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PubMed2004

[The expression of growth hormone release factor gene carried with PLGA microspheres in muscle tissue and its effect on mouse growth].

Injectable sustained-release pcDNA3-GRF (1-32) microspheres were prepared by double emulsion-in liquid evaporation process,using biodegrable poly lactic-co-glycolic acid as carrier. The enrapment efficiency, mean particle size, drug content thus prepared were 69%, 2.20 microm, 8% and 70% respectively. The result of transfection in vivo showed that after 30 days, accumulative increased body weights on the group injected with pcDNA3-GRF (1-32) microspheres was significantly higher than those group injected with naked plasmid (12.87%), plasmid-empty microspheres (19.72%) and saline (58.58%) respectively. PCR and RT-PCR showed that the expression level of GRF gene on the group injected with pcDNA3-GRF (1-32) microspheres was the highest. GRF gene released by microspheres was still detected after 30 days. In conclusion, pcDNA3-GRF (1-32) microspheres have a controlled release effect and GRF gene could be successfully transfected into muscle cells of mouse by microspheres with higher efficacy and stronger biological function.

Animals↗
PubMed2005

Dielectrophoresis-based 'Lab-on-a-chip' devices for programmable binding of microspheres to target cells.

There is a general agreement on the fact that the Laboratory on chip (Lab-on-a-chip) technology will enable laboratory testing to move from laboratories employing complex equipments into non-laboratory settings. In this respect, dielectrophoresis (DEP) is a very valuable approach to design and produce Lab-on-a-chip devices able to manipulate microparticles and cells. In this study, we report the application of DEP-based devices for facilitating programmable interactions between microspheres and target tumor cells. We used two Lab-on-a-chip devices, one (the SmartSlide) carrying 193 parallel electrodes and generating up to 50 cylinder-shaped DEP cages, the other (the DEP array) carrying 102,400 arrayed electrodes and generating more than 10,000 spherical DEP cages. We determined whether these devices can be used to levitate and move microspheres and cells in order to obtain a forced interaction between microspheres and target cells. The first major point of this manuscript is that the DEP-based SmartSlide can be used for transfection experiments in which microspheres and target cells are forced to share the same DEP cage, leading to efficient binding of the microspheres to target cells. The data obtained using the DEP array show that this system allows the sequential, software-controlled binding of individually and independently moved single microspheres to a single target tumor cell. To our knowledge, this is the first report on the possible use of a DEP-based Lab-on-a-chip device for guided multiple binding of singularly moved microspheres to a single tumor cell. This approach can be of interest in the field of drug discovery, delivery and diagnosis.

Algorithms↗
PubMed2006

[Experimental research on establishing chronic ischemic heart failure model of minipig with intracoronary perfusion of plastic microspheres by catheterization].

