Physical aging of progesterone-loaded poly(D,L,-lactide-co-glycolide) microspheres

PURPOSE

To study the interactions between a polymeric matrix and a drug during storage at a temperature lower than the glass transition temperature of the polymers.

METHODS

Poly(lactide-co-glycolide) microspheres loaded with different progesterone ratios were stored at 4. 20 and 40 degrees C. DSC-scans were recorded at regular intervals, depending on the storage temperature.

RESULTS

The physical aging of the polymeric matrix, as monitored by the amplitude of the endotherm associated with the glass transition, is slowed down by crystalline progesterone. The development of the progesterone polymorphic depends on the interface/volume ratio of the crystals.

CONCLUSIONS

For polymeric drug delivery systems, the determination of all studies parameters must take into account an effect of dispersed drugs which are more sensitive as the storage temperature is lower than the glass transition temperature of the matrix.

Internal morphology of poly(D,L-lactide-co-glycolide) BCNU-loaded microspheres. Influence on drug stability

The solvent extraction/evaporation process has been used to form poly(D,L-lactide-co-glycolide) (PLAGA) BCNU-loaded microspheres designed for use as intracranial controlled-release implants. Their actual payload could reach 25% with a 20-50 microns size distribution. Scanning electron microscopy showed that such carriers had a smooth surface and a spherical geometry. Differential scanning calorimetry analyses carried out on drug-loaded microspheres established that the PLAGA Tg was markedly shifted towards the low temperatures along with the disappearance of the BCNU melting endotherm. Annealing experiments performed at room temperature did not induce any change of the loaded microsphere DSC profiles. These features indicated that the BCNU acted as a plasticizer for the coating material and formed with it a solid solution. Similarly, stability of encapsulated BCNU was assessed in different conditions of storage. It appeared that drug degradation increased with temperature increase: 5.4, 8.8, 32.4 and 51.2% of decomposition after 3 month storage at -18, 4, room temperature (RT) and 37 degrees C respectively. Since the free drug was stable at 4 degrees C and experienced only 10.6% decomposition at RT during the same storage time, the state of solid solution involving the intimate mixing of the drug and the polyester in the matrix favors a progressive decomposition of BCNU. However, keeping the microspheres 6 months at -18 degrees C or 3 months at 4 degrees C prevents a loss of drug superior to 10%.

Tensioactivity and supramolecular organization of the palmitoyl prodrug of timolol

PURPOSE

To improve the bioavailability of the ocular drug timolol by facilitating its transport through the cornea, an amphiphilic prodrug was synthesized via the addition of a palmitic chain by esterification. The present study was undertaken to investigate the physicochemical and tensioactive properties of the prodrug.

METHODS

The amphiphilic properties of the prodrug were firstly investigated by the Wilhelmy plate method. The textures generated by the supramolecular organizations of the ester were visualized by optical microscopy.

RESULTS

The prodrug clearly decreased the surface tension. Optical microscopy provided excellent evidence for the existence of lyotropic liquid crystalline phases: two isotropic but organized phases and a birefringent lamellar phase.

CONCLUSIONS

The results from the ensemble of studies undertaken to determine the amphiphilic properties of the prodrug were all in accord with its ability to form liquid crystalline phases. The liquid crystalline state of the prodrug is believed to introduce a delay in the drug pharmacological effect.

Surface characterization of poly(alpha-hydroxy acid) microspheres prepared by a solvent evaporation/extraction process

This work constitutes the first attempt to characterize the wettability of poly(alpha-hydroxy acid) (PAHA) microspheres in situ, prepared according to a complex process involving emulsification, solvent evaporation, washing and freeze-drying. The analysis of the flotation profile of the microspheres has allowed us to determine both advancing and receding contact angles at the microsphere/air/water interface and furnished information on the organization of poly(vinyl alcohol) (PVA) and bovine serum albumin (BSA) at the surface of the PAHA coating. By the comparison of contact angles measured from model surfaces obtained by sampling pure PAHA, PVA, BSA and mixed PVA/PAHA monolayers on glass and poly(methyl methacrylate) (PMMA) substrates, it was concluded that the emulsifier (PVA or BSA) was strongly anchored to the surfaces of the microspheres. The use of BSA to formulate the microspheres from a single oil-in-water emulsion led to dry particles having a hydrophobic surface. The unfolding of the hydrophilic segments of the BSA embedded at the surface of the microspheres, following immersion in water, increased the wettability of the microspheres by water. The same qualitative results were obtained when PVA was used to stabilize single emulsions. On the other hand, microspheres formulated from a double water-in-oil-in-water emulsion displayed no modifications of their wettability when immersed in water. This can be explained by the absence of mobility of the hydrophilic segments of the emulsifier which are blocked in the surface or at the subsurface of the polymer matrix.

