Air-filled Albumin Microspheres Research Articles

Gadolinium Oxide Nanoparticles as Potential Multimodal Imaging and Therapeutic Agents

Potentials of hydrophilic and biocompatible ligand coated gadolinium oxide nanoparticles as multimodal imaging agents, drug carriers, and therapeutic agents are reviewed. First of all, they can be used as advanced T1 magnetic resonance imaging (MRI) contrast agents because they have r1 larger than those of Gd(III)-chelates due to a high density of Gd(III) per nanoparticle. They can be further functionalized by conjugating other imaging agents such as fluorescent imaging (FI), X-ray computed tomography (CT), positron emission tomography (PET), and single photon emission tomography (SPECT) agents. They can be also useful for drug carriers through morphology modifications. They themselves are also potential CT and ultrasound imaging (USI) contrast and thermal neutron capture therapeutic (NCT) agents, which are superior to commercial iodine compounds, air-filled albumin microspheres, and boron ((10)B) compounds, respectively. They, when conjugated with targeting agents such as antibodies and peptides, will provide enhanced images and be also very useful for diagnosis and therapy of diseases (so called theragnosis).

Changes of protein solutions during storage: a study of albumin pharmaceutical preparations

During the production of air-filled albumin microspheres, to be used as an ultrasound contrast agent, it was observed that some albumin lots could not be used owing to albumin precipitation. In order to understand the reason for these lot-to-lot variations, 24 lots of 5% (w/v) human albumin pharmaceutical preparations were analysed. The results revealed that the good albumin lots all contained <0.03 mol of free SH groups per mol of albumin. The precipitation observed with other lots was most probably due to higher amounts of free SH groups. The lower amount of free SH groups in the good lots correlated with: (i) a yellow colour of the solutions and a UV-visible spectrum similar to that observed for non-enzymatic glycosylation; (ii) a decreased fructosamine content; (iii) an increased mobility against the anode in isoelectric focusing; and (iv) an increased truncation of the two N-terminal amino acids. No, or only small, differences were observed for the amounts of albumin dimer, albumin aggregates and protein impurities, and these could not account for the albumin precipitation. The differences observed between the albumin lots were most probably due to varying storage times and/or storage conditions, and incubation experiments revealed changes in all parameters that differed between the good and bad lots. Increasing the storage temperature or exposing the solutions to light resulted in a faster decrease of free SH groups and increase of the yellow colouration. It is likely that at least some of the changes observed were due to reactive degradation products formed from the stabilizer N-acetyl-L-tryptophan. The results presented should also be of interest regarding the storage of monoclonal antibodies and other proteins used in pharmaceuticals.

Effect of microsphere size distribution on the ultrasonographic contrast efficacy of air-filled albumin microspheres in the left ventricle of dog hearts.

The in vitro ultrasonographic contrast efficacy of air-filled albumin microspheres has been found to depend on the size distribution of microspheres. The objective of the current study was to empirically describe the relationship between the size distribution of injected air-filled albumin microspheres and the in vivo contrast efficacy after lung capillary filtration in a dog model. Twenty different air-filled microspheres with large and well-defined differences in size distribution were prepared from nine different batches of Albunex (Molecular Biosystems Inc.) and subsequently characterized by Coulter counting. The in vivo ultrasonographic contrast enhancement of these preparations was investigated with a VingMed CFM750 in closed chest model in six mongrel dogs. The observed contrast efficacy, measured as gray-level enhancement in the left ventricle (LV), was correlated to the microsphere size distribution, using both univariate and multivariate approaches. The results demonstrated a significant contribution to LV contrast efficacy from microspheres larger than approximately 7 microm, and a lack of contribution from microspheres smaller than approximately 7 microm. Linear relationships were found between LV contrast efficacy, and both the number concentration of microspheres between 8 to 12 microm and the total microsphere volume concentration. No significant covariance between in vivo contrast efficacy and the number concentration between 1 to 38 microm or 4 to 10 microm was observed. The multivariate model showed a significant contribution to the in vivo gray-level enhancement from microspheres in the size range 7 to 15 microm, with optimal efficacy per microsphere at approximately 13 microm. Large microspheres (> 7 microm), which had been expected to be trapped in the lung capillary bed, contribute most of the observed ultrasound contrast in the LV of the heart.

