Subcutaneous Xenotransplantation of Hybrid Artificial Pancreas Encapsulating Pancreatic B Cell Line (MIN6): Functional and Histological Study

The biohybrid artificial pancreas is designed to enclose pancreatic endocrine tissues with a selectively permeable membrane that immunoisolates the graft from the host immune system, allowing those endocrine tissues to survive and control glucose metabolism for an extended period of time. The pancreatic B cell line MIN6 is established from a pancreas B cell tumor occurring in transgenic mice harboring the human insulin promoter gene connected to the SV40 T-antigen hybrid gene. It has been proven that glucose-stimulated insulin secretion in MIN6 cells retains a concentration-dependent response similar to that of normal islets. In this study, we performed the histological and functional examination of three-layer microbeads employing MIN6 cells after subcutaneous xenotransplantation to evaluate this device as bioartificial pancreas. MIN6 cells were microencapsulated in three-layer microbeads formulated with agarose, polystyrene sulfonic acid, polybrene, and carboxymethyl cellulose. Microbeads were xenogenically implanted in the subcutaneous tissue of the back of Lewis rats with streptozotocin-induced diabetes. One week after implantation, microbeads were retrieved and cultured for 24 h before the static incubation. There was no evidence of adhesion to the graft and the fibrosis in the transplantation site as determined by gross visual inspection. Microscopic examination demonstrated that retrieved microbeads maintained normal shape, containing intact MIN6 cells. Histological study showed that these MIN6 cells in the microbeads appeared to be viable without cellular infiltration within or around the microbeads. Immunohistochemical analysis of the microbeads clearly revealed the intense staining of insulin in the cytoplasm of encapsulated MIN6 cells. Insulin productivity of MIN6 cells in the microbeads is strongly suggested to be preserved. In response to 16.7 mM glucose stimulation, static incubation of microbeads 1 wk after implantation caused the 2.3 times increase in insulin secretion seen after 3.3 mM glucose stimulation (84.3 ± 10.0 vs. 37.4 ± 10.7 μU/3 × 106 cells/hr, n = 5 each, p < 0.01). This study demonstrates that three-layer microbeads encapsulating MIN6 cells retain excellent biocompatibility and maintain good insulin secretion even after subcutaneous xenotransplantation, suggesting the possible future clinical application of this unique bioartificial pancreas to subcutaneous xenotransplantation.

Improved Large-Scale Isolation of Breeder Porcine Islets: Possibility of Harvesting from Nonheart-Beating Donor

To establish a large-scale isolation procedure for adult porcine islets usable as a donor source for xenotransplantation and as a model of human islet isolation, we improved several characteristics of the conventional isolation procedure. At a slaughterhouse we first selected a breeder pig over 1.5 years old (and over 200 kg in weight) with warm ischemic time (WIT) of 15 ± 2 minutes as nonheart-beating donors. Then, we made a special enzymic mixture that consisted of collagenase S-1 (260 U/mg, NittaZelatin, Japan), collagenase P (1.86 U/ml Lyo Boehringer-Mannheim, USA), DNase (Sigma, St. Louis, Mo), Disparse (NittaZelatin, Japan), and protease inhibitor (Sigma). Third, this mixture was injected very gently into the pancreatic duct at the time of pancreatic harvesting. To prevent overdigestion of the pancreas, the mixture was first cooled to less than 10°C. Fourth, during the warm digestion of pancreas, the pancreas with the enzymic mixture was quietly put in a water bath at 37°C without mechanical shaking. Fifth, we purified the islets with a COBE 2991 cell processor by the Dextran 70 gradient method, because Dextran 70 is very cheap and has the same purification effect as the Ficoll gradient. The results of 10 consecutive breeder porcine islet isolations are reported. The total yield of isolations of islets over 50 μm in the longest diameter after staining with Dithizone (DTZ) was 85,900 ± 19,954 islets, 291,667 ± 240,452 IEQ (2,900 ± 2,324 IEQ/g). The purity of the isolated islets was very high: 90.2 ± 3.8%. Glucose stimulation during in vitro incubation induced significant insulin release from isolated breeder porcine islets. In two of the diabetic rats receiving encapsulated islets grafts using a mesh-reinforced polyvinyl alcohol hydrogel bag (MRPB), a prominent reduction in serum glucose levels (less than 200 mg/dL) persisted for 13 and 19 days, respectively, after intraperitoneal xenotransplantation islets without immunosuppression. In conclusion, we succeeded in a more efficient and less-expensive isolation of a large amount of adult porcine islets from a nonheart-beating donor.

Gelatin Density Gradient for Isolation of Islets of Langerhans

Isolation of islets of Langerhans (islets) has been performed by means of collagenase digestion of the pancreatic tissue combined with density gradient separation of islets from unwanted exocrine tissues. An enormous number of islets are necessary for clinical islet transplantation. The density gradient used for isolation of a large number of islets should satisfy several requirements in addition to those for the conventional density gradients, such as high viscosity for creating fine interfaces with a large area, easy sterilization, and low cost. This study is concerned with the development of a new density gradient made of low-molecular-weight gelatin. We isolated islets from the hamster pancreatic tissue using the gelatin density gradients. The yield and purity of islet and its insulin release function were compared with those of islets isolated using Ficoll and Ficoll-Conray density gradients that have been conventionally used. The new gelatin density gradient can separate islets from the unwanted exocrine tissue as effectively as the Ficoll density gradient and more effectively than the Ficoll-Conray density gradients. The islets collected using the gelatin gradient retain ability of insulin release increase in response to glucose stimulation, similar to those isolated by the Ficoll-Conray gradient and more than those collected by the Ficoll gradient. In addition, the gelatin effectively inhibited enzyme activities, that is, collagenase and proteolytic enzymes released from the exocrine tissue, and thus it can inhibit overdigestion of islets during their density gradient isolation. The gelatin gradient satisfies most of the additional requirements for islet isolation from the pancreatic tissue of large animals mentioned above. Although several factors, such as molecular weight of gelatin, osmolality of the gradient, and centrifugal conditions, still remain to be optimized, our results suggest that the gelatin gradient has potentiality to isolate islets from the pancreatic tissue of a large animal.