Intestinal absorption of PLAGA microspheres in the rat

Rhodamine B-labelled poly (DL-lactide-co-glycolide) (PLAGA) microspheres of 2 different sizes, 1-5 microns and 5-10 microns, were administered as a single dose (1.44 x 10(9) and 1.83 x 10(8) particles, respectively) into the ileal lumen of adult rats. The content of rhodamine in the mesenteric vein and ileal lumen was analysed periodically from 10 min to 48 h as well as the distribution of microspheres in the intestinal mucosa and various other tissues. The concentration of rhodamine decreased progressively in the intestinal lumen and was negligible after 24 h. The number of microspheres in the mesenteric vein increased rapidly and reached a maximum after 4 h whatever the size of the particles. It then decreased progressively, but more rapidly with microspheres > 5 microns than with microspheres < 5 microns. The absorption efficiency was low for the former batch (about 0.11% of the administered dose) and higher for the latter (about 12.7%). The intraileal administration of free rhodamine B was followed by intense labelling of the epithelial cells and basement membranes in mesenteric lymph nodes, spleen, kidney and liver. PLAGA microspheres mainly crossed the intestinal mucosa at the site of Peyer's patches where microspheres of < 5 microns appeared after 3 h. Microspheres > 5 microns were retained in the ileal lumen. A few small microspheres were occasionally observed in the epithelial cells. Only the smallest particles were recovered in the liver, lymph nodes and spleen while basement membranes were always labelled. It is concluded that PLAGA microspheres could be useful for the oral delivery of antigens if their size is between 1 and 5 microns.

Effect of stereotactic implantation of biodegradable 5-fluorouracil-loaded microspheres in healthy and C6 glioma-bearing rats

OBJECTIVE

Poly(lactic acid-co-glycolic acid) (PLAGA) microspheres are promising systems for interstitial chemotherapy of brain tumors. They can be readily implanted by stereotaxy and are biocompatible with the brain, in which they are totally biodegraded within 2 months. 5-Fluorouracil (5-FU) was selected for encapsulation, because this hydrophilic and antimetabolic drug is not directly neurotoxic and does not readily cross the blood-brain barrier. Also, its anticancer activity may be improved by sustained administration. Furthermore, it is a potent radiosensitizer.

METHODS

To study their fate and toxicity, two types of 5-FU-loaded PLAGA microspheres were implanted in healthy rats by stereotaxy. One type presented a fast in vitro release profile (FR), and the second exhibited a slow in vitro release pattern (SR) (100% of the encapsulated 5-FU is released within 72 hours and 18 days, respectively). Periodically, rats were killed for microscopic examination. The efficacy of these microspheres on rat glioma was then evaluated. Seven days after stereotactic implantation of C6 malignant glioma cells in the brain, the rats were treated by intratumoral injection of 5-FU solution, blank microspheres, or 5-FU-loaded microspheres (FR and SR types). The mortality of these treated groups was compared by the log-rank test with that of an untreated group.

RESULTS

After implantation of two types of 5-FU-loaded PLAGA microspheres, no sign of clinical or histological toxicity was observed. Entrapped 5-FU crystals were observed until Days 12 and 20 postimplantation within FR and SR microspheres, respectively, which suggests a longer releasing period in vivo than in vitro. In the therapeutic evaluation, only intratumoral implantation of SR-type 5-FU-loaded microspheres significantly decreased the mortality (P = 0.017).

CONCLUSION

5-FU-loaded PLAGA microspheres were implanted in rat brains without evident toxicity. Histological examination suggested a longer sustained delivery period in vivo than in vitro. Intratumoral implantation of SR-type 5-FU-loaded microspheres decreased the mortality of C6 tumor-bearing rats. This effect can be related to the local and the sustained delivery of the drug, because 5-FU administered systemically is ineffective against brain tumors.

