[New markers in lung scanning. (Iodine-13- albumin microspheres, Technetium-99m albumin microspheres, Indium-113m microspheres, Indium-113 iron hydroxide)].
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Humans↗
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Preparation of enteric-coated microspheres of Mycoplasma hyopneumoniae vaccine with cellulose acetate phthalate: (II). Effect of temperature and pH on the stability and release behaviour of microspheres.
The in vitro stability (temperature and pH) and dissolution study (pH 7.4 phosphate buffer solution and pH changed medium) of the enteric-coated microspheres containing Mycoplasma hyopneumoniae vaccine (MHV) were examined. The MHV microspheres were thermally more stable than the unencapsulated MHV. More than 90% of antigenicity was retained in the MHV microspheres for 3 weeks when stored at 4 degrees C. The MHV microspheres in pH 1.2 and pH 3.0 medium were more stable than the unencapsulated MHV. The MHV enteric-coated microspheres exhibited an excellent enteric function to prevent pH-related inactivation. The influence of particle size, CAP concentration and span 80 concentration on the MHV released from microspheres was also determined. The smaller the particle size, the higher the dissolution rate due to the larger surface area of the smaller particle. The higher the concentration of span 80 used, the more the greater the amount of MHV released. This was attributed to the more porous structure of microspheres prepared by the higher concentration of span 80. By increasing the CAP concentration, however, the release rate of MHV was decreased due to the larger amount of CAP and the more compact structure of microspheres.
Animals↗
In vitro release profile of mitomycin C from albumin microspheres: extrapolation from macrospheres to microspheres.
To analyze the in vitro release profiles of mitomycin C from albumin microspheres prepared by chemical denaturation in a multiparticulate system, a method to calculate the total cumulative amount of mitomycin C released from a batch of microspheres was developed. Mitomycin C-loaded albumin macrospheres (diameter in mm range) were prepared, and the in vitro release kinetics of mitomycin C from individual macrospheres were determined. Then the relationship between the kinetic parameters and the physical parameters (e.g., diameter, weight) was investigated under the assumption that macrospheres and microspheres behave identically. Further, the size distribution of microspheres was measured, and the total cumulative amount of mitomycin C released from albumin microspheres was calculated. The release profiles of mitomycin C from individual macrospheres fitted first-order release kinetics better than spherical matrix kinetics. The calculated initial mitomycin C contents and first-order release rate constants for individual macrospheres were correlated with the weight and reciprocal of surface area of the macrospheres, respectively. The observed in vitro release profile for the microspheres agreed with the calculated values. These results suggest that this method is valid for calculating drug release from albumin microspheres.
Albumins↗
Polyglutaraldehyde: a new reagent for coupling proteins to microspheres and for labeling cell-surface receptions. II. Simplified labeling method by means of non-magnetic and magnetic polyglutaraldehyde microspheres.
Procedures were developed for the synthesis of a new immunoreagent in form of polyglutaraldehyde (PGL) microspheres in sizes ranging from about 50 nm to 1.5 micron. Addition of fluorochromes during synthesis yielded microspheres of high fluorescence intensity. By carrying out the polymerization of glutaraldehyde in presence of iron oxide, magnetic PGL microspheres were produced. Antibody conjugates obtained by interaction of PGL microspheres with immunoglobulins were used to label human red blood cells (RBC) and lymphocytes. A simple method for the separation of magnetically labeled human RBC from unlabeled cells was demonstrated.
Aldehydes↗
Poly(L-lactic acid) microspheres containing neutron-activatable holmium-165: a study of the physical characteristics of microspheres before and after irradiation in a nuclear reactor.
The solvent evaporation technique was employed to prepare poly(L-lactic acid) (PLA) microspheres with 165Ho acetylacetonate (Ho-AcAc). Particle size, percentage Ho-165, percent residual solvent, and retentive ability of the spheres were found to be strongly affected by preparatory conditions. Differential scanning calorimetry (DSC) thermograms suggested that the Ho-AcAc existed in the PLA matrix as a molecular dispersion. High neutron flux irradiations of the PLA spheres in a nuclear reactor produced Ho-166, a therapeutic radionuclide that emits high-energy negatrons (Emax = 1.84 MeV; half-life = 26.9 hr). The gamma radiation dose (53-75 Mrad) from the core of the reactor provided an overkill of all bioburdens in the PLA spheres. Gel permeation chromatography (GPC) analysis showed that these irradiations caused a reduction in PLA molecular weight. Infrared spectra, 13C NMR spectra, 1H NMR spectra, and DSC thermograms further confirmed the presence of lower molecular weight PLA but proved the overall maintenance of PLA structure.
