Impediments to eye transplantation: ocular viability following optic-nerve transection or enucleation.

Maintenance of ocular viability is one of the major impediments to successful whole-eye transplantation. This review provides a comprehensive understanding of the current literature to help guide future studies in order to overcome this hurdle. A systematic multistage review of published literature was performed. Three specific questions were addressed: (1) Is recovery of visual function following eye transplantation greater in cold-blooded vertebrates when compared with mammals? (2) Is outer retina function following enucleation and reperfusion improved compared with enucleation alone? (3) Following optic-nerve transection, is there a correlation between retinal ganglion cell (RGC) survival and either time after transection or proximity of the transection to the globe? In a majority of the studies performed in the literature, recovery of visual function can occur after whole-eye transplantation in cold-blooded vertebrates. Following enucleation (and reperfusion), outer retinal function is maintained from 4 to 9 h. RGC survival following optic-nerve transection is inversely related to both the time since transection and the proximity of transection to the globe. Lastly, neurotrophins can increase RGC survival following optic-nerve transection. This review of the literature suggests that the use of a donor eye is feasible for whole-eye transplantation.

Nanoparticles in medicine: therapeutic applications and developments.

Nanotechnology is the understanding and control of matter generally in the 1-100 nm dimension range. The application of nanotechnology to medicine, known as nanomedicine, concerns the use of precisely engineered materials at this length scale to develop novel therapeutic and diagnostic modalities. Nanomaterials have unique physicochemical properties, such as ultra small size, large surface area to mass ratio, and high reactivity, which are different from bulk materials of the same composition. These properties can be used to overcome some of the limitations found in traditional therapeutic and diagnostic agents.

Microchip technology in drug delivery.

The realization that the therapeutic efficacy of certain drugs can be affected dramatically by the way in which they are delivered has created immense interest in controlled drug delivery systems. Much previous work in drug delivery focused on achieving sustained drug release rates over time, while a more recent trend is to make devices that allow the release rate to be varied over time. Advances in microfabrication technology have made an entirely new type of drug delivery device possible. Proof-of-principle experiments have shown that silicon microchips have the ability to store and release multiple chemicals on demand. Future integration of active control electronics, such as microprocessors, remote control units, or biosensors, could lead to the development of a 'pharmacy on a chip,' ie 'smart' microchip implants or tablets that release drugs into the body automatically when needed.

Poly(anhydride-co-imides): in vivo biocompatibility in a rat model.

The degradation and tissue compatibility characteristics of a novel class of biodegradable poly(anhydride-co-imide) polymers: poly[trimellitylimidoglycine-co-1,6-bis(carboxyphenoxy)hexan e] (TMA-gly: CPH) (in 10:90; 30:70 and 50: 50 molar ratios) and poly[pyromellitylimidoalanine-co-1,6-bis(carboxyphenoxy)hexa ne] (PMA-ala:CPH) (in 10:90 and 30:70 molar ratios) were investigated and compared with control poly(lactic acid/glycolic acid) (PLAGA in 50:50 molar ratio) matrices, a well-characterized biocompatible polymer, in rat subcutaneous tissues for 60 days. Polymers were compression-molded into circular discs of 14 mm x 1 mm in diameter. On post-operative days 7, 14, 28 and 60, histological tissue samples were removed, prepared by fixation and staining, and analyzed by light microscopy. PLAGA matrices produced mild inflammatory reactions and were completely degraded at the end of 60 days, leaving implant tissues that were similar to surgical wounds without implants. TMA-gly:CPH (10:90 and 30:70) matrices produced mild inflammatory reactions by the end of 60 days, similar to those seen with PLAGA. TMA-gly: CPH (50: 50) produced moderate inflammatory reactions characterized by macrophages and edema. PMA-ala:CPH matrices elicited minimal inflammatory reactions that were characterized by fibrous encapsulation by the end of 60 days. In vivo degradation rates of poly(anhydride-co-imides) were similar to PLAGA. Both PMA-ala:CPH and TMA-gly: CPH matrices maintained their shapes and degraded at a constant rate over the period of two months. These polymers, possessing good mechanical properties and tissue compatibility, may be useful in weight-bearing applications in bone.