Formulation of BCNU-loaded microspheres: influence of drug stability and solubility on the design of the microencapsulation procedure

The design of a microencapsulation procedure for the preparation of biodegradable BCNU-loaded microspheres used as intracerebral implants is the aim of this work. This approach will give sustained high local concentrations of the anti-tumour drug in the brain without the associated significant systemic toxicity. The microencapsulation technique used is a solvent-evaporation process based on the formation of an oil-in-water emulsion. The stability of BCNU in methylene chloride saturated with water and its high value of partition coefficient between methylene chloride and water justifies the selection of this organic solvent as the dispersed phase in the methodology. A spectrophotometric method for the quantification of BCNU in mixtures containing PLAGA is developed which allows the evaluation of drug photodecomposition. The volume of methylene chloride and the concentration of PVA in the external aqueous phase are the two variables that induce the largest variations of the microsphere size. The two main process parameters leading to the highest microencapsulation yield are the polymer concentration in the organic phase and the volume of the external aqueous phase; whereas the pH of the external aqueous phase and the use of co-solvents in the organic phase lead only to a small improvement in microsphere payload.

Diffuse scattering in protein crystallography

The understanding of flexibility and deformability in proteins is one of the current major challenges of structural molecular biology. The knowledge of the average atomic positions of three-dimensional folding of proteins, which is obtained either by X-ray diffraction or n.m.r. spectroscopy, is generally not sufficient to explain their functional mechanisms. Very often it is necessary to consider the existence of other concerted atomic motions as, for example, in the well-known case of the CO molecule fixation at the active site of myoglobin which requires the concerted displacement of a large number of atoms in order to open a channel down to this site. This opening, which depends on the physico-chemical conditions, plays the role of a regulator in the biochemical reactions (Janin & Wodak, 1983; Tainer et al. 1984; Westhof et al. 1984; Ormos et al. 1988).

Preparation and characterization of 5-fluorouracil-loaded microparticles as biodegradable anticancer drug carriers

To provide a device releasing 5-fluorouracil in a controlled manner and injectable into the brain by stereotaxy, biodegradable poly ((+/-)-lactide-co-glycolide) (PLAGA) microparticles were prepared by an emulsion-extraction process. Although the solubility profile of the drug was not suitable for its encapsulation by the aforementioned method, careful choice of process variables allowed significant drug loading, reaching 30%. Thus, the size of the 5-fluorouracil crystals, the organic phase/aqueous phase ratio, the theoretical drug loading and the microparticle size played a predominant role. The microsphere size was adjusted to 20-40 microns by selecting the appropriate PLAGA and polyvinylalcohol concentrations, and the stirring rate of the initial emulsion. It was shown that the microparticle structure depended directly on the experimental conditions governing the precipitation rate of the coating material: two types of microparticles, I and II, were characterized. The morphology of the particles influenced the 5-fluorouracil-release patterns, as did other process parameters, such as the 5-fluorouracil crystal size and the PLAGA concentration. It was possible to sustain the 5-fluorouracil release over 18 days.

In vitro study of the anti-leishmanial activity of biodegradable nanoparticles

Leishmania are obligate intracellular parasites, responsible for leishmaniasis. Leishmaniasis are transmitted via insect vector to vertebrate hosts including humans. The infection was reproduced in vitro with promastigotes which can infect murine resident peritoneal cells. Amphotericin B was incorporated into poly(D, L-lactide-co-glycolide) nanoparticles, biodegradable drug carriers, to allow specific targeting inside the cell. The interaction of the drug with infected cells was determined by exposing macrophage cultures to drug carriers. The toxic effects of polymeric drug carriers were defined prior to exposing cells to drug-loaded nanoparticles. For contact times up to 4h, cells tolerated polymer concentrations of 0.01%. The viability of parasites after treatment was determined. Infected macrophages were incubated at 26 degrees C (which allows the transformation of amastigote to promastigote) along with loaded and unloaded nanoparticles, as well as the free drug alone, and a count of the parasites in the medium was recorded. Anti-leishmanial activity was observed with drug-free nanoparticles. This activity may arise through the release of hydrogen peroxide following the activation of macrophages. The incorporation of amphotericin B did not enhance this effect. Interestingly, trehalose, a cryoprotector of the freeze-dried nanoparticles, altered parasite growth and activated macrophages.

Fate and biocompatibility of three types of microspheres implanted into the brain

The implantation of polymer devices in the brain that release neuroactive drugs locally and in a controlled manner is gaining increasing interest. The fates and tissue reactions of poly(epsilon-caprolactone), ethylcellulose, and polystyrene microspheres, prepared by the solvent evaporation method, radiosterilized by gamma-irradiation, and stereotactically implanted in rat brain have been studied by routine staining and immunohistochemistry. During the first few days after implantation, a nonspecific astrocytic brain tissue reaction was observed along with a macrophagous-microglial cell reaction typically found following any damage in the central nervous system, except in the presence of certain foreign body giant cells. Nine months into the experiment, microspheres appeared to be engulfed by histiocytic cells. The microsphere cluster was surrounded by a sheath composed of collagen and astrocytic cells. No necrosis was observed, suggesting the absence of toxicity. In some animals, however, an hydrocephalus developed as a result of obstruction of the medial ventricle by some microspheres.