Detection of aortic insufficiency during ultrasound contrast imaging: Pressure sensitive characteristics of albunex® produce negative contrast angiogram

Detection of aortic insufficiency during ultrasound contrast imaging: Pressure sensitive characteristics of albunex® produce negative contrast angiogram

Precision and accuracy of analysis of air-filled albumin microspheres using Coulter Multisizer Mark II.

The suitability of the electrical sensing zone technique for routine analysis of air-filled albumin microspheres has been thoroughly investigated using three Coulter Multisizer Mark II instruments. The precision of the method, expressed as repeatability relative standard deviation (RSD), was found to be 1-2% for number distribution parameters and 3-4% for volume distribution parameters. Significant instrument-to-instrument variation as high as 11% was, however, also observed. Accuracy was evaluated from analyses of commercially available latex standards and from comparison of results from Coulter analysis with results from the following alternative techniques: light diffraction, optical microscopy and gravimetry. Accuracy, expressed as the difference from either certified values or values obtained with the alternative techniques, was found to be 100-106%.

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.

Biodistributions of air-filled albumin microspheres in rats and pigs.

The air-filled microspheres of the ultrasound-contrast agent Albunex are unique in that the walls consist of human serum albumin molecules which have been made insoluble by sonication of the albumin solution. The microspheres were isolated by flotation, and the washed microspheres were labelled with 125I. The labelled material was cleared from the circulation mainly as particles, not as soluble albumin molecules. In rats, 80% of intravenously injected microspheres were cleared from the blood within 2 min. Nearly 60% of the dose was recovered in the liver, only 5% in the lungs, 9% in the spleen, and negligible quantities in kidneys, heart and brain. Of the radioactivity in the liver, more than 90% was taken up by Kupffer cells (liver macrophages). The protein in the liver was degraded apparently with first-order kinetics (half-life 40 min). In pigs, over 90% of the intravenously injected dose was recovered in the lungs. The vastly increased recovery in pig lungs, compared with that in rats, is probably due to the pulmonary intravascular macrophages of the pig; macrophages are not normally found in this location in rats (or humans). In a separate series of experiments in rats, the biodistribution of shell material from the microspheres was examined. The microspheres were made to collapse by applying external pressure on the suspension, leaving sedimentable protein material consisting of layers of insoluble albumin from the 'shells' surrounding the air bubble. The 'shells' and the microspheres were cleared from the circulation and taken up by the liver with the same kinetics. In the lungs, a higher proportion (15%) of shells than of microspheres was recovered.

Human albumin base echocontrast agents—repeated use in animals may induce anaphylactic reactions

Our attention was drawn to an abstract in the Proceedings of the BMUS meeting in the British Journal of Radiology by J S Boyd at the Department of Veterinary Anatomy, University of Glasgow Veterinary School [1]. It was suggested that recently developed echocontrast agents may be of potential value for use in domestic animals. Albunex™, one of these contrast agents which has been developed by Nycomed Imaging AS in cooperation wityh Molecular Biosystems Inc., San Diego, consists of small air-filled albumin microspheres suspended in human albumin solution (5%).

Intracoronary air-filled albumin microspheres for myocardial blood flow measurement