Prolonged Effect of Troglitazone (CS-045) on Xenograft Survival of Hybrid Artificial Pancreas

Troglitazone (CS-045), a thiazolidinedione derivative, is a new oral antidiabetic agent that enhances insulin sensitivity and improves insulin responsiveness. In this study we examined the effects of CS-045 on the survival of xenografted bioartificial pancreas. Isolated rat islets were microencapsulated with three-layer agarose microcapsules (polybrene, carboxymethyl cellulose, and an agarose-polystyrene sulfonic acid mixture). Diabetes was induced by intraperitoneal injection of streptozotocin 220 mg/kg. Recipient diabetic mice were separated into two groups. In the CS-045 treated group, the recipient mice were given feed mixed with CS-045 (0.2% w/w) starting from 1 wk before transplantation up to graft failure. The mice in the control group had feed without CS-045. Three hundred microencapsulated rat islets were xenotransplanted into the intraperitoneal cavity of each recipient mouse in both groups. One month after xenotransplantation, IVGTT was performed for all recipients. Xenotransplantation of 300 rat islets in microcapsules decreased the nonfasting blood glucose levels of both groups within 2 days. In the CS-045-treated group (n = 3), the normoglycemic period lasted for more than 1 mo without administration of immunosuppressive drugs (45 ± 4.3 days). However, in the control group (n = 4), the blood glucose levels of all recipients were already elevated on day 4. In the IVGTT study, the glucose assimilation was markedly and significantly better in the CS-045-treated group than in the control group (K = 1.7 ± 0.1 vs. 0.7 ± 0.28 respectively, p <0.01). This study demonstrates that a newly developed oral antidiabetic agent, CS-045 could favorably ameliorate the diabetic state of the recipients xenotransplanted with the bioartificial pancreas, leading to an improved glucose tolerance and longer xenograft survival.

Phagocytosis of Bioactive Microspheres

The influence of several proteins on the uptake of microspheres was investigated using mouse peritoneal macrophages. Thioglycollate-stimulated macrophages were cultivated for 3 h with protein-grafted and protein-coated cellulose microspheres smaller than 2 μm in the presence and the absence of serum. Bovine serum albumin reduced the phagocytosis of microspheres, while y-globulin, human fibronectin, bovine tuftsin, and gelatin enhanced the phagocytosis. This trend was not influenced substantially by the presence of serum and the mode of surface binding of the proteins; that is, covalent grafting or physical adsorption (coating). However, in the case of gelatin binding, phagocytosis was greatly enhanced by the presence of serum as compared with the other proteins.

Sealing effects of cross-linked gelatin

Surgical sealants form gel when applied to tissues. Currently, fibrin sealant has been successfully used in many surgical fields, but it has several disadvantages, including possible virus transmission, low adhesive strength, and high cost. In this study, gelatin and glutaraldehyde (GA) solutions were chosen to demonstrate the effectiveness of cross-linked gelatin gel as sealant and barrier, both of which have long been used in medical applications. It was found that the gelatin gel prepared from 26 wt% gelatin and 1 wt% GA solutions exhibited bonding strength almost three times higher than that of fibrin glue. The bonding strength increased with the increasing gelatin and GA concentrations. When a needle hole on PTFE vascular grafts was sealed with the gelatin gel, the water-resistant pressure significantly increased upon rubbing and was twice higher than that of fibrin glue. The cytotoxicity of gelatin gel was found to be much lower than that of albumin glue prepared at the same composition as commercially available BioGlue®. The gelatin gel was found to be also effective as barrier to prevent adhesion in a rat cecum abrasion model.

Effect of the structure of bone morphogenetic protein carriers on ectopic bone regeneration

To study the effect of the shape of carriers on bone regeneration, two biodegradable polymeric materials, a polyglycolide (PGA) nonwoven fabric and a gelatin hydrogel, were used as carriers of recombinant human bone morphogenetic protein-2 (rhBMP-2). The PGA nonwoven fabric was made from PGA fibers of 20 microm diameter without using any binders while the gelatin hydrogel was prepared by cross-linking of gelatin in aqueous solution with glutaraldehyde to a water content of 95% when swollen with water. Following impregnation of rhBMP-2, the carriers of disk type were implanted into the Wistar rat thigh muscle. The induction of ectopic bone formation from the rhBMP-2-impregnated carriers was evaluated by Softex and histologic observation after staining the explanted tissue with alizarin red S stain to identify calcium deposition. Both of the biodegradable polymeric carriers containing 10 microg of rhBMP-2 induced ectopic bone formation after 2 weeks of implantation but not at the first week after implantation. A remarkable finding was a difference in the macroscopic morphology between the ectopic bones induced by the PGA nonwoven fabric and the gelatin hydrogel. The PGA nonwoven fabric containing rhBMP-2 induced ectopic bone formation inside of the carrier, whereas the gelatin hydrogel formed bone at the periphery of the carrier.

Cross-linking of gelatin with carbodiimides

Carbodiimides were employed for cross-linking of gelatin through amide bond formation to avoid any foreign bond incorporation into the cross-linked gelatin molecules. Cross-linking of gelatin was performed not in aqueous solution but in the form of a film under a heterogenous condition. Ethanol-water mixtures were used as the reaction medium to prevent dissolution of gelatin films. The optimal ethanol concentration in the ethanol-water mixtures was around 80 vol%, and the water content of the cross-linked gelatin film attained after swelling with water at 25 degrees C was as low as 55 wt%. A water-soluble carbodiimide (l-ethyl-3[3-dimethylaminoprophyl] carbodiimide) was more effective for gelatin cross-linking than a water-insoluble carbodiimide (1,3-dicyclohexyl carbodiimide). The optimal temperature for cross-linking with the water-soluble carbodiimide ranged between 15 and 25 degrees C. It was concluded that gelatin cross-linking with carbodiimides is as effective as that with glutaraldehyde, which is most widely used despite the toxicity, at least, so far as the water content of cross-linked gelatin film is concerned.