OBJECTIVE: To establish a stable chronic ischemic heart failure (CIHF) model of minipig caused by gradual myocardial ischemia and necrosis that was achieved with repetitive microspheres perfusion in left anterior descending artery (LAD). METHODS: A total of fifteen Wuzhishan minipigs original in Hainan China (8 to 11 months old with body weight of 20 to 30 kg) were used. The 4F angiographic catheter was superselectively engaged in LAD, and 1 ml of suspending plastic microspheres fluid were given repeatedly at ten-minute intervals, which include microspheres 1.0 x 10(5)/ml, until LVEDP raising and maintaining from 15 mm Hg to 18 mm Hg and TIMI flow was less than or equal to grade 2. Electrocardiography, hemodynamic parameters, CK-MB and cTnT were monitored during the procedure. LVEF was repeatedly measured with ultracardiography at 10 d, 20 d, 30 d, 40 d, 50 d, 60 d after establishing chronic ischemic heart failure model. Meanwhile, hemodynamic indices including mRAP, mRVP, mPAP, PCWP and CO (thermo-dilution method) were measured before and two months after procedure. The success rate, stability and repetition of chronic ischemic heart failure model were identified and evaluated. Finally, myocardial infarcted area was measured and myocardial pathologic examination was investigated. RESULTS: Eleven minipigs survived two months after procedure. There were ten minipigs accorded with the criteria (LVEDP > 18 mm Hg CO reduced by 30%) of the CIHF model and the success rate was 66.7% with a mean of 3.2 +/- 0.9 times of microspheres injections and total doses of (3.2 +/- 0.9) x 10(5) microspheres. This resulted in 38.5% reduction in LVEF, 197.8% elevation in LVEDP and 46.8% declining in CO from baseline values (P < 0.01), while mRAP, mRVP, mPAP and PCWP increased significantly as compared with those before procedure. Cross myocardium pathology showed the ratio of necrosis area to left ventricle (LV) area was 25.4% - 34.9% (mean 28.6%) and light microscopy examination of LV myocardium revealed that intravascular semitransparent plastic microspheres distributed throughout subendocardium of left ventricular anterior and apical parts, with more numerous focal myofiber necrosis, which characterized by pathologic founding of ischemic necrosis of myocardium with fibre proliferation. CONCLUSION: A stable CIHF model could be established in Chinese Wuzhishan minipigs with intra-coronary microspheres perfusion via superselectively engaging in LAD, which was prior to those of drug-induced, tachycardia-pacing induced or coronary artery ligation-induced, and had the advantages of stability, closed chest, mild trauma higher success rate and easy for repetition. It might be suitable for using the research of CIHF as large reliable experimental animal model.

Animals↗
PubMed1990

[Intravitreal drug delivery by microspheres of biodegradable polymers].

We evaluated the efficacy of microspheres of biodegradable polymers as a slow releasing drug delivery system in the vitreous body. Microspheres containing 5-FU were prepared with polymers of poly-(lactic acid) or copolymers of glycolic acid and lactic acid. The release of the drug was studied in vitro. Poly-(lactic acid) microspheres released 5-FU for 7 days. The intravitreal kinetics of the microspheres was studied in rabbits in vivo. The microspheres disappeared from the vitreous cavity of normal eyes by 48 +/- 5 days after injection. Disappearance was accelerated from the vitreous cavity of vitrectomized rabbits (14 +/- 2 days, p less than 10(-6)). No abnormality was found on electroretinographic or histological examinations after microspheres injection. These results suggested that microspheres of biodegradable polymers could be useful as a potential drug delivery system for sustained drug release in the vitreous body.

Animals↗
PubMed1975

Comparison of gastric mucosal blood flow as determined by aminopyrine clearance and gamma-labeled microspheres.

Gastric mucosal blood flow was simultaneously determined by aminopyrine clearance and gamma-labeled microspheres (15 +/- 5 mu in diameter) in anesthetized dogs prepared with a chambered segment of stomach greater curvature. Paired flow measurements were made in 11 dogs (n = 28) secreting in response to intravenous histamine (1mug per kg per min), in 11 (n = 21) nonsecreting dogs given intravenous isoproterenol (0.5 or 1.0 mug per kg per min), and in 9 (n = 10) dogs given no drugs to stimulate secretion or blood flow (resting dogs). Eight additional injections were done in dogs receiving various combinations of isoproterenol and histamine. Isotonic HCl was maintained on the mucosal surface during all experiments. Regression analysis demonstrated a highly significant linear correlation between clearance and microsphere-measured flow in the histamine (P less than 0.001, r = 0.96) and isoproterenol (P less than 0.001, r = 0.78) experiments, with clearance averaging 83% of microsphere flow during histamine stimulation but only 25% during isoproterenol. The relationship between clearance and microsphere flow was not significantly different for the resting and isoproterenol experiments. Mucosal perfusion measured by microspheres was about 5 times the resting value for both histamine and isoproterenol-stimulated dogs. Perfusion calculated from aminopyrine clearance averaged 46, 38, and 90% of the microsphere value in the resting, isoproterenol, and histamine experiments, respectively. Pooled data from secreting dogs demonstrated a fairly constant ratio of microsphere-measured flow to clearance (1.25 +/- 0.06 mean +/- SEM), regardless of the secretory rate. Our results indicate that aminopyrine clearance reflects only a small fraction of mucosal blood flow in the nonsecreting stomach, even in the presence of exogenous acid.

