method. In separation of IgG and albumin, HPLC analysis was carried out within 10 minutes by using the high-performance gel filtration column (TSK gel G 3,000 SWXL). Blood theophylline was fully automatically determined by using the pretreated column to separate small molecular material before application of the analytical column. A good correlation of blood theophylline levels between HPLC and ordinary EIA method was observed. In determination of serum uric acid, pretreatment for deproteinization of samples by acid was done to measure exactly the whole blood uric acid content. Eluent was adjusted to pH 2.2 to increase affinity to ODS phase of the reversed column (TSK gel ODS-80 TM). There was a good correlation of values of uric acid between HPLC and uricase-catalase method.     

Dissolution behaviour of hydrophilic matrix tablets containing two different polyethylene oxides (PEOs) for the controlled release of a water-soluble drug. Dimensionality study.

Hydrophilic matrix tablets containing polyethylene oxides as the retarding polymer have been successfully employed in the controlled release of drugs. To evaluate the relative influence of drug diffusion and polymer erosion mechanisms in the drug delivery process, we studied the hydration behaviour of matrix tablets containing a water-soluble drug and PEOs of two different molecular weights: Polyox WSRN 1105 (Mw = 0.9 x 10(6)) and Polyox WSRN 301 (Mw = 4 x 10(6)). The hydration rate, the extent of swelling, and the erosion rate of matrices containing the polymer, the drug and tableting excipients were evaluated in comparison to tablets made of pure polymer. The results of these studies on function of the release behaviour were then discussed. The results show that the higher molecular weight PEO swells to a greater extent and tends to form, upon hydration, a stronger gel, which is therefore less liable to erosion, if compared to the lower molecular weight PEO. This difference in the erosion behaviour can explain the different efficiencies of the two polymeric products in modulating the delivery rate of the water-soluble drug. Moreover, the presence of other soluble components (drug and excipients) in the dosage form enhances the erosion trend of the tablets with a consequent reduction of the efficiency of the polymer in drug release control.     

Reaction–diffusion modelling for microphysiometry on cellular specimens

Using modeling and simulation, we quantify the influence of spatiotemporal dynamics on the accuracy of data obtained from sensors placed in microscaled reaction volumes. The model refers to cellular reaction (i.e. proton extrusion and oxygen consumption) in complex, buffering solutions. Whole cells or viable tissues cultured in such devices are monitored in real time with integrated sensors for pH and dissolved oxygen. A 3D finite element model of diffusion and metabolic reaction was set up. With respect to pH, the effect of buffering species on proton diffusion is analysed in detail. To account for the delayed time response of real sensors, the sensor impulse response time was implemented by linear convolution. A validation of the model has been achieved by an electrochemical approach. The model reveals significant deviations of measured pH and O₂, and values of these parameters actually occurring at different sites of the cell culture volume. It is applicable to any setting of (bio-) sensors involving reaction and diffusion of dissolved gases and particularly H⁺ ions in buffered solutions.     

Diffusion blotting for rapid production of multiple identical imprints from sodium dodecyl sulfate polyacrylamide gel electrophoresis on a solid support

A simple and fast method for diffusion blotting of proteins from precast SDS-PAGE gels (0.5 mm) was developed. The efficiency of protein transfer was evaluated using labelled proteins. Diffusion blotting for three minutes, gave a transfer of 10% compared to electroblotting. By doubling the transfer time for each subsequent imprint, four imprints were made from the same lane with similar amounts of protein transferred onto each imprint. With a transfer time of three minutes each, it was possible to obtain at least ten imprints with all the proteins visible in all the imprints. There was no detectable loss in resolution as compared to electroblotting. The method also works well with an immuno-detecting system. The number of imprints which can be obtained, is dependent on the sensitivity of the detection system and the amount of protein applied. The greatest advantage of diffusion blotting compared to electroblotting is that several imprints can be made from each lane, and different antisera can be tested on identical imprints. The gel remains on its plastic support which prevents it from stretching and compression; this ensures identical imprints and facilitates more reliable molecular mass determination. If only a few imprints are made, sufficient protein remains within the gel for general protein staining. These advantages make diffusion blotting the method of choice when quantitative protein transfer is not required.     