Effect of a static magnetic field on ion transport in a cellulose membrane

A cellulose membrane was exposed to the static magnetic field (SMF) in the presence of KCl solution and ion transport through the membrane was measured before and after the SMF exposure. SMF at 0.24 T significantly enhanced the rate of ion transport, especially after the first exposure (p<0.05), while the increased ion transport rate did not return to the initial basal level after exchange of the aqueous medium. These results suggest that an irreversible, temporal conformation change took place on the cellulose membrane or on the water bound to the cellulose surface. The accelerating effect of SMF on the ion transport seems to have occurred as a result of stabilized hydration layer on the cellulose surface.

Usefulness of microspheres composed of gelatin with various cross-linking density

The release rate of insulin, as a model peptide, from gelatin microspheres (GM) prepared with gelatin having various cross-linking densities in vitro was examined. The release of insulin from GM showed the burst effect, followed by a slow release phase regardless of the cross-linking density of gelatin. The total amount of insulin released in 2 weeks decreased with increasing cross-linking density of gelatin. The release rate of insulin within 6 h was well correlated with the cross-linking density of gelatin. The remaining amounts of both insulin and GM after injection of insulin incorporated in GM to mice femoral muscle tissue were also examined in vivo. Both insulin and GM rapidly disappeared from the injection site within 1 day, and thereafter slowly disappeared over 14 days. The time courses of the remaining amounts were fairly similar to each other. Furthermore, the remaining amount of insulin 1 day after administration was well correlated with the cross-linking density of gelatin. These data suggest that insulin was released from GM with the degradation of GM in mice muscular tissue and that the release rate of insulin can be controlled by modifying the cross-linking density of gelatin. In conclusion, the control of the release rate of insulin from GM can be achieved under both in vitro and in vivo conditions by gelatin through the alteration of cross-linking conditions.

Laser-perforated membranous biomaterials induced pore size-dependent bone induction when used as a new BMP carrier

Previously we found that laser perforation of a collagen membrane (35 microm thickness, Koken Co., Tokyo) produced an effective bone morphogenetic protein (BMP) carrier, if the created pore sizes were larger than 0.5 mm. In this study we applied the same technique to create pores of 0.2 and 1.0 mm in a thicker (1.2 mm thickness) porous biodegradable membrane made of polylactic acid and an epsilon-caprolactone copolymer (PLA-CL) to obtain an effective membranous BMP carrier with higher mechanical strength. Pieces of PLA-CL (0.5 x 1.0 x 0.12 cm) combined with rhBMP-2 (5 microg) were implanted subcutaneously into rats and processed for analyses at 1-3 weeks. The laser-perforated PLA-CL membranes equipped with 1.0 mm pores induced mineralization beginning from the margins of the pores judging from the X-ray patterns, but bone formation seemed to proceed irregularly inside the pores. In the perforated PLA-CL membrane with 1.0-mm pores bone formation did not significantly increase compared with the nonperforated one. This was due to the fact that the PLA-CL membrane was already a porous structure (85% porosity). In contrast with laser-perforated PLA-CL 0.2 mm pores, bone was induced on the collagen fibers and fiber bundles inside the pores. The different patterns of bone formation between the PLA-CL membranes with 1.0 and 0.2 mm pores seemed to be related to the active formation of perpendicular collagen fibers through the 0.2 mm pores.

The efficacy of prevascularization by basic FGF for hepatocyte transplantation using polymer devices in rats

This study used polymer devices implanted in rats to investigate the effect of prevascularization by basic fibroblast growth factor (bFGF) on hepatocyte transplantation (HTx). Lewis rats served as both donors and recipients. Polyvinyl alcohol (PVA) sponges with either hydrogel containing bFGF (bFGF group) or distilled water (control group) were implanted between the mesenteric leaves of recipient rats. Hepatotrophic stimulation was induced by a portacaval shunt and a 70% partial hepatectomy. After 1 week of prevascularization, hepatocytes harvested from the donor Lewis rats using a collagenase digestive method were injected into the sponges. Specimens were harvested at 2 weeks, 1 month, and 2 months after HTx. Histologic examination revealed that the control groups contained small numbers of hepatocytes restricted to the peripheral areas of the sponges. However, a large number of hepatocytes, including clusters, was found distributed uniformly in the bFGF group. In the bFGF group at 2 weeks, 1 month, and 2 months, the percentage of the sponge occupied by hepatocytes was 7.21+/-2.64%, 6.98+/-2.59%, and 5.58+/-3.77%, respectively. The corresponding ratios for the control group were 0.40+/-0.39%, 0.40+/-0.40%, and 0.87+/-1.51%. In addition, the mean number of new blood vessels in the bFGF group was significantly greater than that in the control group at 0 days, 2 weeks, and 1 month after HTx. These results suggest that bFGF strongly induced vascularization, which enabled a large number of hepatocytes to survive in the polymer devices.

A trial to prepare biodegradable collagen-hydroxyapatite composites for bone repair

This paper is a trial to prepare collagen-hydroxyapatite composites in vitro by an alternate immersion method. Collagen sponges of different biodegradabilities were prepared through chemical cross-linking of Type I collagen with glutaraldehyde (GA) at concentrations of 0.2, 1.0, and 2.0 wt%. The sponges were immersed at 37 degrees C in Tris-HCl-buffered solution containing 200 mM CaCl2 (pH 7.4) for 2 h and then in an aqueous solution of 120 mM Na2HPO4 (pH 9.3) for a 2 h further (one immersion cycle). The alternate immersion cycle was repeated for different times to obtain collagen-hydroxyapatite composites. The characterization of the resulting composites was performed by Fourier transform infrared spectroscopy (FT-IR). X-ray diffraction (XRD), and scanning electron microscopy (SEM). The weight of composites increased with an increase in immersion cycles and the rate of increase became greater with higher GA cross-linking levels for collagen sponge preparation. The pH of the phosphate solution decreased with the immersion cycle, which suggests H+ generation accompanied hydroxyapatite formation. Irrespective of the GA concentration and immersion cycle, every composite showed IR absorption bands attributable to phosphate and hydroxyl groups at 950-1100 or 550-650 and 3000-3500 cm(-1) and broad peaks specific to hydroxyapatite on the XRD charts. SEM study revealed small white clusters of hydroxyapatite interspersed uniformly on/in the collagen framework without any preferential orientation. The composite prepared from 0.2 wt% GA cross-linked collagen sponge which showed favourable characteristics was applied to a rat skull defect to evaluate its osteoconductivity as well as biodegradability. The formation of new bone tissue was histologically observed at the defect 12 weeks after application in marked contrast to the collagen sponge alone. The composite degraded without any inflammation reaction. It is concluded that the collagen-hydroxyapatite composite prepared by the present method is a biodegradable biomaterial of osteoconductivity applicable to bone repair.