Drug targeting into the central nervous system by stereotactic implantation of biodegradable microspheres

Controlled drug release in the central nervous system through an implantable polymeric vector has been developed in recent years. For this purpose, different polymeric devices composed primarily of synthetic biocompatible and biodegradable polymers have been investigated. The first polymeric devices developed were macroscopic implants (monolithic devices), which required open surgery for implantation. Microencapsulation methods, however, allow the production of microparticles or nanoparticles loaded with neuroactive drugs. Because of their size, these micro- or nanoparticles may be easily implanted by stereotaxy in discrete, precise, and functional areas of the brain without causing damage to the surrounding tissue. Presently, this method is most frequently applied in the fields of neuro-oncology and neurodegenerative diseases, but neurologically, the potential applications of drug targeting by stereotactic implantation of drug-loaded particles are legion.

Correlated intramolecular motions and diffuse X-ray scattering in lysozyme

Correlated motions of protein atoms are of biological significance in processes involving ligand binding, conformational change and information transmission. X-ray scattering patterns from protein crystals contain diffuse scattering that originates from correlated displacements of atoms. Here we present experimental data on diffuse X-ray scattering from lysozyme crystals. We show that the diffuse scattering is similar in form to scattering derived from molecular dynamics simulation and normal mode analysis of the isolated protein, the normal modes giving the closest agreement with experiment.

Crystallization and preliminary X-ray investigation of barstar, the intracellular inhibitor of barnase

Crystals of barstar, the intracellular inhibitor of the extracellular ribonuclease produced by Bacillus amyloliquefaciens (barnase), were obtained through vapor phase equilibration using the hanging drop technique. Three crystal forms have been characterized. Forms I and II, crystallized either in potassium phosphate or sodium citrate, are tetragonal; they exhibit a superstructure along the c-axis. Form III crystals, suitable for a high resolution structure determination, were grown from 55-65% ammonium sulfate. This crystal form is hexagonal and diffracts to at least 2 A resolution at a synchrotron radiation source. It belongs to the hexagonal space group P6, with unit cell dimensions a = b = 143.6 A, c = 35.6 A. There are four molecules of barstar in the asymmetric unit. X-ray data have been collected to 2.2 A Bragg spacing. The structure determination is underway in order to analyze conformational changes of barstar upon complexation with barnase.

Biodegradation and brain tissue reaction to poly(D,L-lactide-co-glycolide) microspheres

The therapeutic application of neuroactive molecules in neuroscience is limited, due to the problems posed by the administration of these drugs (peripheral metabolism, systemic effect and passage of the blood-brain barrier). One solution is the implantation in the brain of biodegradable polymer devices with controlled release of a neuroactive drug. The biodegradation and tissue reaction of the copolymer poly(D,L-lactide-co-glycolide) microspheres prepared by the solvent evaporation method, radiosterilized and stereotactically implanted in the rat brain were studied by routine staining, immunohistochemistry and transmission electronic microscopy. The brain tissue reaction observed was a non-specific astrocytic proliferation and a macrophagous-microglial cell reaction, typically found following damage to the central nervous system. Some foreign-body giant cells were observed and the inflammatory and macrophagous reaction decreased dramatically after 1 month and almost ended after 2 months when the microspheres were totally biodegraded. The copolymer poly(D,L-lactide-co-glycolide) microspheres may be considered biocompatible to the brain tissue.

Preliminary evaluation of a series of amphiphilic timolol prodrugs: possible evidence for transscleral absorption

A series of amphiphilic esters of timolol malonate (octanoyl, decanoyl, dodecanoyl, myristoyl and palmitoyl timolol) were tested in rabbits for their capacity to antagonise the isoproterenol-induced ocular hypotension, using timolol maleate as reference standard. The most active prodrug, palmitoyl timolol malonate (PTM) was also evaluated for its capacity: (a) to decrease IOP in a model of bethamethasone-induced ocular hypertension, and (b) to permeate "in vitro" through rabbit corneal tissues. PTM, the prodrug with the longest aliphatic chain and therefore the greatest amphiphilic/lipophilic character, showed "in vivo" significant activity differences with respect to timolol maleate: the beta-antagonism was more important at earlier and later experimental times, and the IOP decrease was more marked at longer times. The prodrug, however, showed "in vitro" an inferior corneal permeability when compared with timolol maleate. The significant differences observed for the beta-antagonism of PTM at earlier times of the test might be attributed to transscleral absorption, due to the physicochemical characteristics of the prodrug, while the prolonged action (also observed in the IOP-depression test) might be due to sustained release, resulting from accumulation of the prodrug in the corneal epithelium. The present preliminary results are indicative of the potentiality of amphiphilic properties in a prodrug molecule.

