Cross-linked Albumin Research Articles

Development of specific organ targeting drug delivery system II: Physico-pharmaceutical study on the cross-linked albumin microspheres containing cytarabine

Bovine serum albumin microspheres containing cytarabine were prepared using cross-linking agent, formaldehyde. The shape and the size distribution of them were observed. The shape of them was spherical and the surface was compact and smooth. The size distribution of them was affected by dispersion forces during emulsification. The release of cytarabine from albumin microspheres was dependent upon cross-linking time, amount of cross-linking agent and drug/albumin ratio. However, the difference of drug release by the dispersion forces was not great. After release test, the shape of albumin microspheres was non-spherical and the albumin matrix seemed to be a little relaxed. The degradation tests of albumin microspheres by the proteolytic enzyme showed that albumin microspheres were progressively digested according to the cross-linking degree.

Enhanced tumor metastases upon drug delivery in cross-linked albumin beads.

Growth of the murine hepatoma H6 was significantly suppressed by amiloride, a sodium influx inhibitor. Primary tumor growth inhibition was augmented by loading the drug into cross-linked albumin carriers, but lung metastases were enhanced. These results emphasize the importance of using metastatic tumor models when testing new drugs and/or alternative modes of drug delivery.

In vitro release of adriamycin from drug-loaded albumin and haemoglobin microspheres.

Release of adriamycin from albumin and haemoglobin microspheres has been determined in vitro using a flow through system. Release from cross-linked albumin microspheres is controlled by the percentage of glutaraldehyde used but release profiles of spheres of 23, 41 and 60 microns diameter were virtually superimposable. Not all of the adriamycin is released from the microspheres over 20 h; as biodegradation occurs in vivo after 24 h the amount of drug remaining in the system at 20 h is likely to be principally released by degradation of the protein matrix in vivo. Estimates of the retained adriamycin vary from 16-26 per cent for albumin (n = 3) and 30 per cent for haemoglobin (n = 1).

Cytocompatibility of albuminated polyester fabrics.

An alternative to the usual technique of preclotting porous textile vascular prostheses prior to surgical implantation is to render them impermeable to blood by impregnation with a cross-linked albumin filler matrix. This material subsequently becomes the foundation for cellular development. The compatibility of such impregnated fabrics with newly formed endothelial cells has been evaluated by an in vitro organotypic culture method. This technique enables the characterization and numeration of cells that develop on blood contact surfaces and enables determination of their rate of development. Woven, knitted, and velour fabrics were evaluated following coating with albumin and either storage in Tyrode solution or 40% ethanol or desiccation by critical point drying. Preclotted cardiovascular repair fabrics prepared according to conventional surgical protocol served as controls. The identification of the newly formed cells was confirmed histologically. The most extensive and rapid cellular development was observed on the woven fabric and is believed may have resulted from the smoother surface topography of this substrate. Good cellular development was noted particularly on fabrics which had been stored in Tyrode solution. Ethanol had a deleterious effect on the apparent compatibility.

Albumin Coating of a Knitted Polyester Arterial Prosthesis: An Alternative to Preclotting

Coating a knitted polyester arterial prosthesis with cross-linked albumin fills the interstices of the graft and relieves the surgeon of the necessity to preclot. This is of particular value in patients whose blood clotting properties are hypercoagulable, or hypocoagulable. In addition, such prostheses require less handling, which can lower the risk of bacteremic colonization and shorten the operative time. The in vivo behavior of the implanted albuminated prosthesis in the thoracic aorta of dogs is similar to that of preclotted grafts, although the sequences of early healing are different. The preclotted graft develops a continuous, thick thrombotic matrix on its luminal surface during the first 4 hours of implantation. Following the initiation of the fibrinolytic mechanism 24 to 48 hours postoperatively, this thrombotic deposit quickly recedes, leaving blood cells and platelets adhering here and there to the prosthetic surface. In comparison, the albuminated coating is not associated with major early thrombotic deposits. The albumin remains visible between the filaments during the first 2 weeks of implantation. Both treated and control grafts contain numerous thrombi on their inner surface after 1 to 2 weeks. After 1, 3, and 6 months, both implants are well encapsulated and present a glistening and continuous luminal surface. This excellent healing, however, can be compromised should the graft adhere too closely to the animal's lungs. After 6 months, the cleaned, explanted prosthesis shows a well-preserved textile structure. Because of the reduced risks of postoperative hemorrhage and acute thrombosis and the ease of preparation, handling, and suturing, we believe an albumin coating provides a desirable and viable alternative to preclotting polyester prostheses.

Biodegradable cross-linked albumin microcapsules for embolization.

The interfacial polymerization process used in the present study produced individual cross-linked albumin microcapsules, the particle size of which depended on the emulsification stirring rate. The variation in cross-linking agent concentration altered the microcapsule wall properties. As shown by SEM observations, microcapsules prepared with low acyl chloride concentrations presented rippled surfaces, while the surfaces of the microcapsules prepared with high acyl chloride concentrations were smooth. It was then suggested that the membranes of the weakly cross-linked microcapsules consisted of cross-linked and denatured albumin. Embolization experiments in the dog kidney showed that the weakly cross-linked microcapsules were biodegradable within 7 days, whereas the highly cross-linked microcapsules were degraded over more than 14 days and led to prolonged ischaemia. The results of the histological experiments carried out on a further eight dogs supported the previous findings yielded by the angiographical experiments. Moreover, they indicated that no foreign body reaction occurred. The lack of this inflammatory granuloma should be attributed to the rapid biodegradation of the microcapsules which produced reversible ischaemic lesions.

Fine structure of a periciliary ridge complex of frog retinal rod cells revealed by ultrahigh resolution scanning electron microscopy.