The pH dependence of monofilament sutures on hydrolytic degradation

Hydrolytic degradation of two nonabsorbable sutures, four absorbable sutures, and a new type of absorbable suture was studied in buffered media of various pHs at 37 degrees C. The pH levels fixed in this study were 1.0, 7.4, 8.5, and 10.5. Physical measurements were made on the retention of tensile strength and melting temperature of the sutures after hydrolysis for 12 weeks. Sutures containing glycolic acid as a comonomer exhibited enhanced degradation in alkaline media, similar to polyglycolide multifilament sutures. Poly-p-dioxanone (PDS II) suture lost strength to a significant extent at pH 1.0, suggesting that care should be taken when this suture is used for closing tissues in contact with acidic media, such as the stomach. In marked contrast, the degradation of lactide-epsilon-caprolactone copolymer [P(LA/CL)] suture was not sensitive to the pH of media. The surface morphology of hydrolyzed sutures varied, depending on the pH of media. Particularly, moon-crater-shaped impressions were observed on glycolide-epsilon-caprolactone copolymer (MONOCRYL) and glycolide-trimethylene carbonate-dioxanone copolymer (BIOSYN) sutures. Among the nonabsorbable sutures, nylon (ETHILON) exhibited the fastest loss of strength in acidic buffer solution, and polypropylene (PROLENE) suture retained most of its initial strength at all pHs studied.

Controlled release of growth factors based on biodegradation of gelatin hydrogel

To develop a carrier for the controlled release of biologically-active growth factors, biodegradable hydrogels were prepared through glutaraldehyde cross-linking of gelatin with isoelectric points (IEP) of 5.0 and 9.0, i.e. 'acidic' and 'basic' gelatins, respectively. Radioiodinated growth factors were used to investigate their sorption and desorption from the hydrogel of both types of gelatin. Basic fibroblast growth factor (bFGF) and transforming growth factor-beta1 (TGF-beta1) were well sorbed with time to the acidic gelatin hydrogel, while less sorption was observed for the basic gelatin hydrogel. This could be explained in terms of the electrostatic interaction between the growth factors and the acidic gelatin. However, bone morphogenetic protein-2 (BMP-2) and vascular endothelial growth factor (VEGF), though their IEPs are higher than 7.0, were sorbed to the acidic gelatin hydrogel to a smaller extent than the two other growth factors. Under in vitro non-degradation conditions, approximately 20% of the incorporated bFGF and TGF-beta1 was desorbed from the hydrogels within the initial 40 min, followed by no further substantial desorption, whereas large initial desorption was observed for BMP-2 and VEGF. When implanted in the back subcutis of mice, gelatin hydrogels were degraded over time. Each growth factor was retained in vivo being incorporated in the acidic gelatin hydrogel: the smaller the in vitro desorption amount from the hydrogel, the longer the in vivo retention time. The in vivo profile of bFGF and TGF-beta1 retention was in good accordance with that of the hydrogel. These findings indicate that the growth factor immobilized to the acidic gelatin hydrogel through ionic interaction was released in vivo as a result of hydrogel degradation.

Interaction of poly(2-acrylamido 2-methylpropane sulfonate)-grafted polystyrene beads with cationic complement proteins

Influence of various biomaterials on the complement system in serum has been intensively studied by many research groups, since activation of the complement pathway in vivo has been known to give rise to some pathological conditions, such as inflammation and anaphylaxis. Much effort has been devoted to develop new materials that do not activate or deteriorate the complement system. The present work is aimed at revealing the mode of reactions of anionic poly(2-acrylamido 2-methylpropane sulfonate) grafted on polystyrene bead (PAMPS-g-bead) with serum complement. Complement activity assay, determination of complement proteins levels, and immunoblot analysis were carried out for sera pretreated with PAMPS-g-beads. The results clearly showed that, when PAMPS-g-beads were incubated with serum, those beads adsorbed several complement proteins, i.e. C1q, factor D, factor P, C6, and C8, but the generation of activation fragments of complement components was not observed. Especially, factor D was most effectively removed from serum, resulting in potential inhibition of the alternative pathway. A larger amount of PAMPS-g-beads was needed to decrease the serum CH50 level. That may be caused by removal of C6. Although some polyanions, such as dextran sulfate, were reported to activate the complement system, the obtained results indicate that the PAMPS-g-bead is not an activator of the complement pathway, but acts as an adsorbent of complement components. One possible clinical application of the PAMPS-g-beads is adsorption of serum factor D by extracorporeal treatment of patients with renal failure with a high level of factor D, because the increased quantity of factor D in serum may cause consistent activation of the alternative pathway.

Static magnetic field effects on bone formation of rats with an ischemic bone model

Effects of a static magnetic field were studied on bone formation using an ischemic rat femur model. Metal rods were prepared from magnetized and unmagnetized samariun cobalt to have tapered structure, both with the same geometrical dimension, and were implanted transcortically into the middle diaphysis of 88 rat femurs. Both sides of the rat femoral artery were ligated to create an ischemic bone model, followed by implantation of the tapered rod to the femur. The bone mineral density (BMD) and weight of the femurs were measured at 1st and 3rd week after implantation. The result at the 3rd week post-implantation revealed that the BMD and weight of the ischemic bone model rats were significantly reduced, compared with that of non-operated femur. It was also found that the magnetized group had significantly higher bone weights than the unmagnetized (p<0.05). The BMD of the rats implanted with the magnetized rods were similar to those of the non-operated (p>0.05). This enhancement of the femoral bone formation of the ischemic rat model by the static magnetic field seems to be due to the improved blood circulation of the femur.