Synthesis of the orally macrofilaricidal and stable glycerolipidic prodrug of melphalan, 1,3-dipalmitoyl-2-(4'(bis(2''-chloroethyl)amino)phenylalaninoyl)gl ycerol

A new strategy is presented to develop macrofilaricidal compounds orally administered and able to concentrate in the lymphatic system. A diglyceride derivative of melphalan, 1,3-dipalmitoyl-2-(4'(bis(2''-chloroethyl)amino)phenylalaninoyl)gl y cerol, was synthesized. The esterification of melphalan by 1,3-dipalmitin allowed chemical stabilization of the alkylating agent in aqueous dispersion. No degradation of this prodrug was observed after a 3-month storage of an aqueous dispersion at 4 degrees C. The filaricidal activity of the prodrug was compared with those of melphalan in vitro against adults, infective larvae and microfilariae of Molinema dessetae, and evaluated in vivo on Molinema dessetae infected Proechimy oris. In vitro, melphalan and the glycerolipidic prodrug were inactive against microfilariae but active at 1 mmol/l against infective larvae and adults. In vivo studies were performed with rodents subcutaneously inoculated with infective larvae from Aedes aegypti. The number of macrofilariae was significantly reduced following treatment with a single oral dose of the alkylating agent prodrug (0.082 mmol/kg).

Ibuprofen-loaded ethylcellulose microspheres: analysis of the matrix structure by thermal analysis

The determination of the drug dispersion state in microspheres prepared by the solvent evaporation method is essential to foresee the stability of the particles and the drug release behavior. The present work deals with ibuprofen-loaded ethylcellulose microspheres, that are characterized by a lower drug melting point than the polymer glass transition temperature. Although annealing experiments were not possible, the study has evidenced the presence of a metastable molecular dispersion for intermediate loadings, coexisting with a solid solution and a crystalline dispersion of the drug in the polymer matrix. In addition, differential scanning calorimetry helped to distinguish between surface and inner ibuprofen crystals, which interact differently with the polymer matrix and therefore have different melting points.

A physicochemical study of the morphology of progesterone-loaded microspheres fabricated from poly(D,L-lactide-co-glycolide)

Progesterone-loaded microspheres are fabricated by a solvent evaporation process from a poly(D,L-lactide-co-glycolide) (85/15 PLG) and from alpha-progesterone. Methylene chloride is used as solvent and polyvinyl alcohol and methylcellulose are used as surfactants. The microspheres are characterized by scanning electron microscopy, differential scanning calorimetry, and x-ray powder diagrams. Our study shows that the morphology and the thermal behavior of PLG microspheres can vary significantly with progesterone loading and sample thermal history. Below and at 16.5% loading the microspheres exhibit a smooth outer surface. Above 23% loading, the surface becomes rough, embedded by copolymer particles or well-defined crystals. Pores and cracks can also be observed. Below 35% the progesterone is molecularly dispersed. At 35% and above crystal domains of the steroid appear and two crystalline forms are found: alpha- and beta-progesterone. The physical state of progesterone and the nature of its crystal domains dispersed in the PLG matrix can change during storage. Also a progressive development of an endothermic peak at the Tg event of the copolymer is observed during storage. No well defined relationship of peak size to progesterone loading can be shown.

Ibuprofen-loaded ethylcellulose microspheres: release studies and analysis of the matrix structure through the Higuchi model

The following work deals with ibuprofen-loaded ethylcellulose microspheres. The drug exists either in a state of molecular dispersion or in crystalline form, depending on the encapsulation ratio. The in vitro release profiles have been studied and the Higuchi model applied to the experimental results. With an appropriate treatment of the results, it has been shown that the surface crystals responsible for the observed burst effect are really encapsulated by the polymer. The calculation of the tortuosity factor clearly shows that the release kinetics are controlled by the hydrophobicity of ethylcellulose and the geometry of the porous volume resulting from the dissolution of ibuprofen crystals. It thus appears that crystals are probably differently distributed in the matrix depending on the microsphere size.