Advances in tissue engineering of blood vessels and other tissues.

Tissue engineering is a new and rapidly expanding field, in which techniques are being developed for culturing a variety of tissues both in vitro and in vivo using polymer 'scaffolds' to support tissue growth. Polymer scaffolds used in tissue engineering are generally biodegradable, often involving compounds which are already approved for human implantation. In some cases, these polymers may be chemically modified to exhibit selective cell adhesion properties, which enhance cell attachment and subsequent tissue growth. Many cell types have been successfully cultured on these scaffolds, including smooth muscle cells, endothelial cells, hepatocytes and chondrocytes. Tissue engineering holds the potential for the in vitro development of autologous or allogeneic transplantable vascular conduits. Each year in the USA, there are approximately 1.4 million procedures performed which require arterial prostheses. Most of these procedures are in small calibre (< 6 mm) vessels, for which synthetic graft materials are not generally suitable. While autologous venous or arterial vessels are generally used, not all patients possess adequate conduit for revascularization. Tubular scaffolds have been specially designed for culturing small calibre arteries in vitro. Bovine aortic vascular cells were seeded and cultured on these polymer scaffolds, and grown under conditions of pulsatile pressure and intra-luminal flow. To minimize contamination during the weeks of tissue culture required to produce an arterial prosthesis, a sterile incubator system was developed. Preliminary studies have achieved good cell densities of both smooth muscle cells and endothelial cells on biodegradable polymer scaffolds.

Lateral diffusion of small compounds in human stratum corneum and model lipid bilayer systems.

An image-based technique of fluorescence recovery after photobleaching (video-FRAP) was used to measure the lateral diffusion coefficients of a series of nine fluorescent probes in two model lipid bilayer systems, dimyristoylphosphatidylcholine (DMPC) and DMPC/cholesterol (40 mol%), as well as in human stratum corneum-extracted lipids. The probes were all lipophilic, varied in molecular weight from 223 to 854 Da, and were chosen to characterize the lateral diffusion of small compounds in these bilayer systems. A clear molecular weight dependence of the lateral diffusion coefficients in DMPC bilayers was observed. Values ranged from 6.72 x 10(-8) to 16.2 x 10(-8) cm2/s, with the smaller probes diffusing faster than the larger ones. Measurements in DMPC/cholesterol bilayers, which represent the most thorough characterization of small-solute diffusion in this system, exhibited a similar molecular weight dependence, although the diffusion coefficients were lower, ranging from 1.62 x 10(-8) to 5.60 x 10(-8) cm2/s. Lateral diffusion measurements in stratum corneum-extracted lipids, which represent a novel examination of diffusion in this unique lipid system, also exhibited a molecular weight dependence, with values ranging from 0.306 x 10(-8) to 2.34 x 10(-8) cm2/s. Literature data showed that these strong molecular weight dependencies extend to even smaller compounds than those examined in this study. A two-parameter empirical expression is presented that describes the lateral diffusion coefficient in terms of the solute's molecular weight and captures the size dependence over the range examined. This study illustrates the degree to which small-molecule lateral diffusion in stratum corneum-extracted lipids can be represented by diffusion in DMPC and DMPC/cholesterol bilayer systems, and may lead to a better understanding of small-solute transport across human stratum corneum.

The ingrowth of new bone tissue and initial mechanical properties of a degrading polymeric composite scaffold.