Development of an artificial dermis preparation capable of silver sulfadiazine release

This article describes the antibacterial effects of an artificial dermis impregnated with silver sulfadiazine (Ag-SD) in vitro as well as in vivo. In the in vitro test, silver release from the artificial dermis impregnated with Ag-SD, by immersion in collagenase solution was controlled by the degradation of the collagen sponge. The artificial dermis impregnated with 3% or higher doses of Ag-SD completely suppressed the growth of Pseudomonas aeruginosa (Ps.) or Staphylococcus aureus (St.). The cytotoxicity test revealed that impregnation of 5% or higher doses of Ag-SD suppressed the growth of fibroblasts. However, when the artificial dermis impregnated with Ag-SD was implanted into full-thickness skin defects on the backs of guinea pigs, no tissue damage was histologically observed around the implanted site of the dermis. In the in vivo test, the artificial dermis impregnated with 10% Ag-SD, which was grafted on experimentally contaminated wounds in the backs of guinea pigs, macroscopically suppressed degradation of the collagen sponge, and significantly reduced the growth of both Ps. and St., compared with artificial dermis without Ag-SD. We conclude that collagen sponge impregnated with Ag-SD is a promising artificial dermis applicable to treat contaminated wounds.

Derivation of pharmacokinetics equations for quantitative evaluation of bioartificial liver functions

A bioartificial liver (BAL) is an extracorporeal medical device incorporating living hepatocytes in a cartridge. A variety of BALs have been developed and new devices are being introduced. Some of them have been clinically applied and from the results obtained they are claimed to be useful devices for assisting the liver functions of patients. However, there is still uncertainty as to their efficacy and their limitations are not clear. It is important to establish methods to quantitatively evaluate the metabolic and synthetic functions of BAL. In this paper, we derive simple equations for the quantitative evaluation of BAL functions on the basis of pharmacokinetics. Pharmacokinetics was originally developed to understand the processes of absorption, distribution, and elimination of administered drugs. Metabolic functions of the natural liver have been analyzed using pharmacokinetics and values of the useful parameters, clearance (CL) and intrinsic clearance (CLint), have been reported. The metabolic functions of the BAL expressed using values of CL and CLint are easily compared with those of the normal human liver. We believe that our method provides a useful basis for estimating the clinical effectiveness of BAL.

Liver targeting of interferon-beta with a liver-affinity polysaccharide based on metal coordination in mice

Frequent and high-dose i.v. injections of interferon-beta (IFN-beta) have been used clinically to treat patients with viral hepatitis despite various side effects. Because side effects are caused by the systemic effects of IFN-beta, the purpose of this study was to target the drug specifically to the liver, thus reducing the adverse events. A chelating residue, diethylenetriaminepentaacetic acid (DTPA), was introduced to pullulan, a water-soluble polysaccharide with a high affinity for the liver. Murine IFN-beta could be coordinately conjugated with the DTPA-pullulan by simple mixing in an aqueous solution containing zinc ion (Zn2+). Intravenous injection of the IFN-beta-DTPA-pullulan conjugate with Zn2+ coordination enhanced liver induction of an antiviral enzyme, 2',5'-oligoadenylate synthetase (2-5AS), to a greater extent than that by free IFN-beta, although the 2-5AS levels in the liver depended on the mixing ratio of the IFN-beta/DTPA residue of DTPA-pullulan/Zn2+. In addition, the duration of the liver 2-5AS induction by the IFN-beta-DTPA-pullulan conjugate with Zn2+ coordination was longer than that by free IFN-beta. The liver targeting of IFN-beta by DTPA-pullulan with Zn2+ coordination may be a promising IFN therapy.

Tissue-engineered vascular autograft: inferior vena cava replacement in a dog model

Tissue-engineered vascular autografts (TEVAs) were made by seeding 4-6 x 10(6) of mixed cells obtained from femoral veins of mongrel dogs onto tube-shaped biodegradable polymer scaffolds composed of a polyglycolid acid (PGA) nonwoven fabric sheet and a copolymer of L-lactide and caprolactone (n = 4). After 7 days, the inferior vena cavas (IVCs) of the same dogs were replaced with TEVAs. After 3, 4, 5, and 6 months, angiographies were performed, and the dogs were sacrificed. The implanted TEVAs were examined both grossly and immunohistologically. The implanted TEVAs showed no evidence of stenosis or dilatation. No thrombus was found inside the TEVAs, even without any anticoagulation therapy. Remnants of the polymer scaffolds were not observed in all specimens, and the overall gross appearance similar to that of native IVCs. Immunohistological staining revealed the presence of factor VIII positive nucleated cells at the luminal surface of the TEVAs. In addition, lesions were observed where alpha-smooth muscle actin and desmin positive cells existed. Implanted TEVAs contained a sufficient amount of extracellular matrix, and showed neither occlusion nor aneurysmal formation. In addition, endothelial cells were found to line the luminal surface of each TEVA. These results strongly suggest that "ideal" venous grafts with antithrombogenicity can be produced.

Bone formation at a rabbit skull defect by autologous bone marrow cells combined with gelatin microspheres containing TGF-beta1

The objective of the present study is to investigate the addition effect of transforming growth factor (TGF)-beta1 on the bone formation at a rabbit skull defect induced by autologous bone marrow (BM). Following application of gelatin microspheres containing TGF-beta1, with or without BM cells to skull bone defects, bone formation at the defect was assessed by soft X-ray, dual energy X-ray absorptometry (DEXA), and histological examinations. After implantation for 6 weeks, gelatin microspheres containing 0.05 microg of TGF-beta1 plus 10(6) of BM cells induced bone formation at the 6 mm diameter bone defect. The defect was histologically closed by newly formed bone tissue, whilst both gelatin microspheres containing 0.05 microg of TGF-beta1, and 10(6) and 10(7) of BM cells were ineffective. A DEXA experiment revealed that combination of gelatin microspheres containing TGF-beta1 with BM cells enhanced the bone mineral density at the skull defect to a significantly greater extent than other agents. These findings indicate that a combination of gelatin microspheres containing TGF-beta1 enabled BM cells to enhance the osteoinductive ability, resulting in bone formation even at the cell number at which BM cells alone were ineffective.