In vitro and in vivo degradation of poly(D,L lactide/glycolide) type microspheres made by solvent evaporation method

Microspheres of different poly(alpha-hydroxy acids) were prepared by solvent evaporation to study the effects of gamma-sterilization on stability and to establish the degradation process in vitro and in vivo. gamma-Irradiation dramatically decreases polymer molecular weight and this degradation continues on storage. gamma-Irradiation modifies the controlled release pattern of cisplatin-loaded microspheres. After embolization of rat livers by microspheres, a histological study of the inflammatory response was made, along with gel permeation chromatography analysis of degrading polymers. The degradation rate of the polymers increased with the glycolic unit content in the lactic chains. Scanning electron microscopy of microsphere degradation in vitro correlated with the former observations.

The highly concentrated liquid-crystalline phase of DNA is columnar hexagonal

The DNA molecule is extremely compacted in bacteria, in cell nuclei, sperm heads and virus capsids. These interactions between DNA molecules are important to our understanding of chromatin condensation. DNA forms multiple liquid-crystalline phases whose nature depends on the polymer concentration, and it has been suggested that the highly concentrated phase of 50-nm DNA molecules is two-dimensionally ordered and smectic-like. We rule out this smectic hypothesis and demonstrate by polarizing microscopy, electron microscopy and X-ray diffraction that this phase is characterized by a columnar longitudinal order and a hexagonal lateral order, with intermolecular distances ranging from 2.8 to 4.0 nm depending on the DNA concentration.

In-vitro evaluation of filaricidal activity of GABA and 1,3-dipalmitoyl-2-(4-aminobutyryl)glycerol HCl: a diglyceride prodrug

A diglyceride ester of gamma-aminobutyric acid (GABA) has been synthesized and its filaricidal activity compared with GABA, and progabide in-vitro, on infective larvae and microfilariae of Molinema dessetae, a rodent filaria. GABA induced paralysis in infective larvae but was inactive on microfilariae. There were interactions between the culture medium and GABA. The ester drug at 0.1 mmol L-1 (1,3-dipalmitoyl-2-(4-aminobutyryl)glycerol HCl) was as active as progabide on infective larvae and hundredfold more potent than GABA. Its microfilaricidal activity at 1 mmol L-1 was lower than that progabide at 0.1 mmol L-1 but a delayed effect was observed. The data confirm filariae sensitivity to GABA derivatives.

Coexistence of A- and B-form DNA in a single crystal lattice

It is well known that DNA can exist in a variety of conformations which can be interconverted by relatively mild changes in conditions. The in vivo conformation of DNA is usually thought to be the B form, but there is recent evidence that other conformations may be important in DNA-protein recognition. Different fragments of DNA crystallized under virtually identical conditions can form A, B or Z helices. A fragment that adopted an A conformation in a crystal was found in the B conformation in solution, whereas NMR spectroscopy of A-DNA films revealed the presence of a substantial amount of disordered B-DNA. Until now, however, a DNA fragment of a given sequence has not been crystallized in more than one global conformation. We report here an X-ray diffraction study of crystals of the DNA octamer dGGBrUABrUACC. In addition to a 'framework' of A-DNA, which gives discrete X-ray reflections, there are partially disordered B-DNA helices, recognized by their diffuse scattering features.

Doxorubicin-loaded nanoparticles: increased efficiency in murine hepatic metastases

Free doxorubicin and doxorubicin associated with polyisohexlycyanoacrylate were tested for their therapeutic efficiency in hepatic metastasis-bearing mice. The metastases originated from the M 5076 reticulum cell sarcoma. Irrespective of the dose and the administration schedule, the reduction of the number of metastases was much larger with the doxorubicin-loaded nanoparticles than with free doxorubicin. This was clearly confirmed by histological examination. Although pharmacological and pharmacokinetic data indicated a strong capture of the nanoparticles by the hepatic issue, the mechanism of nanoparticle therapeutic efficiency remains unclear.

Ion-exchange albumin microcapsules of doxorubicin: an in vitro release kinetic evaluation

Cross-linked albumin microcapsules were prepared, using a polycondensation interfacial process. Doxorubicin was incorporated in these microcapsules by simple adsorption from aqueous solution. Increasing the extent of cross-linkage of the microcapsule walls by either increasing the cross-linking agent concentration or the time of reaction significantly reduced the absorption ability of these microcapsules. Doxorubicin release kinetic evaluation revealed that the presence of a salt in the release medium was needed to enable much of the drug to be released. Furthermore, the doxorubicin displacement intensity from the microcapsules was dependent on the nature and concentration of the cations used, indicating that an ion-exchange process was involved. Analysis of the various doxorubicin release profiles, using ion-exchange kinetic equation, showed that the release kinetic process is governed by a film diffusion process at low and moderate Na+ ion concentrations in the exchanging solution, and by a particle diffusion process at high Na+ ion concentrations, sufficient to drive the doxorubicin exchange to completion.