Bacillus↗
Drug-carrier property of albumin microspheres in chemotherapy. I. Tissue distribution of microsphere-entrapped 5-fluorouracil in mice.
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Albumins↗
Drug-carrier property of albumin microspheres in chemotherapy. II. Preparation and tissue distribution in mice of microsphere-entrapped 5-fluorouracil.
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Animals↗
Polymer-coated albumin microspheres as carriers for intravascular tumour targeting of cisplatin.
We used a poly-lactide-co-glycolide polymer (PLAGA 50:50) to formulate cisplatin (cDDP) into microspheres designed for intravascular administration. Two systems were developed. PLAGA-coated albumin microspheres and microspheres consisting of PLAGA only. PLAGA-coated microspheres displayed a mean diameter of 31.8 +/- 0.9 microns and a payload of 7.5% cDDP (w/w). Solid PLAGA microspheres exhibited a mean diameter of 19.4 +/- 0.6 microns and a payload of 20% cDDP. Release characteristics and in vitro effects on L1210 leukemia and B16 melanoma cell lines were investigated. Both types of microsphere overcame the initial rapid release of cDDP (burst effect), and PLAGA-coated albumin microspheres also showed a lag phase of approximately 30 min before cDDP release began. PLAGA-coated albumin microspheres released most of their payload through diffusion, and the coating eventually cracked after 7 days' incubation in saline supplemented with 0.1% Tween at 37 degrees C, enabling the release of any cDDP remaining. Effects of platinum, pre-released from PLAGA-coated albumin microspheres on the in vitro growth of L1210 cells were comparable with those of standard formulations (dissolved) of cDDP. Material released from non-drug-loaded PLAGA microspheres had no effect on L1210 cell growth, suggesting the absence of cytotoxic compounds in the matrix. The colony-forming ability of B16 cells was also equally inhibited by standard cDDP and pre-released drug. These studies show that formulation of cDDP in PLAGA-based microspheres prevents the rapid burst effect of cDDP seen in previous preparations and offers an improved system of administration for hepatic artery infusion or adjuvant therapy, enabling better clinical handling and the promise of a higher ratio of tumour tissue to normal tissue.
Animals↗
The effect of ergotamine on tissue blood flow and the arteriovenous shunting of radioactive microspheres in the head.
1 The radioactive microsphere method was used to study the effects of ergotamine (5, 10 and 20 mug/kg, i.v.) on systemic and regional haemodynamic variables in chloralose-urethane anaesthetized cats. The influence of the drug was also studied on the number of 15 mum microspheres escaping entrapment in the head to emerge in the left external jugular vein.2 Ergotamine decreased the heart rate and cardiac output. Since arterial blood pressure remained unchanged, calculated total peripheral resistance increased.3 The regional distribution of cardiac output obtained with 15 mum microspheres agreed well with previous studies in cats where 25 mum spheres were used. The most pronounced difference was that in the present investigation more microspheres, apparently escaping through arteriovenous anastomoses (AVAs), were detected in the lungs than when larger spheres had been used.4 Coronary blood flow decreased, while uterine blood flow was increased by the drug. The microsphere content of the lungs, which receive the spheres not only via bronchial arteries but also via AVAs, was greatly reduced by all doses of ergotamine. Ergotamine did not influence tissue blood flow to other major organs such as the brain, kidneys, skin, liver, skeletal muscle or the gastrointestinal tract.5 In the 16 experiments, 0.46 +/- 0.05 (s.e. mean)% of the total microspheres injected (equivalent to 11.7 +/- 1.4% of microspheres detected in the left-side of the head) appeared within 2 min of microsphere injection into the left external jugular vein. The highest dose of ergotamine significantly reduced the shunting of the microspheres in the head.6 Since 15 mum microspheres are only likely to reach the lungs by passing into the venous circulation through large glomus-type AVAs, we conclude that ergotamine reduces the fraction of microspheres appearing in the lungs by causing strong vasoconstriction in the AVAs in the head.7 In conformity with the closure of head AVAs is the finding that ergotamine reduced the jugular venous Po(2) and O(2) saturation thereby increasing the A-V O(2) saturation difference.8 It is quite possible that decreased A-V shunting may be the prominent mechanism of the antimigraine action of the drug, since sudden opening of AVA's has been implicated in the pathophysiology of migraine-syndrome.
