Drug retention and stability of solid lipid nanoparticles containing azidothymidine palmitate after autoclaving, storage and lyophilization.

Solid lipid nanoparticles (SLNs) were prepared using trilaurine (TL) as the SLN core and phospholipid (PL) as coating. Neutral and negatively charged PLs were used to produce neutral and negatively charged SLNs. An ester prodrug of 3'-azido-3'-deoxythymidine (Zidovudine, AZT), AZT palmitate (AZT-P), was synthesized and incorporated in the SLNs. The stability of SLN formulations containing AZT-P was studied at different temperatures. Drug retention and mean particle diameter of SLNs were determined after autoclaving, during temperature stability testing, and after lyophilization (with or without cryoprotective sugars) and reconstitution. There were no significant changes in the mean diameter and the zeta potential (zeta) of SLNs after autoclaving (121 degrees C for 20 min). The amount of incorporated AZT-P was, however, slightly reduced due to the formation of hydrosoluble AZT. Autoclaved SLNs were stable for a period of 10 weeks at 20 degrees C but an increase in particle size and loss of AZT-P were observed at 4 and 37 degrees C. Trehalose was an effective cryoprotectant for preventing SLN aggregation during lyophilization and subsequent reconstitution. Thermal gravimetric analysis showed that lyophilized preparations contained approximately 1% water. Using appropriate trehalose to lipid ratios, AZT-P retention in the SLNs was 100% after reconstitution. Our results demonstrate that SLNs containing AZT-P can be autoclaved, lyophilized and reconstituted without significant changes in SLN diameter and zeta potential or in the quantity of incorporated prodrug.

Evidence for phospholipid bilayer formation in solid lipid nanoparticles formulated with phospholipid and triglyceride.

PURPOSE: Solid lipid nanoparticles (SLN) are comprised of a high-melting point triglyceride (TG) core with a phospholipid (PL) coating. This study has investigated the possible formation of multiple PL bilayers on the TG core of SLN's as a function of increasing the PL:TG molar ratio. METHODS: Trilaurin (TL) was used as the SLN core. Dipalmitoylphos-phatdylcholine (DPPC) or a mixture of DPPC and dimyristoylphosphatidylglycerol (DMPG) were used to produce neutral and negatively charged SLN's. The volume of aqueous phase associated with the PL was determined using calcein and 6-carboxyfluorescein (6-CF) as hydrophilic markers incorporated during the preparation of the SLN's. RESULTS: The diameter of the SLN's decreased as the molar ratio of PL to TL was increased, until a PL:TL ratio of 0.15 was reached. After this point the diameter was not affected by further increases in the molar ratio. The experimental amount of PL required to prepare SLN's was significantly higher than the theoretical amount required to form a single monolayer on the surface. The aqueous volume associated with the PL was increased with increasing PL:TL molar ratios. CONCLUSIONS: The results obtained suggest that the formation of multiple PL bilayers is probable in SLN's prepared with a high molar ratio of PL to TL. The volume of the aqueous phase between the PL-bilayers, estimated from the amount of the hydrosoluble markers trapped in this phase, provides an indication of the relative number of bilayers at different PL:TL ratios.

Use of fractal dimension in the study of fractured surfaces of insulin zinc crystals.

The micromorphology of two types of insulin zinc crystals was characterized by computerized image analysis. It was demonstrated that one can identify the recombinant DNA crystals from those of animal origin in a blinded sample by perimeter fractal dimension analysis. Fractal dimension analysis was also applied in the study of irregularly fractured surfaces produced by thermal and mechanical stress. The results obtained suggest that the fractal dimension is related to the intensity of applied stress. The characterization of newly formed boundaries of insulin zinc crystals produced by mechanical or thermal stress could determine various surface-related kinetic processes.

Evaluation of the surface roughness of cystine stones using a visible laser diode scattering approach.