Magnetically responsive microspheres for the pulsed delivery of insulin

This paper describes a new formulation for triggered delivery of insulin which consisted of magnetic particles dispersed in alginate spheres. When magnetic field was applied to that system, the release rate of insulin was about 50 times higher than in the absence of magnetic field. The influence of oscillating magnetic field was tested, in the same experimental conditions, on polyethylenimine cross-linked alginate spheres. In that case, the pulsed delivery of insulin occurred not immediately but during the period just after applying the magnetic field. The proposed magnetically responsive alginate spheres open new perspectives for the rhythmically delivery of peptides.

Binding mechanism of doxorubicin in ion-exchange albumin microcapsules

The absorption efficiency of cross-linked albumin microcapsules was evaluated as a function of various experimental conditions in an attempt to elucidate the doxorubicin binding mechanism of these microcapsules. The amount of drug absorbed augmented with increasing doxorubicin concentration until saturation was reached. Neither a Langmuir nor a Freundlich isotherm relationship was observed, indicating that the fixation of doxorubicin on the microcapsule walls did not follow a common physical adsorption process. Decreasing the mean particle diameter of the microcapsules increased the absorption rate and the total amount of doxorubicin absorbed, as expected. The absorption rate was enhanced by the elevation of the stirring rate of the aqueous drug solution. Furthermore, the presence of electrolytes in this aqueous solution profoundly altered the absorption profile of doxorubicin. Increasing the NaCl concentration in the solution reduced the total amount of drug absorbed. Moreover, the nature of the cation used also affected the absorption profile. These results suggested that there is a competitive fixation of the cation on the binding sites (identified as R-COO groups) available to the drug molecules. The weakly cross-linked microcapsules acted as cation-exchange resins which can exchange their labile sodium with the protonated drug present in the solution. This was also confirmed by the results of the titrimetric assay of the acidic microcapsules with NaOH.

Calcium and thiocyanate interactions with crosslinked albumin microcapsules: influence of the reticulation rate

Ca2+ and SCN- interactions with strongly or lightly crosslinked albumin microcapsules were studied, using 45Ca2+ for a pH range varying from 5.5 to 7.8 and 14SCN- ions for the range 2.15 to 3.0. With strongly crosslinked albumin, the Scatchard plots of equilibrium isotherms indicate a maximum number of binding sites for Ca2+ ions, when N is equal to 12 and an apparent association constant, K' is equal to 7.8 X 10(3) l/mol. For the weakly crosslinked albumin, this constant is equal to 11 X 10(3) l/mol and the variation of calcium absorption with pH has an unusual shape, with a maximum at pH 6.5. The measurement of SCN- ion absorption by lightly crosslinked microcapsules indicates a K' value of 5.4 X 10(3) l/mol and an N value of 7 for pH 2.15. These values are, respectively, 8.3 X 10(3) l/mol and 2 for pH 2.15 when using strongly crosslinked microcapsules.

Molecular dynamics studied by analysis of the X-ray diffuse scattering from lysozyme crystals

It is now well established that the biological activity of proteins is related not only to their mean molecular structure, but also to their intramolecular mobility. Nearly all techniques sensitive to dynamics have given evidence for intramolecular mobility in proteins: NMR, ESR, Raman spectroscopy, fluorescence quenching, Mössbauer spectroscopy, neutron scattering, measurements of elastic constants and hydrogen-deuterium exchange. The dynamics of proteins has also been approached by theoretical calculations. We report here investigations of the atomic and molecular displacements in hen egg-white lysozyme crystals using a new technique. This technique, based on the X-ray diffuse scattering analysis (scattering out of the Bragg reflections), can yield information on the atomic displacements, provided that they are correlated. Rigid-body molecular displacements, correlated along short rows of aligned molecules in two perpendicular directions, have been detected and analysed (mean square amplitude of the order of 5 X 10(-4) nm2). This technique can be also applied to the detection and analysis of intramolecular displacements.