Evaluation of the imaging properties of two generations of a CCD-based system for digital chest radiography

Two generations of a CCD-based detector system with lens-based optical coupling for digital chest radiography were evaluated in terms of presampling MTF, NPS, NEQ, DQE, linearity in response, and SNR over the detector area. Measurements were performed over a wide exposure range and at several different beam qualities. Neither the presampling MTF nor the DQE showed any general strong beam quality dependence, whereas the NPS and NEQ did when compared at specific entrance air kerma values. The exposure dependency for the DQE was found to be considerable, with the detectors showing low DQE at low exposures, and higher DQE at higher exposures. It was found that the second generation has been substantially improved compared to its predecessor regarding all the relevant parameters. The DQE(0) at an entrance air kerma of 5 microGy increased from 9% to 15%, mainly due to a better system gain (including optical coupling efficiency and matching of the energy of the emitted light photons to the sensitivity of the CCD camera). The first generation of detectors was found to have problems with bad peripheral resolution [MTF(muN/2) <0.1]. This problem was nonexistent for the second generation for which uniform resolution has been obtained [MTF(muN/2)=0.3]. A theoretical calculation of the DQE of two model systems similar to the ones evaluated was also performed, and the results were comparable to the experimentally determined data at high exposures. The model shows that both systems suffer from low optical coupling efficiency due to the large demagnification used. The main conclusion is that although the second generation has been improved, there is still a problem with low system gain leading to relatively modest DQE values, especially at low exposures.     

The relationship of cerebrospinal fluid and plasma theophylline concentrations in children and adolescents taking theophylline

Ten ambulatory subjects with asthma experienced a seizure while they were receiving oral theophylline preparations and were evaluated prospectively according to a set protocol. The protocol included a lumbar puncture that permitted the simultaneous determination of plasma and cerebrospinal fluid (CSF) theophylline concentrations. A constant relationship was observed between the plasma theophylline concentration and that of the CSF. It was found that the theophylline concentrations in these two biologic fluids could be characterized by the regression equation y = 0.41 X + 0.7 where y is the CSF theophylline concentration and X is the plasma theophylline concentration. Two infants with hydrocephalus treated by ventriculoperitoneal shunt were also simultaneously evaluated for plasma and CSF theophylline concentrations. These infants demonstrated greater than expected entry of theophylline into the CSF. Some central nervous system abnormalities may be characterized by increased theophylline entry into the CSF.     

A computational solution of mathematical model for oxygen transport in peripheral nerve

Time-dependent transport of oxygen in a peripheral nerve by simulating oxygen release, diffusion, chemical reactions and consumption in capillaries and surrounding peripheral nerve tissue using Krogh cylinder symmetry has been studied. Radial diffusion of oxygen is from a capillary to a surrounding cylinder tissue and axial diffusion to arterial distance to veins. A monoexponential or bioexponential function characterizes the approach of the oxygen tension to a new value. The time-dependent transport of oxygen in peripheral nerve with forward and backward reactions has been considered in this mathematical model which makes it different from earlier-studied models. A numerical technique has been used to find the solution.     

Bioavailability of Theophylline from Three Different Tablets in Asthmatic Patients and Their Bronchodilating Effects in Combination with Terbutaline Inhalation

The bioavailability of three different theophylline tablets (microcrystallinic theophylline, Theolair®, Nuelin®, 3M Riker), choline theophyllinate as a new film-coated tablet (Teovent®, Ferrosan, Sweden) and theophyllaminopropanol (Oxyphylline® Draco, Sweden) was investigated in eight adult asthmatics in a randomized, double-blind, cross-over study.
Effects on ventilatory capacity (FEV₁ and FVC), circulation (heart rate and blood pressure) and skeletal muscle tremor were followed. The theophylline concentration was determined by gas chromatography. Forty-five minutes after theophylline administration the plasma concentrations were almost the same for all four formulations. The bioavailability was also almost identical. The half-life for intravenous theophylline in these asthmatics was 7.4 ± 0.64. The three tablet formulations had equal effect on FEV₁ and the effect was sustained throughout the 6-h period.
Six hours after theophylline administration five terbutaline inhalations induced the same further increase in FEV₁. The results indicate that theophylline alone has only a moderate acute bronchodilating effect at recommended plasma concentrations but gives a good effect when combined with inhaled β₂-adrenostimulants.     

