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Hiroo Iwata

Publications and source records attributed to Hiroo Iwata.

49 records · Page 3Linked to original sources
PubMed2003

Dextran sulfate as a material for the preparation of a membrane for immunoisolation.

Bioartificial pancreas, in which the islets of Langerhans (islets) are enclosed in an artificial membrane to be protected from the host immune system, is expected to be a promising medical device to treat patients who suffer from insulin-dependent diabetes. Our strategy for preparation of a bioartificial pancreas involves utilizing a membrane including polymeric materials that can inhibit the complement. In our series of studies, we have examined interactions of various polyanions with the complement system to search for potential complement inhibitors. In this study, we concentrated our efforts to clarify the effects of dextran sulfate on the complement system. All of the dextran sulfates examined inhibited the complement activation through both classical and alternative pathways as previously reported. In addition to their inhibitory effects, a certain species of dextran sulfate (molecular mass 10 kDa, degree of sulfonation in a pyranose ring 1.99) specifically degraded C3 without complement activation and, thus, anaphylatoxins that trigger inflammatory reactions were not generated. These facts suggest that a membrane including dextran sulfate effectively protects the islet cells from humoral immunity in addition to not triggering inflammatory reactions. These properties of the membrane make it suitable for a bioratificial pancreas.

Bioartificial Organs↗
PubMed2003

Effect of adsorbent of Riposorber, a cellulose microparticle with immobilized dextran sulfate, on the serum complement system.

Abstract-Apheresis. using columns of cellulose microparticles with immobilized dextran sulfate, Riposorber, has been applied to treatment of patients with various diseases, such as hypercholesterolemia and systemic lupus erythematosus. Unfortunately, it has been reported that the apheresis activates the complement system. It might exert unpleasant side effects on patients during lifelong treatment. In this study, the interaction of the serum complement system with cellulose microparticles with immobilized dextran sulfate and its components, nontreated cellulose microparticles and dextran sulfate, were examined in vitro to get some ideas for development of an extracorporeal apparatus which does not give any serious damage to patient blood. The cellulose microparticles with immobilized dextran sulfate reduces both the CH50 and the ACH50. Decrease in CH50 is not due to the classical pathway activation, but to adsorption of C2 or Cl components including Clq. The alternative pathway was not activated by the addition of the dextran sulfate alone to serum, but the addition of non-treated cellulose microparticles to serum activated complement. Form these, decrease in ACH50 is not caused by dextran sulfate on the microparticles, but by the hydroxyl groups of the cellulose microparticles that is the core of the column. For prevention of complement activation, hydroxyl groups remaining after dextran sulfate immobilization should be blocked by further treatment with a reagent that reacts with them, or else dextran sulfate might be immobilized on particles without nucleophiles such as hydroxyl or amino groups.

Cellulose↗
PubMed2002

Adhesion between poly(ethylene-co-vinyl alcohol) (EVA) and titanium.

Lap shear adhesive strength between titanium and various kinds of commercial polymers was evaluated. Among them, poly(ethylene-co-vinyl alcohol) (EVA) showed the highest strength. The results of electron spectroscopy for chemical analysis and the contact angle to water indicated that the high adhesive strength of EVA might be due to its high hydrophilicity. Water resistance of adhesion by water immersing at 37 degrees C was investigated. In the case of polyurethane-titanium, the adhesive strength decreased immediately. In contrast, EVA-titanium kept its initial adhesive strength for at least up to 1 month. It was confirmed that surface modification of titanium by hydrogen peroxide enhanced the adhesive and peeling strength. It was based on not only an increase in surface adhesive area but also an increase in the hydrophilicity of titanium by the production of Ti-OH.

Adhesiveness↗
PubMed2002

Evaluation of the antiadhesion potential of UV cross-linked gelatin films in a rat abdominal model.

Among five kinds of rat adhesion models tested, the following model was selected. The epigastric vein 2.5 cm from the midline of the abdomen was cut by sharp scissors, and the lateral side of the cut epigastric vein was ligated using a 3-0 silk suture. This model could be easily prepared and gave a rate of adhesion formation of 90%, which was useful for screening antiadhesive materials. For the kinetic study of tissue adhesion in this model, an injured site was covered with a non-degradable poly(vinyl alcohol) (PVA) film. The incidence rate of adhesion was 18%, when the PVA film covered the injured site for 2 days. This suggests that an antiadhesive barrier should cover the injured site for at least 2 days. The antiadhesion efficacy of cross-linked gelatin films were evaluated using this adhesion model. The UV cross-linked gelatin film which was designed to exist for 2 days but to disappear at day 3 in the rat abdominal cavity showed the highest antiadhesion efficacy.

Abdominal Cavity↗
PubMed2002

Xenotransplantation of pig islets in diabetic dogs with use of a microcapsule composed of agarose and polystyrene sulfonic acid mixed gel.