To understand the processes of fragmentation and the chemical reactivity of solids, proper characterization of surface topography is crucial. This paper describes a non-destructive technique of quantifying the surface roughness of cystine renal stones, using visible laser diode scattering and fractal geometry. Fragments of cystine stones were mounted on microscope slides and coated by a carbon-sputtering apparatus. The slides were placed under a dynamic active-vision system, using a visible laser diode to measure three-dimensional surface coordinates. The data obtained were analyzed by fractal geometry. Surface fractal dimensions were determined by the variation method. The results showed that the surface of a compact-size sample can be evaluated quantitatively. The technique is valuable for the accurate presentation of surfaces in three dimensions.

Reduced kallikrein excretion by liposome-encapsulated cyclosporin in the rat.

Different phospholipids and methods of preparation were used to produce cyclosporin encapsulated in liposomes. The optimal formulation of cyclosporin-liposome was compared to the oily cyclosporin after intraperitoneal administration of 25 mg kg-1 body weight to rats. Urinary kallikrein excretion was significantly reduced with the liposomal form. The abrupt increase of kallikrein excretion after the tenth day with the control oil preparation suggests that cyclosporin toxicity could be present at the tubular level, and the encapsulation of cyclosporin in liposomes reduces tubular damage.

Calcium oxalate crystal growth in the presence of mucin.

Using interfacially-controlled crystallization and gel diffusion crystallization methods, calcium oxalate monohydrate (COM), dihydrate (COD) and trihydrate (COT) crystals were grown by the slow diffusion of reacting ions in the presence of mucin. It was demonstrated that mucin in the growth media dramatically affected the size, habit, surface structure, thermodynamic stability and phase transition kinetics of hydrated calcium oxalate crystals. The results obtained revealed that mucin as a glycoprotein model controlled the growth of COT and COD single crystals as well as cluster formation. Growth inhibition of specific crystal faces and phase transition retardation occurred in its presence. The data confirmed that glycoproteins are more than just adhesive materials, enhancing crystal aggregation in stone formation.

The study of the surface geometry of renal stone fragments after shock wave and ultrasound disintegration.

Computerized image analysis was used for characterizing the irregular boundaries of calcium oxalate stone fragments resulting from shock wave and ultrasound disintegration. The complexity of the contour of the fragments was determined to evaluate the surface roughness of the rugged profile of the samples. Crack propagation on the crystal surface of the mineral phase was studied using fractal geometry. A significant difference was observed in the boundary variation of the calcium oxalate stone fragments treated by shock wave and ultrasound. Crack propagation in the mineral phase crystal was found to depend on the method of fragmentation used. There is also an experimental evidence that the surface topography of the stone fragments produced by shock wave depends on the microhardness of the stone material.

Effect of surface geometry and morphic features on the flow characteristics of microsphere suspensions.

In this paper we present a study on the effect of surface ruggedness of microspheres on the rheological behavior of their suspensions. For this purpose, different types of ragweed pollen grains were selected as models of natural microspheres. A computer-image processing system based on Fourier and fractal analysis of the contour was used to quantitate the micromorphology and surface roughness. The viscosity of suspensions, prepared by the dispersion of the different types of microspheres in heavy liquid paraffin, was determined. It was found that an increase in surface roughness causes an increase in the viscosity of the suspension. Additional resistance to flow could be attributed to internal friction within the suspension due to an increase in the area of contact (during collision or aggregation) among the microspheres, and between microspheres and liquid environment. These findings suggest that the surface geometry of solid particles (e.g., microcapsules, beads, and microspheres) could have a significant effect on the performance of these microparticles in suspension.

Surface phase transition of hydrated calcium oxalate crystal in the presence of normal and stone-formers' urine.

Crystals of calcium oxalate monohydrate (COM), dihydrate (COD) and trihydrate (COT) were grown by slow diffusion of reacting ions from solutions using interfacially controlled crystallization. Phase transition of COT to COD and COM, and COD to COM were studied on single crystal by X-ray diffraction analysis of the same crystal before and after exposure to normal and stone formers' urine. Phase transition on the surface of single crystals has been demonstrated by SEM energy dispersive X-ray microanalysis using windowless detector, and scanning Auger electron microprobe. Data obtained in this study offer direct experimental evidence for phase transformation on the surface of the hydrated calcium oxalate single crystal. In presence of normal urine the surface of COT single crystal undergoes transformation into COD and in presence of recurrent calcium oxalate stone former's urine surface transformation to COM takes place.