Objectives. The aim of this study was to explore the possibility of quantifying coronary blood flow by myocardial contrast echocardiography with air-filled serum albumin microspheres (Albunex).Background. Air-filled albumin microspheres have been proposed as an intravascular tracer for the study of myocardial perfusion by contrast echocardiography.Methods. In six anesthetized open chest dogs, the left circumflex coronary artery was cannulated and perfused by a roller pump with blood from the femoral artery. Both air-filled albumin microspheres (0.4 ml, 2 × 108spheres/ml) and technetium-99m-labeled albumin were injected as a bolus into the coronary cannula at baseline and after treatment with dipyridamole (0.56 mg/kg body weight intravenously for 4 min). Two-dimensional echographic images of the left ventricular short axis were digitized to generate myocardial time-intensity curves; myocardial radioactivity was measured by an external detector to generate radionuclide time-activity curves.Results. After dipyridamole, left circumflex coronary artery blood flow (as measured by both the pump and an electromagnetic flow meter) significantly increased (from 1.06 ± 0.28 to 3.61 ± 1.43 ml/min per g of myocardium). Peak intensity and rise time of contrast echo curves were able to differentiate baseline myocardial perfusion from coronary hyperemia but did not show any significant correlation with coronary blood flow. A weak inverse correlation with coronary blood flow was provided by myocardial mean transit time of air-filled albumin microspheres (r = 0.33). Conversely, a close inverse correlation with coronary blood flow was obtained by myocardial mean transit time of technetium-99m-labeled albumin (r = 0.95). Myocardial transit time of air-filled albumin microspheres (1.95 ± 0.60 s) was also markedly shorter than that of labeled albumin (5.35 ± 3.43 s, p < 0.001) and the measurements were less reproducible.Conclusions. In this experimental study, coronary blood flow was not adequately quantified by myocardial contrast echocardiography with intracoronary injection of air-filled albumin microspheres.

Lysosomal and endosomal heterogeneity in the liver: A comparison of the intracellular pathways of endocytosis in rat liver cells

Air-filled albumin microspheres, asialoorosomucoid and formaldehyde-treated serum albumin are selectively taken up by endocytosis in rat liver Kupffer cells, parenchymal cells and endothelial cells, respectively. Intracellular transport and degradation of endocytosed material were studied by subcellular fractionation in sucrose and Nycodenz gradients after intravenous injection of the ligand. By using ligands labeled with 125I-tyramine-cellobiose, the subcellular distribution of labeled degradation products can be studied because they are trapped at the site of formation. The results show that the kinetics of intracellular transport are different in hepatic parenchymal, endothelial and Kupffer cells. In endothelial cells, the ligand is associated with two types of endosomes during the first minutes after internalization and then is transferred rapidly to the lysosomes. In parenchymal cells, 125I-tyramine-cellobiose-asialoorosomucoid was located in a relatively slowly sedimenting vesicle during the first minute after internalization and subsequently in denser endosomes. Degradation of 125I-tyramine-cellobiose-asialoorosomucoid in parenchymal cells started later than that of 125I-tyramine-cellobiose-formaldehyde-treated serum albumin in endothelial cells. Furthermore, the ligand seemed to be transferred relatively slowly from endosomes to lysosomes, and most of the undegraded ligand was in the endosomes. The rate-limiting step of proteolysis in parenchymal cells is probably the transport from endosomes to lysosomes. In Kupffer cells, most 125I-tyramine-cellobiose-microspheres are found as undegraded material in very dense endosomes up to 3 hr after injection. After 20 hr, most of the ligand is degraded in lysosomes distributed at a lower density than the endosomes in Nycodenz and sucrose gradients.

Albunex: A Safe and Effective Commercially Produced Agent for Myocardial Contrast Echocardiography

Microbubble solutions of sonicated human serum albumin have been shown to be effective echocardiographic contrast agents free from adverse effects on coronary blood flow, left ventricular function, and systemic hemodynamics. Albunex is a commercially prepared solution of air-filled albumin microspheres prepared from sonicated 5% human serum albumin. The effects of Albunex on coronary blood flow, left ventricular function, and systemic hemodynamics, as well as contrast enhancement were evaluated in 10 open chest, anesthetized dogs. After an intracoronary injection, Albunex did not alter left atrial, left ventricular systolic or end-diastolic, or mean aortic pressures. It did not cause a coronary hyperemic response, alter left ventricular systolic thickening, or lower the peak positive left ventricular dp/dt. It did not alter these measurements even in the presence of a critical coronary stenosis. The contrast opacification produced by Albunex microbubbles was dose dependent (optimal dose range of 0.033 to 0.5 ml/kg), with attenuation occurring at higher doses. In conclusion, although Albunex provides adequate contrast enhancement, intracoronary injection of Albunex does not significantly alter coronary blood flow, left ventricular function, or systemic hemodynamics. Because of the standardized size and concentration of the microspheres, Albunex may be an ideal agent for myocardial contrast echocardiography.