5-Fluorouracil:carnauba wax microspheres for chemoembolization: an in vitro evaluation

5-Fluorouracil:carnauba wax microspheres were prepared using a meltable dispersion process with the aid of a surfactant as a wetting agent. It was noted that only hydrophilic surfactants were able to wet the 5-fluorouracil and substantially increased its content in the microspheres. No marked effect was observed in the particle size distribution of the solid microspheres as a function of the nature of the surfactant. Increasing the stirring rate in the preparation process decreased, first, the mean droplet size of the emulsified melted dispersion in the vehicle during the heating process, and, consequently, the mean particle size of the solidified microspheres during the cooling process. 5-Fluorouracil cumulative release from the microspheres followed first-order kinetics, as shown by nonlinear regression analysis. Although the kinetic results were not indicative of the true release mechanism from a single microsphere, it was believed that 5-fluorouracil release from the microspheres was probably governed by a dissolution process, rather than by a leaching process through the carnauba wax microspheres.

The formation and characterization of hydrocortisone-loaded poly((+/-)-lactide) microspheres

The solvent evaporation process has been used to form hydrocortisone-loaded microspheres from poly((+/-)-lactide) (PLA) and a lactide-glycolide copolymer (65/35). Methylene chloride was the casting solvent. Partially hydrolysed (88%) poly(vinyl alcohol) and methylcellulose were used as aqueous phase emulsifiers. Methylcellulose was preferred, because it gave stable emulsions as the amount of hydrocortisone being encapsulated increased whereas poly(vinyl alcohol) did not. With methylcellulose as the emulsifier, a broad size range of spherical microspheres containing up to 50% (w/w) hydrocortisone could be prepared. Thermal and X-ray analyses established that poly((+/-)-lactide) microspheres containing hydrocortisone retained thermal events characteristic of both materials. This is evidence that such microspheres contain, to some extent, crystalline hydrocortisone domains dispersed in a PLA matrix. But most of the encapsulated drug was molecularly dispersed in the PLA glass. The stability of hydrocortisone in microspheres was evaluated in different storage conditions: no degradation of drug was found. The release of hydrocortisone from 250-350 microns diameter microspheres into agitated 37 degrees C water (nitrogen atmosphere) was determined by HPLC analysis. The microspheres evaluated had initial hydrocortisone payloads of 12 to 47% (w/w). The rate of drug release increased as the initial drug payload carried by the microspheres increased. The release data are not adequately described by zero order, first order, or square-root-of-time release kinetics. Drug release from microspheres that contain 12% (w/w) hydrocortisone approached a plateau value well below the amount of drug actually carried by the microspheres. This is particularly true for hydrocortisone encapsulated in lactide-glycolide polymer.

Characterization of drug-loaded poly(d,l-lactide) microspheres

Lomustine and progesterone have been incorporated in biodegradable poly(d,l-lactide) microspheres by evaporating dichloromethane from stirred dichloromethane-in-water emulsions. Spherical microspheres with lomustine or progesterone payloads less than or equal to 23% were obtained. Higher lomustine payloads gave irregularly shaped particles. Microspheres with less than or equal to 68% progesterone were obtained, but free drug crystals formed on the surface of such microspheres. Increased agitation rates decreased mean microsphere size. Addition of drug to the dichloromethane phase increased average particle size relative to that obtained with drug-free microspheres prepared under the same experimental conditions. Complete evaporation of the dichloromethane, while the medium was continuously stirred, promoted formation of free drug crystals in the aqueous phase. Increased emulsifier concentrations did not significantly enhance drug incorporation efficiency within the microspheres. Shelf-life stability of lomustine and progesterone was reduced by incorporation in the microspheres, presumably due to their molecular dispersion in the poly(d,l-lactide).

[Trouble of liver function in polymyalgia rheumatica (author's transl)]

The possible existence of liver function disease such as cholestasis during temporal arteritis or polymyalgia rheumatica has been recently discovered. Two cases are reported of cholestasis without jaundice during polymyalgia rheumatica. The altérations most frequently observed are the elevation of the alcalin phosphatases, 5' nucleotidases, gamma G.T. and the retention of BSP. The syndrome disappears by treatment as well as the rheumatologic disease. It seems to be interesting to diagnose polymyalgia rheumatica through this trouble of liver funcion.

[Inversion of the right hemi-diaphragm associated with abundant pleural effusion (author's transl)]

The radiological appearance and the physiopathological consequences of the phenomenon of the inversion of the diaphragm on the left side associated with abundant pleural effusion, were studied by Felson and his school as early as 1965. Echotomography reveals that the phenomenon occurs on the right side in exactly the same way.