Aminopyrine↗
PubMed1984

Distribution of microspheres in the brain of hypertensive rats.

The blood perfusion of different parts of the brain tissue was examined by means of microspheres 15 and 50 micron in diameter, in normotensive control rats and in animals with experimental renovascular hypertension. The microspheres were labelled with fluorescein isothiocyanate and their numbers in the tissue were determined in consecutive histological sections by UV microscopy. In the control rats, the incidence of wedged microspheres per 1 mm3 tissue was high in the cerebellum, cerebral cortex, subcortical tissue and pons Varolii, but low in the thalamic and hypothalamic regions, indicating that these parts were relatively poorly perfused with blood. The significantly greater accumulation of microspheres in the cortex and subcortical tissue of hypertensive rats seems to have been due to hypertensive narrowing of the arterioles. Conversely, the diminished incidence of microspheres in the thalamus and hypothalamus may have been due partly to microsphere trapping in the narrowed upstream blood vessels and partly to thinning of the capillary network. Total microsphere recovery in the brains of the control and the hypertensive rats was almost identical, implying that only the distribution of brain blood perfusion is altered in experimental hypertension.

Animals↗
PubMed1994

Application of epirubicin containing albumin microspheres in the experimental therapy of breast cancer.

In the experiment we attempted to use albumin microspheres as carriers of cytostatics to acquire a higher drug concentration in the tumor for a longer time. It was expected that the efficiency of a treatment with a microsphere-entrapped epirubicin would be better than a treatment with microsphere-free drug. Albumin microspheres containing epirubicin were prepared by ultrasonic homogenization in oil and heat denaturation. In vitro experiments and the test for biological activity on human breast carcinoma cells implanted into Nu/Nu mice were carried out. Growth of tumors in the group of mice treated with microsphere-entrapped epirubicin was inhibited more effectively in comparison with growth of tumors in the group treated with microsphere-free drug. These results suggest that the change of the drug form can enhance antitumor effect of epirubicin and that albumin microspheres are suitable drug carriers.

Animals↗
PubMed1994

Physical and biochemical characterization of Albunex, a new ultrasound contrast agent consisting of air-filled albumin microspheres suspended in a solution of human albumin.

Albunex is a new ultrasound contrast agent for medical imaging. The product consists of air-filled albumin microspheres suspended in a solution of 5% (w/v) human albumin. The suspension is sterile, non-pyrogenic and isotonic, with a pH of 7.0 and a viscosity of 1.4 relative to water. The contrast effect is caused by the air-filled microspheres, which range in diameter from 1 to 15 microns, with less than 5% being larger than 10 microns. The product contains a total of about 7 x 10(8) microspheres/ml of suspension. The number concentration of microspheres with diameters between 4 and 10 microns is about 2 x 10(8)/ml. The latter microsphere fraction is assumed to give the main contribution to the ultrasound signal in the left ventricle of the heart after intravenous injection. The air-filled microspheres are prepared by sonication of a heated solution of 5% (w/v) human albumin. During the sonication process, microbubbles of air are formed which become encapsulated in a thin shell of aggregated albumin about 15 nm in thickness. Due to the stabilizing effect of the albumin shell, the air-filled microsphere suspension is stable for at least 2 years when stored refrigerated. The microsphere protein represents about 1.5% of the total protein in the suspension. The remaining protein is soluble albumin molecules which behave like the albumin molecules in the starting material when analysed by a number of biochemical techniques.

Albumins↗
PubMed1993

Use of fluorescent latex microspheres to measure coronary blood flow distribution.