Animals↗
Evaluation of biodegradable microspheres as vaccine adjuvant for hepatitis B surface antigen.
Biodegradable microspheres were evaluated as vaccine adjuvants based on their ability to provide prolonged release of incorporated agents. Hepatitis B surface antigen (HBSA) prepared by recombinant DNA technology was chosen as a model antigen and encapsulated into polyglycolic acid (PGA) by solvent extraction and solvent evaporation techniques. Five microsphere formulations were prepared to evaluate effect of microsphere size and the presence of immunostimulants such as muramyl dipeptide (MDP) or aluminum hydroxide. The microspheres were characterized for size distribution, surface morphology and antigenicity. Guinea pigs were chosen as the animal model for evaluation of antigenicity of the formulations. The animals were divided into seven groups of four animals each and the microsphere formulations were injected intraperitoneally, using alum adsorbed HBSA as positive control and placebo microspheres as negative control. Blood samples were withdrawn from the animals by toe clipping at two, four, six and sixteen weeks and plasma was analyzed for antibodies against hepatitis B by an enzyme linked immunoassay. At sixteen weeks, the animals were reinjected and evaluated for antibody response at two, four and six weeks post second injection. Antibody response to the microspheres was higher than control. Smaller size microspheres elicited earlier antibody response while the larger size microspheres provided delayed and longer duration of antibody production. Microspheres with MDP potentiated the antibody response. The results demonstrate the applicability of biodegradable microspheres for immunization against hepatitis B.
Adjuvants, Immunologic↗
Microspheres of biodegradable polymers as a drug-delivery system in the vitreous.
Microspheres of biodegradable polymers were evaluated as a potential controlled-release drug-delivery system in the vitreous. The microspheres were prepared with polymers of poly(lactic acid) or copolymers of glycolic acid and lactic acid. The release of 5-fluorouracil (5-FU) from the microspheres was studied in vitro. Poly(lactic acid) microspheres released 70-85% of total 5-FU over 7 days. Microspheres of polymers with a smaller molecular weight released the drug more rapidly. Copolymer microspheres released 98% of 5-FU over 2 days. The rate of drug release was controllable by changing the molecular weight of the polymers or using a matrix of copolymer. The intravitreal kinetics of the microspheres were studied in ten rabbits in vivo. A suspension of microspheres was injected into the vitreous cavity of five normal eyes and five vitrectomized eyes. By 48 +/- 5.2 days after injection, the microspheres disappeared from the vitreous cavity in the five normal eyes. Clearance from the vitreous cavity was accelerated in the five rabbits that underwent vitrectomy (14 +/- 2.4 days; P less than 0.001). No difference was found in the b waves of electroretinograms before and after injection of the microspheres. The histologic study showed no abnormal findings as a result of the injection. These results suggested that microspheres of biodegradable polymers may be a potential delivery system for the controlled release of drugs in the vitreous.
Animals↗
Evaluation of blood flow measurements with microspheres and rubidium--an experimental study in rats.
The microsphere method has been widely used for blood flow measurements in normal and tumour tissues. The microsphere method was evaluated for repeated measurements of cardiac output and regional blood flow in anesthetised rats and in anesthetised rats given noradrenalin and thereby having altered haemodynamics with special emphasis on liver blood flow. Comparing the microsphere method with the soluble indicator method (86Rubidium) gave equal cardiac output values. The liver blood flow was lower and the spleen blood flow was higher with the microsphere method. Two microsphere injections at 10 min intervals were performed on anesthetised rats. In one group 817 +/- 10(3) microspheres were injected each time, in a second group 436 +/- 10(3) and in a third noradrenalin was added and then 430 +/- 10(3) microspheres injected twice. There was good reproducibility for cardiac output and for most organ and tissue blood flows between first and second microsphere injection. No influence on arterial liver blood flow was seen. A blood pressure fall and a decreased heart rate was registered after the first injection in the group given 817 x 10(3) spheres. There was also a blood pressure fall in the group given noradrenalin after the first microsphere injection. The microsphere method with two injections of 436 x 10(3) microspheres seems adequate to use in arterial blood flow studies of the liver and simultaneous cardiac output measurements.
Animals↗
Glomerular filtration rate and microsphere distributions in single nephron of rat kidney.