INTRODUCTION: The authors have designed a microcapsule composed of agarose and polystyrene sulfonic acid (PSSa) mixed gel that provides a protective barrier against complement attack. Xenografts of islets, encapsulated in an agarose-PSSa microcapsule, have been shown to normalize blood glucose in rodents with chemically induced diabetes for extended periods of time without immunosuppression. AIM: To investigate the efficacy of agarose-PSSa microencapsulated pig islets in reversing diabetes in a large animal model. METHODOLOGY: Diabetes was induced in beagle recipients by total pancreatectomy. Each recipient received three to five intraperitoneal injections of either encapsulated (n = 5) or nonencapsulated pig islets (n = 2). RESULTS: In all dogs receiving microencapsulated islets, the graft function was achieved for 7.4 +/- 3.1 weeks (mean +/- standard error), as determined by elimination or reduction of exogenous insulin requirement. In three recipients, the fasting blood glucose levels were maintained at < or = 200 mg/dL without any exogenous insulin for a period of 6, 50, and 119 days. Circulating porcine C-peptide was detected in the sera of all dogs after transplantation of encapsulated islets. Immunohistologic examination revealed the presence of insulin-positive cells in the microcapsules. In contrast, in two dogs receiving nonencapsulated islets there was no graft function. CONCLUSIONS: This preliminary study demonstrates that agarose-PSSa microencapsulated pig islets can survive and function for weeks or months in totally pancreatectomized diabetic dogs without immunosuppression.

Animals↗
PubMed2002

Improving function and survival of porcine islet xenografts using microencapsulation and culture preconditioning.

INTRODUCTION AND AIMS: Porcine pancreatic islets have been difficult to preserve because isolated porcine islets tend to disaggregate to single cells and lose function under culture conditions. In the current study, the influence of agarose microencapsulation on the maintenance of the number and function of islets in culture preservations and the effect of culture preconditioning of microencapsulated porcine islets on xenogenic transplantation were investigated. METHODOLOGY: Porcine islets were isolated and then microencapsulated in 5% agarose membrane. The percentage of naked and microencapsulated islets remaining in the culture preservations was assessed. The effect of microencapsulation and culture on secretory function was investigated in vitro. The survival of overnight-cultured and 7-days-cultured microencapsulated islets in xenogenic transplantations was examined. RESULTS: A good percentage of microencapsulated islets remained in the culture preservations. They could maintain good secretory functions in vitro after 7 days of culture. In addition, we observed a significant prolongation of mean islet survival by culture preconditioning. CONCLUSIONS: The present findings suggest that microencapsulation is one of the useful preserving methods for maintenance of the number and function of cultured isolated porcine islets. Moreover, culture preconditioning is effective for improving islet survival and might be a good option leading to clinical success.

Animals↗
PubMed2002

A mixture of ethylene vinyl alcohol copolymer and ethanol yielding a nonadhesive liquid embolic agent to treat cerebral arteriovenous malformations: initial clinical experience.

OBJECT: The authors report their clinical experience with their new nonadhesive liquid embolic agent, an ethylene vinyl alcohol copolymer (EVAL)/ethanol mixture, to treat arteriovenous malformations (AVMs). METHODS: Between June 1995 and April 2001, 57 patients with confirmed AVMs underwent embolization of their lesions with the EVAL/ethanol mixture. In 87 procedures consisting of one to three stages, the authors embolized 185 feeding arteries to occlude as much of the AVM as possible. Repeated injections under fluoroscopic control could be performed smoothly without encountering cementing of the catheter to the vessel wall. Among the 87 embolizations undertaken in 57 patients, seven procedures (8%) in six patients produced new postembolization symptoms. Resolution of these symptoms occurred within hours or days after four of the seven procedures; permanent neurological deficits remained after the other three procedures (3.4%). Of the 57 patients, three underwent postembolization radiosurgery, and 54 underwent radical treatment with microsurgical extirpation. Histopathological examination of the 54 specimens disclosed mild inflammation within the embolized lumen without inflammatory reactions in the media or adventitia. Follow-up angiograms obtained 3 years after radiosurgery was administered showed that in all three patients treated in this fashion the nidus had completely disappeared. CONCLUSIONS: The EVAL/ethanol mixture is handled easily and appears to be an effective and safe agent for preoperative embolization of AVMs.

Adolescent↗
PubMed2002

A nonadhesive liquid embolic agent composed of ethylene vinyl alcohol copolymer and ethanol mixture for the treatment of cerebral arteriovenous malformations: experimental study.