Fast and simplified mapping of mean axon diameter using temporal diffusion spectroscopy

Mapping axon diameter is of interest for the potential diagnosis and monitoring of various neuronal pathologies. Advanced diffusion‐weighted MRI methods have been developed to measure mean axon diameters non‐invasively, but suffer major drawbacks that prevent their direct translation into clinical practice, such as complex non‐linear data fitting and, more importantly, long scanning times that are usually not tolerable for most human subjects. In the current study, temporal diffusion spectroscopy using oscillating diffusion gradients was used to measure mean axon diameters with high sensitivity to small axons in the central nervous system. Axon diameters have been found to be correlated with a novel metric, DDR_⊥ (the rate of dispersion of the perpendicular diffusion coefficient with gradient frequency), which is a model‐free quantity that does not require complex data analyses and can be obtained from two diffusion coefficient measurements in clinically relevant times with conventional MRI machines. A comprehensive investigation including computer simulations and animal experiments ex vivo showed that measurements of DDR_⊥ agree closely with histological data. In humans in vivo, DDR_⊥ was also found to correlate well with reported mean axon diameters in human corpus callosum, and the total scan time was only about 8 min. In conclusion, DDR_⊥ may have potential to serve as a fast, simple and model‐free approach to map the mean axon diameter of white matter in clinics for assessing axon diameter changes. Copyright © 2016 John Wiley & Sons, Ltd.     

A crosslinked system from scleroglucan derivative: preparation and characterization

Matrices obtained by a crosslinking reaction between the polycarboxylated derivative of scleroglucan (sclerox) and 1,6-hexanedibromide have been prepared and characterized. Different ratios between the alkane dihalide and sclerox yielded products with different properties. Water uptake by the hydrogel with a low degree of crosslinking was remarkably affected by ionic strength. The determination of the crosslink density is led by simultaneously solving two Flory equilibrium equations referring to two different conditions characterized by the presence or the absence of a salt in the swelling agent. Moreover, the swelling kinetics was studied by means of a recently proposed model. Finally, the permeation of two model molecules (theophylline and polystyrene sulphonate-sodium salt) through the hydrogels was evaluated.     

Production of monoclonal antibodies specific to theophylline-treated lymphocytes

The T11 molecule is reported to play a key role in T lymphocytes activation. Moreover, theophylline is known to modify the functional properties of T lymphocytes probably inducing early changes in T11 molecule during T cell activation. Aim of our work was to clarify the effect on T lymphocyte surface after in vitro treatment with theophylline. In this paper, we describe the production and the functional properties of several monoclonal antibodies obtained by immunizing Balb/c mice with theophylline treated cells. Some of the monoclonal antibodies reacted only with the theophylline-treated lymphocytes and showed a promitogenic activity, enhancing the expression of T activated cell antigen. These monoclonal antibodies seem to demonstrate the existence of a membrane molecule which appears on lymphocytes surface after a trigger signal occurring in the early stages of T cell activation likely related to the T11 dependent alternative pathway.     

Theophylline and cAMP inhibit lysophosphatidic acid-induced hyperresponsiveness of bovine tracheal smooth muscle cells