An oral drug delivery system targeting immune-regulating cells ameliorates mucosal injury in trinitrobenzene sulfonic acid-induced colitis

Control of immune-regulating cells in the colonic mucosa is important in the treatment of patients with inflammatory bowel disease (IBD). The aim of study was to examine the therapeutic effect of dexamethasone (DX) microspheres on 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis in rats, a model for human Crohn's disease. DX microspheres and DX alone were administered orally to rats with TNBS-induced colitis. The macroscopic score, histological score, myeloperoxidase (MPO) activity, nitric oxide (NO) production, and gene expressions of proinflammatory cytokines, cyclooxygenase (COX)-1, and COX-2 in the colonic tissue were determined. Proliferating cell nuclear antigen (PCNA) staining and expression of nuclear transcription factor (NF)-kappaB in colonic tissues were also investigated. Macroscopic score, histological score, MPO activity, and NO production in rats treated with DX microspheres were significantly lower than in those treated with DX alone. The gene expression of proinflammatory cytokines and COX-2 in rats treated with DX microspheres was down-regulated, compared with that in rats treated with DX alone. The number of PCNA-positive cells in the DX microsphere group was larger than in the group treated with DX alone. DX microspheres suppressed NF-kappaB activation in TNBS-induced colitis more strongly than DX alone. Oral administration of DX microspheres appears to ameliorate mucosal injury in TNBS-induced colitis. This drug delivery system could be an ideal therapy for human IBD.

Evaluation of gelatin microspheres for nasal and intramuscular administrations of salmon calcitonin

The suitability of gelatin microspheres for nasal and intramuscular delivery of salmon calcitonin (sCT) was examined. Negatively and positively charged gelatin microspheres were prepared using acidic gelatin [isoelectric point (IEP) value of 5.0] and basic gelatin (IEP=9.0), respectively. The average diameters of positively charged gelatin microspheres in their dried state were 3.4, 11.2, 22.5 and 71.5 microm, while that of negatively charged gelatin microspheres was 10.9 microm. Both types of gelatin microspheres were capable of adhering to the nasal mucosa. The mucoadhesion of positively charged gelatin microspheres was significantly higher than that of their negatively charged counterparts. The absorption of sCT after intranasal and intramuscular administration was evaluated by calculating the area above the hypocalcemic-time curve (AAC) in rats. The AAC values after nasal administration of sCT in positively and negatively charged gelatin microspheres were significantly greater than that in pH 7.0 PBS. Therefore, the nasal absorption of sCT was enhanced by both types of gelatin microspheres. The hypocalcemic effect after administration of sCT in positively charged gelatin microspheres of 11.2 microm was significantly greater than that of negatively charged gelatin microspheres of the same size. On the other hand, AAC values were not affected by their particle sizes. The AAC values after the intramuscular administration of sCT in positively and negatively charged gelatin microspheres were significantly increased compared to that in PBS. Furthermore, the time-courses of the plasma calcium levels differed between positively and negatively charged gelatin microspheres. The hypocalcemic effect of the negatively charged gelatin microspheres tended to appear more slowly and last longer compared to that of positively charged gelatin microspheres. The hypocalcemic effects after intramuscular administration of sCT in gelatin microspheres were not affected by their particle sizes as well as those after intranasal administration. In conclusion, the gelatin microspheres have been shown to be a useful vehicle for nasal or intramuscular delivery of sCT.

Use of a bioabsorbable implant for the repair of severed digital flexor tendons in four horses

A new bioabsorbable implant composed of poly-L-lactic acid was used to repair the severed digital flexor tendons of four horses. The limbs were immobilised with distal casts which were changed after six to eight weeks and removed after 12 to 16 weeks. The horses were followed clinically and ultrasonographically for from seven to 19 months after the surgery. The ultrasonographic examination after the cast had been removed showed that the implants had been well incorporated into scar tissue. Two of the horses were mildly lame at the trot seven months after the surgery, but had returned to work after 12 months. The other two horses are still lame. No complications were observed with the implant.

Controlled release of vascular endothelial growth factor by use of collagen hydrogels

In vivo profile of vascular endothelial growth factor (VEGF) release from collagen hydrogels was investigated comparing that of hydrogel degradation while angiogenesis induced by the released VEGF was assessed. Collagen sponges were chemically cross-linked with different amounts of glutaraldehyde for various time periods. When 125I-labeled collagen hydrogels incorporating VEGF were subcutaneously implanted into the back subcutis of mice, the hydrogel radioactivity decreased with time, the decrement profile depending on the cross-linking conditions. The radioactivity was retained for longer time periods as the glutaraldehyde concentration and cross-linking time increased. Implantation study of collagen hydrogels incorporating 125I-labeled VEGF revealed that the remaining VEGF radioactivity decreased with time and the retention period was prolonged with the decreased hydrogel biodegradation. The slower the hydrogel degradation, the longer the period of VEGF retention. The collagen hydrogel incorporating VEGF induced significant angiogenesis around the implanted hydrogel, in marked contrast to VEGF in the solution form and VEGF-free empty hydrogel. The retention period of angiogenesis became longer with a decrease of the in vivo degradation rate of hydrogels. It is possible that the slower degraded hydrogel achieves a longer period of VEGF release, resulting in prolonged angiogenetic effect. We concluded that in our hydrogel system, biologically-active VEGF was released as a result of in vivo degradation of the hydrogel.

Soft tissue adhesive composed of modified gelatin and polysaccharides

Although fibrin glue has been clinically used as a surgical adhesive, hemostatic agent, and sealant, it has the risk of virus infection because its components, fibrinogen and thrombin, are obtained from human blood. To circumvent this problem, we employed bioabsorbable gelatin and polysaccharides to prepare a safer hemostatic glue. Gelatin was modified with ethylenediamine using water-soluble carbodiimide to introduce additional amino groups into the original gelatin, while dextran and hydroxyethyl-starch were oxidized by sodium periodate to convert 1,2-hydroxyl groups into dialdehyde groups. Upon mixing of the two polymer components in aqueous solution, Schiff base was formed between the amino groups in the modified gelatin and the aldehyde groups in the modified polysaccharides, which thus resulted in intermolecular cross-linking and gel formation. The fastest gel formation took place within 2 s, and its bonding strength to porcine skin was about 225 gf cm(-2) when 20 wt% of an amino-gelatin (55% amino) and 10 wt% of aldehyde-HES (>84% dialdehyde) aqueous solutions were mixed. In contrast, the gelation time and bonding strength of fibrin glue was 5 s and 120 gf cm(-2), respectively.