OBJECT: The authors have developed a mixture of ethylene vinyl alcohol copolymer (EVAL) and iopamidol, which is dissolved in ethanol, as an alternative solvent to provide a safe means of embolizing arteriovenous malformations (AVMs). METHODS: A two-stage delivery technique is required to prevent premature precipitation in the catheter when using this material: the catheter is first infused with 30% ethanol and this is followed by the delivery of the EVAL-ethanol mixture. Acute angiographic changes were analyzed after superselective delivery of dimethyl sulfoxide (DMSO) and 30% ethanol into the renal artery of rabbits. Histological changes following the embolization of the renal artery achieved using the EVAL-ethanol mixture were recorded at 1 hour and at 2 and 16 weeks after the procedure. Although DMSO always produced severe, rapidly progressive vasospasm in the renal artery during a 1- to 60-minute postinfusion, 30% ethanol did not. Microscopically, the lumens of embolized vessels examined 1 hour after embolization with EVAL-ethanol appeared to be filled with EVAL sponges, leaving almost no open spaces. The space between the EVAL sponges and the inner surface of the vessels was filled with fresh thrombus. In the vessel walls of specimens examined 2 weeks after embolization there was no or a slight inflammatory reaction. Scattered in the EVAL sponges were almost equal numbers of neutrophilic granulocytes and mononuclear cells, indicative of a mild inflammatory response. In specimens examined 16 weeks postembolization, the changes noted at 2 weeks were intensified. There was no definite histopathological evidence of mural hemorrhage, perivascular extravasation of the mixture, or perivascular hemorrhage in any specimen that was examined. CONCLUSIONS: Although the degree of permanence of this embolization material is yet unknown, the mixture was easy to handle, and appeared safe and effective for AVM embolization. Its nonadhesive characteristic and its ability to be infused by repeated injections make it an attractive alternative to currently available materials. The good results obtained in this study led us to undertake a clinical trial, the results of which are contained in a companion article in this issue of the Journal of Neurosurgery.

Animals↗
PubMed2002

Beta-tricalcium phosphate as a substitute for autograft in interbody fusion cages in the canine lumbar spine.

OBJECT: An interbody fusion cage has been introduced for cervical anterior interbody fusion. Autogenetic bone is packed into the cage to increase the rate of union between adjacent vertebral bodies. Thus, donor site-related complications can still occur. In this study a synthetic ceramic, beta-tricalcium phosphate (TCP), was examined as a substitute for autograft bone in a canine lumbar spine model. METHODS: In 12 dogs L-1 to L-4 vertebrae were exposed via a posterolateral approach, and discectomy and placement of interbody fusion cages were performed at two intervertebral disc spaces. One cage was filled with autograft (Group A) and the other with TCP (Group B). The lumbar spine was excised at 16 weeks postsurgery, and biomechanical, microradiographic, and histological examinations were performed. Both the microradiographic and histological examinations revealed that fusion occurred in five (41.7%) of 12 operations performed in Group A and in six (50%) of 12 operations performed in Group B. The mean percentage of trabecular bone area in the cages was 54.6% in Group A and 53.8% in Group B. There were no significant intergroup differences in functional unit stiffness. CONCLUSIONS: Good histological and biomechanical results were obtained for TCP-filled interbody fusion cages. The results were comparable with those obtained using autograft-filled cages, suggesting that there is no need to harvest iliac bone or to use allo- or xenografts to increase the interlocking strength between the cage and vertebral bone to achieve anterior cervical interbody fusion.

Animals↗
PubMedDate not supplied

Fabrication of cell-based arrays using micropatterned alkanethiol monolayers for the parallel silencing of specific genes by small interfering RNA.

The emergence of small interfering RNA (siRNA) opened a new opportunity to study gene functions in a genome. However, large-scale loss-of-function analyses further require cell-based high-throughput methods that allow simultaneous silencing of the huge number of genes by siRNA. In this study, we aim at fabricating the cell-based siRNA arrays that facilitate parallel introduction of multiple siRNAs into cultured mammalian cells. The siRNA arrays were prepared using surface chemical processes including the micropatterning of a self-assembled monolayer and the layer-by-layer assembly of siRNA and cationic lipid. We examined the feasibility of the siRNA array for the sequence-specific gene silencing in an array format. Furthermore, the effects of siRNA loading and culture period after transfection were studied to optimize cell-based assays on the siRNA arrays. The results obtained in this study demonstrated that our method provides the siRNA arrays with spatial specificity in gene silencing, which will serve to obtain a quantitative data set from the cell-based screens on siRNA arrays.

Base Sequence↗
PubMedDate not supplied

CirculaFloor.

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Computer Graphics↗
PubMedDate not supplied

Bioartificial liver with whole blood perfusion.

In our series of studies, we have made an effort to develop a bioartificial liver (BAL) system through which whole blood can be perfused as in hemodialysis therapy. In this study, BAL cartridges containing porcine hepatocytes were prepared and perfused in an extracapillary space with human whole blood in vitro. Lidocaine loading tests were performed to evaluate the detoxification ability of the BAL. The clearance value of lidocaine decreased during the initial 6 hours to about 50% of the initial value. After that, it was almost stable until 48 hours. After 48 hours perfusion, thin sections of the hollow fibers containing hepatocytes were prepared and stained with hematoxylin-eosin and immunohistochemically stained for membrane attack complex (MAC). The porcine hepatocytes formed aggregates in the hollow fibers, nuclei in the cells were observed clearly, and MAC was not seen on the porcine hepatocyte aggregation. A hollow fiber that can reject 90% of molecules with molecular weight of 50 kDa effectively protects porcine hepatocytes from humoral immunity. The in vivo assessment of the BAL cartridge was performed using a canine model for 24 hours. No significant hemolysis or thrombus that affected the BAL system and the canine were observed. These results suggest that our BAL system is a promising liver assist device through which patients' whole blood can be perfused.

Animals↗