We studied the junctional region between rod inner segments (RIS) and outer segments (ROS) in frog retinas by high resolution scanning electron microscopy (SEM). Retinas of dark adapted or light exposed Rana pipiens were critical-point-dried and RIS and ROS were split and coated with ultrathin metal films of niobium and chromium--or decorated with gold--and imaged in a new SE-I imaging mode. The connecting cilium (CC) usually broke at the base of the RIS and remained attached to the ROS. The outer part of the CC plasmalemma expanded to form liplike protrusions beyond which disks evaginated with successively larger diameter until they reached the full width of the ROS. The CC rose out from an invagination of the RIS apical plasma membrane (PM). On the lateral walls of this invagination, a highly ordered complex of nine symmetrically arrayed ridges and grooves rose steeply and extended laterally approximately 0.4-1 micron on the adjacent RIS PM. On the apical plasmalemma, the ridges and grooves formed groups of three to four parallel rows that surrounded the invagination. The grooves were bridged by filaments anchored at the top edges of the ridges. This highly ordered structure we term the periciliary ridge complex (PRC). Its ninefold symmetry apparently reflects the 9 + 0 microtubule organization of the CC axoneme. The three-dimensional structure revealed by SEM was confirmed by transmission electron microscopy (TEM) of sections of Epon-embedded retinas. TEM-immunocytochemistry on thin sections of retinas embedded in glutaraldehyde cross-linked albumin suggested that the PRC and the CC may participate in opsin transport and disk morphogenesis.

Implanting the glucose enzyme electrode: problems, progress, and alternative solutions.

An implantable glucose sensor is needed before a reliable artificial pancreas can be realized. The principles and current status of one such device, the glucose enzyme electrode, is presented and discussed. While monitoring glucose this enzyme sensor consumes enough oxygen to become oxygen-limited. This problem has been solved by developing hydrophobic membranes that are more permeable to oxygen than to glucose. Two types of membranes with this property made from (1) cross-linked albumin and (2) sebacyl chloride (nylon) are described. Placing these membranes over the glucose enzyme electrode solves the problem of oxygen limitation. Furthermore, the addition of this type of membrane increases the linear response range of the electrode to glucose to include the entire clinical range of interest (0-400 mg/dl). Other problems in developing an implantable glucose sensor are discussed. Competing strategies to achieve an implantable artificial pancreas without using electronic or mechanical components are presented and evaluated.

Resin hemoperfusion for unconjugated bilirubin removal.

The application of an anionic macroreticular ion exchange resin, coated with a thin cross-linked albumin layer, as a hemoperfusion device for the removal of unconjugated bilirubin from the blood of hyperbilirubinemic newborn babies is reviewed. In vivo hemoperfusion runs with hyperbilirubinemic animal models - either by a choledocho-suprarenal vein shunt or by direct infusion of bilirubin into the vein - showed that a 40-ml resin column can remove some 20 mg bilirubin in 3 h. Hemoperfusion of female 8-14 kg baboons showed no significant effect of the column on blood chemistry and coagulation factors and repeated runs had no ill effects.

Bilirubin Removal from an Hepatic Failure Patient by Resin Hemoperfusion

An hemoperfusion (HP) column, packed with beads of a macroreticular MR ion exchange resin which were made biocompatible by coating with a fine layer of cross-linked human albumin, was applied to the removal of bilirubin (BIL) from a jaundiced 69-year old man with hepatic failure. The column was found most suitable for BIL removal. However, the high volumetric mass transfer coefficient of the unconjugated (UC) BIL indicates that this column could best be used for BIL removal from babies suffering from unconjugated hyperbilirubinemia.

Blood compatibility of silicone rubber chemically coated with cross-linked albumin.

A new method is reported for chemically coating cross-linked albumin onto silicone rubber in an attempt to improve the blood compatibility of the material. Promising results were obtained in an evaluation using both vena cava and renal embolus antithrombogenicity tests ondogs. Coated silicone rubber rings induced much less renal emboli than uncoated ones after one week implantation.

Preparation of cross-linked human serum albumin labelled with 125I for studies of reticuloendothelial system function.

A method is described to prepare a new test substance for reticuloendothelial system (RES) function studies. Glutaraldehyde was used for the cross-linking of human serum albumin. The polymeric product was fractionated by repeated chromatography on Sepharose 6B. Cross-linked material with a particle size of approximately 18 nm, as evidenced by electron microscopy, was pooled and labelled with 125I. The surface charge of the albumin polymers, determined by agarose gel electrophoresis, was not significantly changed compared with that of the original albumin monomer. Cross-linking takes place almost entirely between the epsilon-amino groups of lysine in the albumin molecules, as confirmed by amino acid analysis. Preliminary biological tests on mice indicate that the cross-linked polymers are phagocytosed mainly by RE cells of the liver and spleen. The disappearance rate was similar to that of other RE test substances. Intravenous administration of more than 50 times the usual dose caused no deaths, indicating a very low toxicity. Trace amounts of glutaraldehyde were not detectable by gas chromatography. Judging from these experiments, this new preparation of cross-linked albumin fulfils many of the criteria stated for an ideal RES test substance.

Cross-linked albumin as supporting matrix in ultrathin cryo microtomy

A method is described by which tissue blocks and cell cultures can be rapidly encapsulated for cryoultramicrotomy. Bovine serum albumin, insolubilized with glutaraldehyde, has been found to be a good embedding medium for biological purposes. Ultrathin frozen sections with large fields that are sufficiently uniform for low and high magnification micrographs can be readily obtained. The fine structure of cells and at least some of their enzymatic and chemical properties can be preserved by the described procedures.