Trabecular bone deficiency causes a dilemma at surgery in a variety of clinical situations, including trauma, tumor resection, and reconstruction. A synthetic material to replace trabecular bone would be biocompatible, provide temporary mechanical strength to the reconstructed region, and serve as a scaffold upon which new bone could grow (i.e., osteoconduction). In addition, it should serve as a carrier for osteoinductive biomolecules, degrade into nontoxic materials that the body can excrete via normal metabolic pathways, and allow the new bone to remodel along lines of local stress. A particulate filled composite based on an unsaturated linear polyester was designed as a candidate material for this application. The components are mixed with a monomer that cross links the double bonds of the unsaturated polyester. Degradation occurs via hydrolytic degradation of the backbone polymer's ester linkages. This strategy of prepolymer synthesis via condensation polymerization in the laboratory followed by cross linking the unsaturated prepolymer via radical polymerization at surgery offers design flexibility. The radical polymerization allows curing during surgery to facilitate reconstruction of various shaped defects. The laboratory synthesis of the prepolymer allows alterations of its composition and physical properties to effect desired properties in the resulting composite. This study investigates the effect of several composite material formulations on the in vitro mechanical properties and the associated in vivo histologic characteristics of the resulting material. The prepolymer molecular weight, presence of a leachable salt, and amount of cross linking monomer had strong effects on the resulting strength and modulus of the composite. These strengths were on the order of 5 MPa, a magnitude appropriate for consideration of the material as a temporary trabecular bone substitute. The in vivo studies in a rat proximal tibia model demonstrated progressive growth of new bone against the receding surface of the degrading material, and ingrowth of new bone trabeculae into the interior of the degrading specimen. The specimen was also well integrated with the surrounding bone, with no internal fibrosis. There was an absence of a foreign body inflammatory response to the presence of this material over a 5-week time span. This material may thus be an attractive candidate for temporary replacement of trabecular bone, facilitating both osteoconduction and osteoinduction.

Intracerebral drug delivery in rats with lesion-induced memory deficits.

Pharmacological treatments directed at increasing cortical acetylcholine activity in patients with Alzheimer's disease have largely been disappointing, perhaps because denervated areas of brain may not be exposed to adequate amounts of drug. A new method has been developed to enable localized intracerebral delivery of neurotransmitter substances using a polymeric drug delivery system. Microspheres of a polyanhydride sebacic acid copolymer were impregnated with bethanechol, an acetylcholinesterase-resistant cholinomimetic. Twenty rats received bilateral fimbria-fornix lesions, producing cholinergic denervation of the hippocampus and marked impairment in spatial memory. The animals were trained for 2 weeks to run after which they received bilateral intrahippocampal implants of saline (five rats), blank polymer (five rats), or bethanechol-impregnated polymer (10 rats). Following implantation, spatial memory was assessed by radial-maze performance testing for 40 days. Untreated lesioned rats showed persistently poor spatial memory, entering maze arms with near random frequency. Similarly, animals treated with saline and blank polymer did not improve after implantation. Rats treated with bethanechol-impregnated microspheres, however displayed significant improvement within 10 days after implantation; this improvement persisted for the duration of the experiment (p less than 0.05, Student's t-test). Histological analysis of regional acetylcholinesterase staining showed widespread loss of activity throughout the hippocampus bilaterally in all animals. The microsphere implants were visible within the hippocampus, with minimal reactive changes in surrounding brain. It is concluded that intracerebral polymeric drug delivery successfully reversed lesion-induced memory deficits, and has potential as a neurosurgical treatment method for Alzheimer's disease and other neurodegenerative disorders.

Focal arteriolar insudation. A response of arterioles to chronic nonspecific irritation.