Radioactive microspheres have long been in use to measure blood flow distribution to various vascular beds. Their drawbacks are the short half-lives of the radioactive material, the need for appropriate care in handling and disposing of such material, and their relative expensiveness. We investigated the use of fluorescent microspheres as indicators of coronary blood flow distribution in a canine model. Radioactive (125I) microspheres were used as a comparison standard. Four colors of fluorescent microspheres were used: blue, yellow-green, orange, and red, having emission frequencies ranging from 385 to 605 nM. The experiments were carried out in dogs under pentobarbital anesthesia, in which the microspheres were given during pump perfusion of the left circumflex artery with the animal's own blood. The hearts were removed, fixed for 3 days in 10% formalin, and sectioned. Samples from the endocardial, myocardial, and epicardial layers were read on a gamma counter. The fluorescent microspheres were extracted from the same tissues into ethyl acetate, and read in a fluorescence spectrophotometer at the appropriate excitation/emission frequencies. Comparable results were obtained from the two methods, with good sensitivity and resolution of dye colors, using the fluorescent microspheres.

Animals↗
PubMed1993

[Study on albumin microspheres as drug carrier for liver targeting].

In this paper 6 factors and 12 levels of each variable were selected by Uniform Design Method and computer for preparing albumin microspheres with emulsion-chemical cross-linking. An optimal procedure for preparing albumin microspheres was established and the mean diameter of albumin microspheres is 0.41-0.47 micron. Albumin was labelled with 125I-isotope and 125I-albumin microspheres were prepared according to the optimal procedure. The suspension of 125I-albumin microspheres with 0.1% Tween-80 saline was injected via mice tail vein. The animals were sequentially killed and the radioactivity of blood, spleen, liver, kidney, stomach, heart, lung, thyroid and brain were measured. The results showed that albumin microspheres were accumulated mainly in the liver, about 68% of the injected dose at the peak concentration. The pharmacokinetics of albumin microspheres in liver was also studied and two-compartmental model can be used to describe the regulation.

Animals↗
PubMed1996

Structure and organization of albumin molecules forming the shell of air-filled microspheres: evidence for a monolayer of albumin molecules of multiple orientations stabilizing the enclosed air.

The structure and organization of albumin molecules in the shell of air-filled microspheres formed by sonication of a 5% albumin solution have been investigated. By limited proteolysis of intact microspheres, it has been shown that every albumin molecule in the shell may be cleaved without disintegration of the microsphere structure. The microsphere shell accordingly appears to be composed of a monolayer of albumin molecules. Most of the main cleavage sites identified after N-terminal sequencing of proteolytic fragments are localized in three distinct regions common to both native and microsphere albumin molecules: the extended region of the first domain, the extended region of the second domain and the first disulphide loop of the third domain. The similarity in the localization of cleavage sites in the native and microsphere albumin molecules suggests that the formation of microspheres implies only a limited degree of conformational change of the albumin molecules. The localization of the cleavage sites in the three-dimensional structure of albumin suggests that the shell may be constituted of albumin molecules in both a native-like heart-shaped form and a more flipped-out elongated form with different orientations.

Air↗
PubMedDate not supplied

Beneficial effect on nebracetam on energy metabolism after microsphere-induced embolism in rat brain.

The present study was undertaken to examine the possible therapeutic effects on nebracetam on the energy metabolism of rat brain regions in microsphere-induced, sustained ischemia. Microsphere embolism was induced by injection of 900 microspheres (48 microns in diameter) into the right internal carotid artery of rats, and changes in the energy metabolism of the cerebral cortex, striatum and hippocampus of the right hemisphere were determined without and with nebracetam treatment. Microsphere embolism induced increases in lactate and glucose contents and decreases of ATP and creatine phosphate contents in these regions, suggesting that sustained impairment of cerebral energy metabolism occurred. These changes were gradually reversed with time after the operation. Treatment of microsphere-injected rats with 30 mg/kg of nebracetam, p.o., twice a day, was started one day after the onset of cerebral ischemia. The effects of treatment with nebracetam on cerebral energy metabolites were determined on the 3rd and 7th day after operation. Treatment of microsphere-injected rats with nebracetam significantly improved these variables on the 3rd day after the onset of ischemia, but the improvement was small on the 7th day, except for reversal of the hippocampal ATP content. These results suggest that nebracetam is a possible therapeutic agent for the restoration of cerebral energy metabolism against microsphere-induced, sustained cerebral ischemia.