Surface studies of calcium oxalate dihydrate single crystals during dissolution in the presence of stone-formers' urine.

Dissolution of calcium oxalate dihydrate (COD) single crystals was studied at different pH levels and in different dilutions of stone formers' (SF) urine. The Fourier descriptors of the contour were determined during dissolution of COD using a quantitative morphological technique. The surface ruggedness of COD single crystals was determined from fractal analysis. The results obtained were compared with COD single crystals behavior in different dilutions of normal urine previously reported. The shape parameters and surface geometry of the dissolving COD crystals were significantly different in normal and SF urine. The data suggest that the shape descriptors and fractal geometry is likely to be a potential factor in identifying the urine of stone formers.

Application of fractal dimension to the study of the surface ruggedness of granular solids and excipients.

This report describes the use of fractal analysis in the study of the surface ruggedness of pharmaceutical solids. A comparison of the fractal dimension of granules and excipients prepared by different techniques revealed a possible correlation between the physical behavior of these granules and their surface geometry. The applications of the proposed tool in the study of the surface geometry of pharmaceutical bulk solids are discussed.

Surface studies of calcium oxalate dihydrate single crystals during dissolution in the presence of urine.

Single crystals of Calcium Oxalate Dihydrate (COD) were grown from solution under controlled release of the reacting ions. Dissolution of COD was studied at different pH levels and in different dilutions of urine. The descriptors of the contour were determined during dissolution of COD using a quantitative morphological technique. The shape parameters and surface ruggedness were determined from Fourier and fractal analysis. The results obtained give quantitative information on the dissolution kinetics and the surface geometry of COD crystals in normal and diluted urine. Dissolution inhibition and morphological changes of COD crystals during dissolution were attributed to selective adsorption of urine non-ionic macromolecules on the crystal stepped surface. Surface etching of COD was found to depend on urine dilution and time of incubation. The data obtained suggest that the geometric structure of the surface is likely to be a potential factor in understanding crystal aggregation in stone formation.

S.E.M. study of urease-induced crystalluria in the presence of hydroxamic derivatives.

The effect of 3 hydroxamic acid derivatives on urease-induced crystalluria was studied in vitro. Acetohydroxamic acid is more effective than salicylhydroxamic and gentisohydroxamic acids in inhibiting the kinetic of urease enzymatic reaction and in retarding the formation of struvite and apatite. Crystal deposits studied by scanning electron microscope (S.E.M.) and X-ray microanalysis indicated that acetohydroxamic acid favours the formation of large crystals of struvite, and less aggregation is observed. Salicyl and gentiso derivatives favour the formation of brushite together with struvite and apatite.

Tack behavior of coating solutions III.

The effect of finely divided solids on the tackiness of coating solutions was determined using a parallel-plate technique. Results demonstrated that the tackiness of coating solutions containing relatively low concentration of polymers augments with the increase in concentration and diminishes with the increasing particle size of finely divided solids. In contrast, the tackiness of coating solutions containing high concentrations of polymers is suppressed upon increasing the concentration and decreasing the size of finely divided solids.

The effect of pH and urine dilution on the electrophoretic mobility of uric acid crystals.

As a result of a continuing programme to understand better the uric acid stone treatment and prophylaxis, an investigation of the effect of pH and urine dilution on the surface charge of uric acid crystals was undertaken. A microelectrophoretic technique was employed to characterize the nature of the surface charge and the electrokinetics of uric acid crystals both in natural and synthetic urines under different conditions of pH and dilution. Both dilution and alkalization reduced the specific conductance of urine and increased the electrophoretic mobility (zeta potential) of uric acid crystals. The presence of cationic additives in diluted urine altered the zeta potential of uric acid crystals. Such findings suggest that proper control of the pH level and urine dilution as well as the surface charge at the solid-liquid interface represent an important factor in the uric acid stone prophylaxis.