The subcutaneous insertion of sterile, inert plastic pellets over the cremaster muscles of rats induces characteristic focal lesions of the arterioles at a distance from the pellets. These lesions appear with a delay of about 6 hours; by light microscopy they are characterized by a focal dilatation accompanied by endothelial damage and increased permeability. They are more severe if the pellets are loaded with histamine and are inhibited if the pellets are loaded with serotonin. Electron microscopy shows interendothelial gaps; the media is massively infiltrated with blood components and fibrin. The medial smooth muscle cells are stretched and at times necrotic; inflammatory cells are scarce. On the basis of these features the lesion was named focal arteriolar insudation (FAI). Although its pathogenesis is not yet clear, the data at hand suggest that it is caused by endogenous mediators affecting the smooth muscle cells and/or the endothelium. FAI appears to be a specific arteriolar response to chronic nonspecific irritation.

Sulfur regulation of heparinase and sulfatases in Flavobacterium heparinum.

Sulfur regulation of heparinase synthesis and sulfatase synthesis was studied in Flavobacterium heparinum. Heparinase synthesis was strongly repressed by sulfate and L-cysteine, while the activity of this enzyme showed little or no inhibition by these compounds. Heparinase was synthesized in the absence of heparin when L-methionine was used as the sole sulfur source. The sulfatases produced by F. heparinum, which include the sulfatases involved in heparin catabolism, were also studied. At least some of the sulfatase activity was regulated by sulfur compounds in a manner similar to heparinase regulation. L-Cysteic acid and taurine were not suitable sulfur sources to support the growth of F. heparinum.

Ethylene-vinyl acetate copolymer microspheres for controlled release of macromolecules.

A simple technique has been devised for preparing ethylene-vinyl acetate copolymer microspheres containing macromolecular drugs. Beads with good sphericity were formed by a simple extrusion process that can easily be repeated by any laboratory without special equipment. The extruded droplets gelled on immediate contact with cold ethanol in a dry ice-ethanol bath. The ethanol also served to remove the solvent and harden the microspheres as they warmed to room temperature. Release of bovine serum albumin followed the expected trends, i.e., initial linearity with the square root of time and faster release rates with greater drug loading.

Heparinase: in vivo activity and immunogenicity in rabbits.

Anticoagulation with heparin is required during extracorporeal circulation for hemodialysis and cardiopulmonary bypass as well as during vascular surgery. Reversal of anticoagulation with protamine may be associated with hypotension and rebound anticoagulation and requires stoichiometric doses. Heparinase from Flavobacterium heparinum catalytically degrades heparin and reverses its anticoagulant effect. Heparin was administered to New Zealand White rabbits and plasma levels were assayed with the APTT anticoagulant assay and the azure A chemical assay. Heparinase actively degraded heparin both in vitro in rabbit plasma and in vivo in rabbit blood as determined by both the anticoagulant and chemical assays when compared to control heparin disappearance curves. Antibodies to heparinase were demonstrated by the ELISA technique in rabbits receiving i.v. heparinase. These antibodies, however, did not effect the activity of the enzyme in vitro or in vivo. No toxic effects of heparinase were noted in observations of the animals or in blood and histologic studies. Heparinase, either free or immobilized, may be a useful heparin-reversing agent without the drawbacks of protamine.

A new method for the three-dimensional in vitro growth of human cancer cells.

A method has been developed which allows, for the first time, the in vitro growth of human tumor cells in calcium alginate gel microcapsules. The three-dimensional matrix is permeable to macromolecules of at least 200 000 molecular weight (MW) (e.g., carcinoembryonic antigen) and provides an environment for organized growth and differentiation more comparable to in vivo growth than monolayer culture. This inexpensive, nondestructive procedure allows studies of morphological, biochemical and immunochemical parameters of human tumor cells within a single model.

Perivascular meningeal projections from cat trigeminal ganglia: possible pathway for vascular headaches in man.

Peroxidase-containing cell bodies were found in the ipsilateral trigeminal ganglia after horseradish peroxidase was applied to the proximal segment of the middle cerebral artery in seven cats. Cell bodies containing the enzyme marker were located among clusters of cells that project via the first division. The existence of sensory pathways surrounding large cerebral arteries provides an important neuroanatomical explanation for the hemicranial distribution of headaches associated with certain strokes and migraine.