Synthetic absorbable film for prevention of air leaks after stapled pulmonary resection

Staple-line reinforcement buttresses made of bovine pericardium (BP), expanded polytetrafluoroethylene (ePTFE), and so on have been shown to be effective in preventing air leaks after stapled lung volume reduction operations, and some of them have been clinically utilized. However, each buttress suffers at least one disadvantage such as risk of viral infection and chronic inflammation. A new buttress was made using a poly(L-lactic acid-co-epsilon-caprolactone) film (L/C film) and its effectiveness as a staple-line reinforcement was examined by performing lung volume reduction operation on a canine model. Soft tissue responses to the buttress were compared with those to the BP strip and the absorbable behavior was studied. The L/C film buttress was flexible and thin enough to easily cut. Death of dogs, infection, acute and prolonged air leaks, and any complications related to its use were not observed. The tissue responses to the film were more mild and favorable than those to BP. The L/C film was absorbed after the staple line was covered by a connective tissue. The results described above suggest that the buttress made of an L/C film is a promising staple-line reinforcement material.

Influence of gelatin complexation on cell proliferation activity and proteolytic resistance of basic fibroblast growth factor

The objective of this study is to investigate the influence of gelatin complexation on the biological activity of basic fibroblast growth factor (bFGF) and its resistance to trypsin digestion. When bFGF was mixed at 37 degrees C with acidic gelatin with an isoelectric point (IEP) of 5.0, the activity to promote in vitro proliferation of BHK cells became lower compared with that of free bFGF, in contrast to mixing with the basic gelatin with an IEP of 9.0. A maximum reduction in the bFGF activity was observed for the bFGF-gelatin complex prepared at a mixing molar ratio of 1/1. The bFGF activity of cell proliferation reduced at the initial period after mixing with the acidic gelatin at 37 degrees C, followed by no substantial change. Complexation with the acidic gelatin at 4 degrees C had no influence on the bFGF activity, irrespective of the bFGF/gelatin ratio and complexation time. The biological activity of bFGF was reduced by the trypsin treatment, but the reduced extent was suppressed through gelatin complexation at 37 degrees C. In an electrophoresis study, the protective effect of gelatin complexation on the trypsin digestion was also confirmed in terms of the molecular weight loss. It is possible that the complexing gelatin covers bFGF molecules, resulting in suppression of their interaction with the cell surface receptor as well as protection from their enzymatic attack.

Acceleration of fracture healing in nonhuman primates by fibroblast growth factor-2

One of the greatest needs in the clinical bone field is a bioactive agent to stimulate bone formation. We previously reported that fibroblast growth factor-2 (FGF-2) exhibited strong anabolic actions on bone formation in models of rodents and dogs. Aiming at a clinical application, this study was undertaken to clarify the effect of a single local application of recombinant human FGF-2 on fracture healing in nonhuman primates. After a fracture was created at the midshaft of the right ulna of animals and stabilized with an intramedullary nail, gelatin hydrogel alone (n = 10) or gelatin hydrogel containing 200 microg FGF-2 (n = 10) was injected into the fracture site. Although 4 of 10 animals treated with the vehicle alone remained in a nonunion state even after 10 weeks, bone union was complete at 6 weeks in all 10 animals treated with FGF-2. Significant differences in bone mineral content and density at the fracture site between the vehicle and FGF-2 groups were seen at 6 weeks and thereafter. FGF-2 also increased the mechanical property of the fracture site. We conclude that FGF-2 accelerates fracture healing and prevents nonunion in primates, and therefore propose that it is a potent bone anabolic agent for clinical use.

Transmission electron microscopic study of hepatocytes in bioartificial liver

A bioartificial liver (BAL) was prepared by simple inoculation of hepatocytes into the inner space of hollow fibers of a hemodialyzer and it was maintained in a closed circuit for in vitro culture. Morphology of hepatocytes in the hollow fibers was studied in detail using transmission electron microscopy (TEM). The hepatocytes formed three-dimensional, rod-shaped aggregates of 200 microm in diameter throughout the whole dimension of the hollow fibers after 1 day of culture. Approximately five hepatocyte layers existed from the surface to the center of the aggregate. The hepatocytes in the aggregate displayed mostly polygonal shapes and were surrounded by five to six cells. Abundant bile canaliculi were formed between the hepatocytes and were sealed by tight junctions. The distance between the adjacent hepatocytes except the bile canaliculus domain was approximately 20 nm, and interdigitation was observed between some hepatocytes. These observations indicate that the hepatocytes formed functionally associated aggregates, that is, organoids. Although the cells facing the inner surface of the hollow fiber lost their polygonal shape and became flattened during the following several-day culture, no drastic change was observed in the morphology of the hepatocytes located inside the aggregate. After 14 days of culture, the number of living cells decreased and most of these had a deformed nucleus, few numbers of organelles, and intermittent lipid droplets.

Active drug targeting with immunoconjugates to choroidal neovascularization

PURPOSE

Active drug targeting with monoclonal antibody to neovascular vessels may be a potential treatment for choroidal neovascularization (CNV) in age-related macular degeneration (AMD). Endoglin (CD105) is a proliferating endothelial cell marker with excellent potential for targeting. The goals of this study were to investigate the expression of CD105 in CNV membranes surgically excised from patients with AMD and CNV lesions induced by intense laser photocoagulation in a cynomolgus monkey and to evaluate the in vitro effect of immunoconjugates on endothelial cells.

METHODS

CNV membranes were surgically excised from 10 patients with AMD. Experimental CNV was induced by intense laser photocoagulation in a cynomolgus monkey. Immunolocalization of CD105 on frozen sections of CNV lesions was studied by immunohistochemical evaluation. Anti-von Willebrand's factor antibody was used as an endothelial cell marker. The cytotoxic effect of immunoconjugates of anti-CD105 monoclonal antibody and dextran binding mitomycin C on human umbilical vein endothelial cells (HUVECs) was evaluated in vitro.