Tack behavior of coating solutions II.

The tackiness of coating solutions containing high concentrations of polymers was determined using a parallel plate technique. Kinematics of the film-splitting process was also investigated using a high-speed movie camera. The results showed that the impulse required to split a liquid film of highly concentrated polymer solution (semisolid), in contrast to a dilute solution is related not to viscosity, but to the internal structures of the system. Evidence has been found that the materials that are considered to be tacky in practice, display "delayed elastic effects" and require far larger impulses than nontacky materials.

Calcium oxalate crystal growth in normal urine: role of contraceptive hormones.

Oral contraceptives inhibited the growth of calcium oxalate crystals in female urine, and the growth rate inhibition depended on the dose of ethinyl-oestradiol in the oral contraceptive agent. The results suggest that the crystallization kinetics of calcium oxalate in urine could be under the control of oestrogenic hormones by an unidentified mechanism.

PIP: The crystallization kinetics of calcium oxalate was studied in the urine of males, females, and females on oral contraceptives (OCs), for the determination of the crystal growth rate under defined experimental conditions that could offer possible clues as to the role of estrogenic hormones in calcification. 49 subjects on an uncontrolled diet participated. 12 female subjects received OCs as combination tablets containing 0.03 mg or 0.05 mg ethinyl estradiol with 1 mg progestin. The urine sample was taken before lunch. Total calcium concentration and pH were determined immediately for each urine sample. All samples were within the normal physiological limits and in accordance with the recently reported circadian rhythm for normal subjects at this period of the day. There was no significant difference between the median volume diameter D50 of calcium oxalate crystals grown in the urine of males and in the urine of females. There was a significant difference (PL 0.05) between the median diameter of the crystals grown in the urine of females on OCs and controls. The determination of the uniformity factor that provides a measure of the uniformity of distribution indicates that the size distribution of the crystals has not been affected by estrogenic hormones. The calcium oxalate crystal growth rate in the urine of females was not significantly different from that obtained in the urine of the male. The relatively higher coefficient of variation for the female group (68.8%) versus the male group (42%) could be attributed to the variations in the concentration of urinary excreted estrogens during the different phases of the menstruation cycle, but the intake of OCs produced a remarkable and significant retardation of the growth rate of calcium oxalate crystals in the urine of female subjects. Growth inhibition increased with an increase in the dose of the estrogenic hormone in the OC tablet. The 0.05 mg ethinyl estradiol tablet exerted a higher inhibitory effect than the 0.03 mg dose. On the basis of these preliminary results, one can speculate that estrogen hormones and/or their metabolites may play a key role in the formation of calcium oxalate crystals in the urinary tract.

Size-shape analysis of calcium oxalate crystals in the study of stone formation.

In renal stones very little is known about the relationships between size-shape parameters of the particles and packing arrangement. Factors such as the distance travelled by the deposited crystal, the residence time and fluid flow are believed to be important in modifying the distribution of size and the morphological characteristics of the mineral phase. This paper reviews some experimental studies on the growth of calcium oxalate crystals under different growth conditions. The crystals grown in aqueous media, gel systems, rat-kidneys, and in renal stones were studied by scanning electron microscope (SEM). Size distribution parameters, shape factors and distribution of shape were determined in stones using the SEM and image analysis system. Particle size and particle morphology analysis may provide unique information in the study of stone genesis, difficult to obtain by other methods.

Growth and characterization of calcium oxalate dihydrate crystals (weddellite).

Conditions are given for the growth of calcium oxalate dihydrate crystals (weddellite) in aqueous solution. The crystals obtained were characterized by scanning electron microscopic, spectroscopic, and thermal methods. The dissolution kinetics and electrophoretic mobility were determined; the thermodynamically unstable calcium oxalate dihydrate had a higher dissolution rate and a lower zeta potential than the monohydrate and underwent a phase transformation into the more stable calcium oxalate monohydrate. The results obtained on the chemical stability and the surface charge of calcium oxalate dihydrate offered additional information for assessing the current theories on the formation of calcium oxalate renal stones.