In control non diuretic (ND) and in salt-loaded (SL) rats, both the microsphere technique and the 14C ferrocyanide infusion technique were used to determine the distribution of microspheres in single glomeruli and the SNGFR of the corresponding nephrons. A sample of microspheres with a diameter averaging 11.0 +/- 2.6 mu SD was selected from a 15 +/- 5 mu unlabelled batch. In each rat, three million of these microspheres were injected through the left carotid artery. The microspheres were directly counted under microscopic observation in the glomeruli of the nephrons which were microdissected to determine the SNGFR value. The number of microspheres per glomerulus for a given kidney generally varied from 0 to 8 and was independent to the SNGFR value. The diameter of the microspheres trapped was constant in all the animals. The mean number of microspheres for superificial (S) and juxtamedullary (JM) nephrons was, (ND); S = 1.99 +/- 0.48 SE., n = 5; JM = 3.02 +/- 0.51 SE, n = 5; P less than 0.02, (SL): S = 3.75 +/- 0.53 SE, n = 6; JM = 2.86 +/- 0.33 SE, n = 6; P less than 0.05. This distribution was directly related to that of SNGFR in ND rats (S = 39.0 +/- 6.1 SD and JM = 49.5 +/- 10.3 nl/min) but not in SL rats (S = 50.9 +/- 6.1 and JM = 66.9 +/- 10.0 nl/min). In conclusion, the microsphere technique described in the present paper, appears more suitable for investigating single glomerular blood flow since the number and the size of the microspheres trapped are directly determined at the level of the glomerulus.
Animals↗
Adsorption of fluorescein dyes on albumin microspheres.
The surface characteristics of bovine and egg albumin microspheres were examined using four anionic dyes; sodium fluorescein, eosin, erythrosin, rose bengal, and the cationic dye rhodamine B. The adsorption isotherms of the dyes on unloaded albumin microspheres exhibited Langmuir behavior for dilute solutions of rose bengal, erythrosin, and eosin, suggesting monolayer formation in the initial stages of the sorption process. The adsorption capacity of the microspheres for the dyes (k2) and the affinity constants of the dyes for the microspheres (k1) were found to depend on both the polarizability and the hydrophobic properties of the dye, presumably reflecting the heterogeneous character of the microsphere surface. Further, the extent of sorption at higher dye concentrations was found to depend on the ability of the dye to form stable aggregates inside the microspheres and on environmental long-range forces acting at these sites. At both low and high dye concentrations, the amount adsorbed to the microsphere surface increased with increasing hydrophobicity of the dyes. The lowest adsorption was observed for the nonsubstituted dye fluorescein, whereas the most hydrophobic dye used, rose bengal, was completely adsorbed onto the microsphere surface. The data suggest that the bovine albumin microsphere surfaces are highly hydrophobic and less porous than egg albumin microsphere surfaces.
Adsorption↗
Microscopic analysis of arterial microsphere distribution in rabbit liver and hepatic VX2 tumor.
Microspheres conjugated to radioisotopes and chemotherapeutic agents are playing an important investigative and clinical role in the management of metastatic neoplasms. The purpose of our investigation was to histologically assess the basis for regional intra-arterial microsphere therapy, by comparing the spatial distribution of microspheres in the tumor and liver of experimental models of hepatic metastases. Three New Zealand white rabbits with hepatic VX2 tumor implants were arterially injected with hepatic doses of either 15 or 30 million blue-dyed, polystyrene microspheres (27 microns-diameter). Microscopic examination of random liver and tumor samples revealed that 6-12 times as many microspheres were embolized within tumor than in normal liver (p less than 0.002). The majority of microspheres aggregated into clusters of various size within liver and tumor vasculature, though analysis of cluster sizes illustrated an exponentially skewed distribution toward isolated microspheres. Approximately eight times as many clusters were observed in tumor than in liver (p less than 0.008). Finally, a morphometric analysis was used to quantitate the minimal distances separating microsphere clusters, the intercluster distance (ICD). Analysis of over three thousand intercluster measurements revealed a median ICD approximately five times lower in tumor than in liver (p less than 1 x 10(-8)). This microquantitative analysis provides a fundamental description of how regional intra-arterial microsphere therapy allows the targeted delivery of microspheres to neoplastic tissue, to potentially improve the therapeutic index in the treatment of hepatic metastases.
Animals↗
An experimental model of chronic renal disease in dogs by infusion of microspheres into the renal arterial circulation.