We have established an in vitro model of airway hyperresponsiveness, using a bovine tracheal smooth muscle cell (BTSMC)-embedded collagen gel lattice. When the gel was pretreated with lysophosphatidic acid (LPA), which activates the small G protein RhoA, ATP- and high K⁺ solution-induced gel contraction was significantly augmented. This was not due to the modulation of Ca²⁺ mobilizing properties, since ATP- and high K⁺-induced Ca²⁺ transients were not significantly different between control and LPA-treated BTSMC. Y-27632, an inhibitor of Rho-kinase, suppressed the LPA-induced augmentation of gel contraction, whereas it did not inhibit the contraction of control gels. Theophylline (> 1 μ m ) reversed the LPA-induced augmentation of gel contraction, whereas it inhibited control gel contraction only with a very high concentration (100 μ m ). We confirmed that theophylline increased the intracellular concentration of cAMP ([cAMP]_i) in BTSMC. Elevation of [cAMP]_i with dibutyryl cAMP or forskolin also reversed the LPA-induced augmentation of gel contraction. Furthermore, theophylline, as well as dibutyryl cAMP and forskolin, suppressed the LPA-induced membrane translocation of RhoA, indicating that they prevented airway hyperresponsiveness by inhibiting RhoA. We conclude from these results that theophylline inhibits LPA-induced, RhoA/Rho-kinase-mediated hyperresponsiveness of tracheal smooth muscle cells due to the accumulation of cAMP.     

The effect of calcium on the macromolecular properties of heparan sulfate.

Heparan sulfate from human aorta has been subjected to a physico-chemical analysis in buffers of physiological ionic strength containing either sodium chloride or calcium chloride. A molecular weight of 50,000 was obtained both in sodium and calcium solutions by sedimentation equilibrium and from sedimentation and diffusion coefficients. The values obtained for So20,w in sodium and calcium chloride solutions were 2.28 X 10(-13) and 2.70 X 10(-13) sec, respectively, and the corresponding values for Dl20,w were 2.7 X 10(-7) and 3.1 X 10(-7) cm2/sec, respectively. Diffusion coefficients calculated from data obtained by gel chromatography were in excellent agreement with those determined by conventional techniques. The results indicated that the molecule contracts in the presence of calcium, presumably due to an increased binding of counter-ions with a concomitant decrease in charge density. Circular dichroism spectra above 200 nm, where the substituted amino group contributes to the absorption, gave no indication of a conformational change in the polysaccharide upon transformation from the sodium to the calcium salt. When the polysaccharide was dissolved in a salt solution, physiological both in ionic strength and in sodium to calcium ratio, it sedimented as the sodium salt. The sedimentation coefficient, the diffusion coefficient and the apparent molecular weight all displayed a concentration dependence. This dependence was much less in calcium chloride than in sodium chloride in determinations of molecular weight. Therefore there are advantages in performing molecular weight determinations of glycosaminoglycans in calcium solutions.     

Laboratory evaluation of an automated antimicrobial susceptibility system

A newly introduced automated method for antibiotic susceptibility testing, AUTOBAC 1, has been evaluated by comparison with the disk agar diffusion method (Bauer-Kirby). A total of 2,518 strains of gram-positive (540) and gram-negative (1,978) organisms isolated from clinical specimens was examined by both methods with eight or ten antibiotics, including Tobramycin. An overall agreement of 97.4% was obtained when results were compared by individual antibiotic. However, many discrepancies were observed when individual genera or species were analyzed. Of 2,518 strains examined, 651 (26%) showed discrepancies in response to one or more antibiotics. Strains, showing discrepancies were re-examined by the broth dilution susceptibility method. The results obtained favored the disk agar diffusion method. Reproducibility experiments revealed a greater inconsistency in the AUTOBAC 1 system than in the agar diffusion test. It is concluded that although a rapid automated system for antibiotic sensitivity testing is desirable, the conventional disk agar diffusion method is easier to perform, more reliable, and a less expensive procedure for antibiotic sensitivity determination.     

琥珀酸美托洛尔HPMC骨架片释放影响因素研究

以羟丙基甲基纤维素（HPMC）为骨架材料，乙基纤维素（EC）为阻滞剂，采用湿颗粒压片法制备琥珀酸美托洛尔亲水凝胶骨架片，考察HPMC用量、HPMC黏度、EC用量、制备方法、压片压力、释放介质及转速对琥珀酸美托洛尔（MS）骨架片体外释药的影响。结果表明，MS骨架片体外释药符合Higuchi方程，药物释放机制是骨架溶蚀和药物扩散的综合效应；HPMC用量与黏度、阻滞剂用量、制备方法、压片压力对释放速率均有显著性影响；释放介质的pH值及转速对释放速率无显著性影响。