Adenosine Triphosphate↗
PubMed1998

[A study on accuracy of rCBF measurements loaded with acetazolamide based on the microsphere model using iodine-123-IMP SPECT].

We studied the accuracy of the method for measuring regional cerebral blood flow (rCBF) loaded with acetazolamide based on the microsphere model using iodine-123-IMP (IMP) SPECT. Two methods were examined, the super-early microsphere method with continuous withdrawal of arterial blood using the SPECT image obtained 5 min after tracer injection and the early microsphere method with one-point arterial sampling using the SPECT image obtained 30 min postinjection. On five subjects, after acetazolamide administration we measured rCBF by the analysis based on the two-compartment model using the data derived from dynamic SPECT scans and the sequential arterial blood sampling after IMP injection. Values of rCBF obtained by both super-early microsphere method and early microsphere method were significantly correlated with those obtained by the two-compartment model analysis (r = 0.982, 0.930, respectively). We conclude that it is possible to use the method based on the microsphere model in measuring rCBF loaded with acetazolamide. The early microsphere method with one-point sampling should be used clinically because of its simplicity and less-invasiveness.

Acetazolamide↗
PubMed1998

Classification and properties of 64 multiplexed microsphere sets.

We describe a practical method for the analysis of multiple analytes in a single sample. The vehicle for each separate measurement consists of a set of microspheres identifiable by characteristic fluorophores embedded in the particles. The use of robust, bench-top flow cytometers (flow microfluorimeters) for the analysis of the multiple sets of microspheres is facilitated by hardware and software, which acquire the data from the cytometer, classify the microspheres according to sets, and collate measurement information from each microsphere set in real time. This measurement system can analyze up to 64 analytes in a single sample. The advantages of multiplexed assays using flow cytometry include robust measurements, because each microsphere set is measured repeatedly. The advantage of the assay's is consistent with simultaneous measurement of many parameters as well as the speed with which the flow microfluorimeter (cytometer) makes measurements (many hundreds per second). Here, we describe the properties of the microspheres, the calibration of the cytometer, and the influence of the properties of the microspheres on the sensitivity of measurements.

Calibration↗
PubMed1998

Intratumoral injection of rhenium-188 microspheres into an animal model of hepatoma.

UNLABELLED: Intratumoral injection of 90Y microspheres is a potential alternative in the treatment of primary liver tumor. However, complicated preparation and lack of a gamma ray for imaging are the disadvantages of 90Y. In this study, we used 188Re, a generator-produced radioisotope with 155-keV gamma ray emission, to label microspheres. After intratumoral injection of 188Re microspheres into rats with hepatoma, biodistributions and survival times were analyzed. METHODS: Twelve male rats with hepatoma were killed at 1, 24 and 48 hr (4 rats at each time point) after intratumoral injection of approximately 7.4 MBq 188Re microspheres. Samples of various organs were obtained and used to calculate the tissue concentrations. In addition, 30 male rats bearing hepatoma were divided into two groups (15 rats in each group) to evaluate survival time. Group 1 received intratumoral injection of 37 MBq 188Re microspheres, whereas Group 2 served as the control group and received an intratumoral injection of 0.1 ml normal saline only. Survival time was calculated from the day of injection to 2 mo after treatment. RESULTS: Radioactivity in the tumor was very high throughout. Biological half-time was 170.8 hr. Radioactivity in the lung was 1.78% injected dose (i.d.)/g at 1 hr but declined rapidly over time. The concentration in the urine was approximately 6.14% i.d./ml after the first hour and rapidly declined thereafter. The concentrations of radioactivity in other organs, such as normal liver, muscle, spleen, bone, testis and whole blood, were quite low throughout the study. Twelve of 15 (80%) of rats survived over 60 days after intratumoral injection of 188Re microspheres, whereas only 4 of 15 (26.7%) survived more than 60 days after injection of normal saline only. The difference between the groups was significant (p < 0.05). CONCLUSION: Rhenium-188 offers cost-effectiveness, on-site availability, short half-life, energetic beta particle, emission of gamma photons for imaging, easy preparation, easy clinical administration and apparent lack of radiation leakage from the treated tumor. Direct intratumoral injection of 188Re microspheres is extremely attractive as a clinical therapeutic alternative in hepatoma patients.