RESULTS

Endothelial cells demonstrated strong immunoreactivity of CD105 in all surgically excised CNV membranes. In the monkey eye, CD105-positive cells were detected only in CNV lesions but not in normal chorioretinal tissues. Immunoconjugates with anti-CD105 monoclonal antibody showed a specific inhibitory effect on proliferating HU-VECs.

CONCLUSIONS

These results suggest that anti-CD105 monoclonal antibody-mediated drug targeting has a potential to treat CNV in AMD.

Long-term follow-up study of artificial dermis composed of outer silicone layer and inner collagen sponge

In the oriental population including the Japanese, donor-site hypertrophy is more pronounced than in Caucasians. To solve the problem of donor-site morbidity and to ensure graft 'take', we started the second-stage procedure of a thin split thickness skin graft (STSG) onto acellular 'bilayer artificial skin', or 'artificial dermis'. Since reporting the original version of the material (OV), a revised version (RV) and the present version (PV, Pelnac) have been developed in stages to eliminate inconveniences associated with its use and to reduce the primary cost of manufacture. We have now used our materials, consisting of OV, RV and PV, on 52 skin defects in 41 patients. STSG took almost perfectly in all patients. The long-term results of these three materials were investigated in 20 patients who had been followed up for more than 2 years, excluding three patients whose donor sites had been directly closed. The longest and the mean follow-up periods of these patients were 12 years 5 months and 6 years 10 months, respectively. At the grafted sites, wrinkles caused by shrinkage, partial depigmentation and hypertrophy were observed in five (25%), one (5%) and one (5%) of the 20 patients, respectively. At the donor sites, slight unsightliness was observed in five (25%) of the 20 patients. Excellent or good results were obtained in 18 (90%) of the 20 patients in comprehensive evaluation. There were no significant differences in the long-term follow-up evaluations among these materials. In conclusion, the long-term postoperative appearance of the STSG site was good though a very thin (approximately 0.2mm) STSG is used; scarring of the donor site was minimal and it was possible to take repeated skin grafts from the same donor site.

Positively charged gelatin microspheres as gastric mucoadhesive drug delivery system for eradication of H. pylori

Gastric mucoadhesive drug delivery systems are very promising for eradication of Helicobacter pylori (H. pylori), a spiral bacterium that resides in the gastric mucus layer and at the mucus-epithelial cell interface. New positively charged biodegradable microspheres were prepared using aminated gelatin by surfactant-free emulsification in olive oil, followed by a cross-linking reaction with glutaraldehyde. The amino group contents of the modified gelatin and the microspheres were determined using a 2,4,6-trinitrobenzenesulfonic acid method. With the increase of glutaraldehyde concentration, the amino group content of the microspheres decreased accordingly. The influence of glutaraldehyde concentration, cross-linking reaction time, drug-loading patterns, and type of release media on the in vitro release characteristics of amoxicillin from the microspheres was investigated. Amoxicillin release rate from the modified gelatin microspheres was significantly reduced compared with that from gelatin microspheres. Furthermore, the release was decreased with the increase of glutaraldehyde concentration and/or cross-linking time. On the other hand, a faster release was observed in a lower pH release medium and/or using a lower pH solution for amoxicillin loading. The gastric mucoadhesive properties of the microspheres were evaluated using RITC-labeled microspheres in an isolated rat stomach. The gastric mucoadhesion of the modified gelatin microspheres was markedly improved compared with that of gelatin microspheres. The modified gelatin microsphere proves to be a possible candidate delivery system for the effective eradication of H. pylori.

Biodegradable scleral implant for controlled intraocular delivery of betamethasone phosphate

We evaluated nail-like, biodegradable scleral implants as a controlled intraocular delivery system of betamethasone phosphate (BP) for the treatment of chronic uveitis using pigmented rabbits. The scleral implants, which contained 10% and 25% of BP (weight 8.5 mg; length 5 mm), were made of poly (D,L-lactide-co-glycolide) (PLGA). In vivo release and retinal toxicity after implantation were also studied in pigmented rabbits. The in vitro release studies demonstrated the 10% and 25% BP-loaded scleral implants released BP in a biphasic release pattern for at least 1 month. The BP concentrations in the vitreous and the retina/choroid after application of scleral implants in pigmented rabbit eyes stayed within the concentration range capable of suppressing inflammatory responses for over 1 month. The BP concentration was greater in the retina/choroid than in the vitreous throughout the study. No substantial toxic reactions in the retina were observed by electroretinography. Our findings suggest that the BP-loaded scleral implant may be a promising device for treatment of chronic uveitis.

Modified subcutaneous tissue with neovascularization is useful as the site for pancreatic islet transplantation

The success rate of subcutaneous transplantation of pancreatic islets has been extremely low. Insufficient oxygen supply to the grafted islets is one possible major obstacle to the preservation of graft function. This study attempted to use basic fibroblast growth factor (bFGF) in subcutaneous transplantation to induce neovascularization and a sufficient blood flow around the space formed for grafted islets in the subcutaneous tissues. A bFGF-releasing device was designed enclosing bFGF in a polyethylene terephthalate mesh bag coated with polyvinylalcohol hydrogel. In the vascularized group (n = 5), two bFGF-releasing devices were implanted bilaterally into the subcutaneous tissue of the back of streptozotocin-induced diabetic Lewis rats. One week after implantation, isolated rat islets (5000) were syngeneically transplanted subcutaneously after the removal of the devices. In the control group (n = 5), no devices were implanted and the same number of rat islets was transplanted directly. One week after the implantation of the devices into the test animals, a thick, well-vascularized capsule was observed in the subcutaneous site. All vascularized recipient rats showed significant decreases in nonfasting blood glucose and maintained normoglycemia for more than 1 month after islet transplantation. However, in the control group, all rats failed to achieve normoglycemia after transplantation. This study provides evidence that the subcutaneous tissue is a promising site for pancreatic islet transplantation, offering convincing advantages in acceptability for diabetic recipients. Establishment of this subcutaneous islet transplantation technique will afford some new perspectives on successful clinical islet transplantation.