The feasibility of renal arterial infusion of nonbiodegradable microspheres as a model of chronic renal disease in dogs was evaluated. Resin-coated, styrene-divinyl benzene copolymer microspheres were infused into the kidneys of healthy adult Beagles by direct injections of both renal arteries in a single surgical procedure. Injections of 25-microns diameter microspheres had minimal effect on either the clinical status or serum values of the dogs. Histologic examination revealed the majority of the microspheres lodged within the capillary beds of the glomeruli, and little change to the kidneys. However, injections of 50-microns diameter microspheres caused significant increases in serum concentrations of urea nitrogen and creatinine. Histologically, the larger microspheres obstructed afferent arterioles and small arteries, which caused diffuse glomerular necrosis and nephron damage. With doses ranging from 1 to 3 million microspheres/dog, a correlation between the quantity of microspheres injected and severity of renal damage was observed. The optimal dose for producing a model of moderate renal disease was determined to be 1.8 million microspheres/dog (0.9 million microspheres/kidney). During long-term studies, microsphere-injected dogs fed a moderately restricted protein ration remained relatively azotemic, compared with control dogs on the identical ration. During the 5-month postsurgical period, the serum urea nitrogen concentration averaged 18.41 +/- 1.59 mg/dl (mean +/- SE) for the microsphere-injected dogs vs 9.31 +/- 0.38 for the control dogs (P less than 0.001). Similarly, the mean serum creatinine value was significantly higher (P = 0.020) for the microsphere-injected dogs, compared with the controls (1.23 +/- 0.12 mg/dl vs 0.94 +/- 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Dose-dependent variations in blood flow evaluation of canine nerve, nerve graft, tendon, and ligament tissue by the radiolabeled-microsphere technique.
This study evaluates the dose-dependent accuracy of the radionuclide-labeled microsphere technique for blood flow evaluation in nerve, tendon, and ligament. In eight dogs, blood flows were determined for nerve, nerve graft, tendon, and ligament tissue by simultaneous injection of high- and low-dose microspheres with different radiolabels. The results demonstrated no significant differences in blood flow as measured from the small number of microspheres (less than 400) and the high number (more than 400) for nerve and tendon tissue. For nerve tissue, microsphere counts of 50 to 100, 100 to 200, 200 to 300, and more than 300 produced mean percentage errors of 12.74% (n = 5, SEM = 4.52), 5.45% (n = 13, SEM = 1.22), 10.22% (n = 6, SEM = 4.37), and 17.08% (n = 12, SEM = 3.30), respectively. For tendon tissue, the same microsphere subdivisions had mean percentage errors of 7.47% (n = 4, SEM = 2.66), 3.63% (n = 6, SEM = 1.34), 15.54% (n = 4, SEM = 4.43), and 12.91% (n = 1), respectively. For ligament tissue, percentage errors were consistently higher; microsphere counts of 30 to 100, 100 to 200, and 200 to 300 produced mean errors of 20.14% (n = 4, SEM = 6.38), 18.66% (n = 4, SEM = 6.24), and 25.78% (n = 2, SEM = 1.97), respectively. Although there was no direct relationship between percentage error and number of microspheres retrieved, we suggest that microsphere counts in the range of 100 to 200 should be considered acceptable for nerve and tendon in the canine. Ligament tissue seems to be less well suited to the microsphere technique; however, further study is warranted.
Animals↗
Synthesis and characterization of magnetically responsive albumin microspheres containing cis-hydroxyproline for scar inhibition.
Magnetically responsive albumin microspheres containing the proline analog, cis-hydroxyproline, were synthesized and their in-vitro physical properties were characterized. These microspheres have an average size of 1.1 +/- 0.3 microns with 94% of the microspheres less than 2.0 microns. They are uniformly spherical and contain 67% albumin, 22% magnetite, and 8% cis-hydroxyproline. The cis-hydroxyproline is releasable during a 72-h period and demonstrates a slow, releasable pool that constitutes approximately 50% of the incorporated drug. cis-Hydroxyproline is neither chemically nor biologically altered during its incorporation into the microsphere. cis-Hydroxyproline release from microspheres results in the in vitro inhibition of collagen secretion, which is indistinguishable from unincorporated cis-hydroxyproline. In a rat-tail animal model these microspheres were selectively targeted using an external magnetic field applied to a 1.5-2.0-cm target site. Fifty to 80% of the infused microspheres were localized to this site, whereas without a magnetic field only 15-20% of the microspheres are localized to this site. cis-Hydroxyproline microspheres resulted in a 16% decrease in collagen content in a scar model when compared with untreated animals (p less than 0.05). With further refinement of this method of drug delivery, clinically useful inhibition of scar formation may result.
Animals↗