Animals↗
PubMed1996

[Studies on oral sustained-release microspheres of nifedipine].

Nifedipine has been incorporated into Eudragit RL microspheres by the emulsion solvent-evaporation process using an acetone/liquid paraffin system. The drug in the Eudragit RL microspheres was present in either molecular dispersion or amorphous state. The drug release profile from microspheres conformed to the Higuchi equation. The microspheres were stable under different storage conditions for six months with respect to drug content, dispersing state and release profile. The in vivo results in eight healthy volunteers showed that the relative bioavailability of the nifedipine sustained-release microspheres against commercial retard tablet as a control was 102.5%, and the microsphere formulation was bioequivalent to the retard tablet. Significant in vitro and in vivo correlation was also found for the microspheres.

Adult↗
PubMed2000

Dependence of Temperature-Sensitivity of Poly(N-isopropylacrylamide-co-acrylic acid) Hydrogel Microspheres upon Their Sizes.

Monodisperse poly(N-isopropylacrylamide-co-acrylic acid) hydrogel microspheres were prepared by a membrane emulsification method using membranes of pore diameters of 0.33, 0.73, 1.15, and 1.70 µm. The hydrogels were synthesized by polymerization of 3.6 M N-isopropylacrylamide (N-IPAAm or NIPAM) and 0.4 M acrylic acid (AAc). Their surface properties were studied by measuring the electrophoretic mobility of the microspheres in electrolyte solutions at pH 7.4 at 25, 30, 33, 35, 40, and 45 degrees C. Poly(N-IPAAm-co-AAc) microspheres have shown negative mobility. More negative values of electrophoretic mobility were obtained with the smaller microspheres than the larger ones at each temperature. The surface charge density of the microspheres increased and their surfaces became harder above 35 degrees C, since the microspheres contained thermosensitive poly(N-IPAAm) moiety and LCST increased by the addition of AAc, while that of poly(N-IPAAm) was 33 degrees C. It has recently been found that the smaller microspheres exhibit the stronger dependence of both surface charge density and softness on the temperature. Copyright 2000 Academic Press.

Journal Article↗
PubMed1997

Protein delivery from biodegradable microspheres.

The key components to the successful development of a biodegradable microsphere formulation for the delivery of proteins are polymer chemistry, engineering, and protein stability. These areas are intricately related and require a thorough investigation prior to embarking on the encapsulation of proteins. While each of these components is important for the development of a biodegradable microsphere formulation for protein delivery, other critical issues should also be considered. In particular, preclinical studies in the appropriate animal model are usually necessary to assess the potential feasibility of a continuous-release dosage form. These studies should be performed at the earliest possible stage of development to validate the feasibility of a controlled release formulation. After the utility of a controlled release formulation has been demonstrated, the polymer matrix should be chosen and bench-scale production of microspheres initiated. The only polymers presently approved for human use for controlled delivery are the polylactides [poly(lactic acid), poly(glycolic acid), and poly(lactic-coglycolic) acid]. These polymers require multiphase processes involving several steps to produce microspheres containing the desired protein. A thorough review of previous work on encapsulation with these polymers should provide some insight into conditions to be assessed in developing a process. Once a process is chosen, it must be optimized to provide the highest possible yield of microspheres with the desired characteristics (e.g., loading, release, size, etc.). Finally, the final aseptic process should be validated and methods generated to assess the final product. The clinical studies should then start upon approval of the IND application. In the future, the biotechnology industry, and the pharmaceutical industry in general, will be seeking new methods to improve the delivery of therapeutic agents such as proteins and peptides. Formulations like biodegradable microspheres significantly reduce health-care costs since fewer administrations are needed, and they provide a competitive advantage in markets with several competing products (e.g., LHRH agonist market). Further, many new indications such as neurological diseases may require a long-term delivery system. The future success of biodegradable microsphere formulations will primarily depend on the commitment of the pharmaceutical and biotechnology industries to the development of this technology.

AIDS Vaccines↗