Biomedical subjects

T Kokubo

Publications and source records attributed to T Kokubo.

At least 163 records · Page 9Linked to original sources

PubMed1996

Mechanical and biological properties of two types of bioactive bone cements containing MgO-CaO-SiO2-P2O5-CaF2 glass and glass-ceramic powder.

In this study two types of bioactive bone cement containing either MgO-CaO-SiO2-P2O5-CaF2 glass (type A) or glass-ceramic powder (type B) were made to evaluate the effect of the crystalline phases on their mechanical and biological properties. Type A bone cement was produced from glass powder and bisphenol-a-glycidyl methacrylate (BIS-GMA) resin, and type B from glass-ceramic powder containing apatite and wollastonite crystals and BIS-GMA resin. Glass or glass-ceramic powder (30, 50, 70, and 80 by wt %) was added to the cement. The compressive strength of type A (153-180 MPa) and B (167-194 MPa) cement were more than twice that of conventional polymethylmethacrylate (PMMA) cement (68 MPa). Histological examination of rat tibiae showed that all the bioactive cements formed direct contact with the bone. A reactive layer was seen at the bone-cement interface. In specimens with type A cement the reactive layer consisted of two layers, a radiopaque outer layer (Ca-P-rich layer) and a relatively radiolucent inner layer (low-calcium-level layer). With type B cement, although the Ca-P-rich layer was seen, the radiolucent inner layer was absent. Up to 26 weeks there was progressive bone formation around each cement (70 wt %) and no evidence of biodegradation. The mechanical and biological properties of the cements were compared with those of a previously reported bone cement containing MgO-free CaO-SiO2-P2O5-CaF2 glass powder (designated type C).

Animals↗

PubMed1996

Quantitative assessment of apatite formation via a biomimetic method using quartz crystal microbalance.

Quantitative assessment of hydroxyapatite formation on a gold surface via the biomimetic method, composed of a nucleation step in a simulated body fluid (SBF) containing glass powders and a subsequent apatite growth step in glass powder-free SBF, was made using a quartz crystal microbalance (QCM) technique. The frequency change of the QCM linearly increased with increasing soaking time, and largely depended on the nucleation period. The growth rates, defined as daily increase in thickness, increased monotonicly with an increasing nucleation period of up to 96 h, thereafter being constant at 2.0 microns/day. The growth rate of the apatite layer increased with increasing temperature of the SBF: 0.9, 2.0, and 3.8 microns/day at 25, 37, and 50 degrees C, respectively. The Arrhenius-type activation energy for the growth of apatite was 47.3 kJ/mol. The QCM method was found to be a very powerful tool for quantitative, in situ measurement of precipitation and growth of apatite in real time.

Apatites↗

PubMed1996

Bone bonding ability of an apatite-coated polymer produced using a biomimetic method: a mechanical and histological study in vivo.

A 20-microns thick apatite layer was coated onto polyethersulfone (PES) rectangular plates by soaking them in simulated body fluid containing CaO-SiO2 based glass powder. Coated and uncoated PES plates (10 x 15 x 1.5 mm) were implanted in the tibiae of rabbits, which were sacrificed 8, 16, and 30 weeks thereafter, and the samples were examined histologically using contact microradiography (CMR), Giemsa surface staining, and a scanning electron microscope connected to an electron probe microanalyzer (SEM-EPMA). The tensile failure loads at the bone/implant interfaces were determined using the detaching test. The histological examinations showed excellent bone apposition on coated PES and the sign of degradation of the apatite layer at remodeling lacunae. The apatite layer underwent complete resorption and was replaced by bone in most areas of the bone/implant interface after 30 weeks. Bone did not bond directly to uncoated PES after each follow-up period. The failure loads between bone and coated PES at 8, 16, and 30 weeks after implantation were 1.7 +/- 0.35, 2.36 +/- 0.53, and 1.45 +/- 0.48 kg, respectively. Those between bone and uncoated PES were nearly 0 kg at each postimplantation period. Failure during the detaching test occurred at the bone/apatite interface or near it after 8 weeks. After 16 weeks, it usually occurred at the apatite/ PES interface or near it, and occasionally in the middle of the apatite layer. The apatite layer was hardly detected at the failured interface after 30 weeks. In this study, an apatite-coated PES produced using a biomimetic method was demonstrated to bond directly to bone without any intervening soft tissue, which indicates that this material possesses excellent bioactivity.

Animals↗

PubMed1996

Bone bonding behavior of titanium and its alloys when coated with titanium oxide (TiO2) and titanium silicate (Ti5Si3).

It has been proposed that the essential requirement for artificial materials to bond to living bone is the formation of bonelike apatite on their surfaces in the body. Recent studies have shown that titanium hydrogel and silica gel induce apatite formation on their surface in a simulated body fluid. In this study, the influence of titanium oxide and titanium silicate on the bonding of titanium alloys to bone was studied. Rectangular implants (15 x 10 x 2.2 mm) of titanium, Ti-6Al-4V, Ti-6Al-2Nb-Ta, Ti-6Al-4V coated with TiO2, and Ti-6Al-4V coated with Ti5Si3 were implanted into the tibial metaphyses of mature rabbits. At 8 and 24 weeks after implantation, the tibiae containing the implants were dissected out and subjected to a detaching testing. The failure load for titanium, Ti-6Al-4V, Ti-6Al-2Nb-Ta, Ti-6Al-4V coated with TiO2, and Ti-6Al-4V coated with Ti5Si3 were, respectively, 0.68 +/- 0.48, 0.22 +/- 0.46, 0.67 +/- 0.59, 2.18 +/- 0.71 and 2.03 +/- 0.41 kgf at 8 weeks, and 2.7 +/- 0.91, 2.58 +/- 1.29, 2.38 +/- 0.41, 3.79 +/- 1.7, and 2.79 +/- 0.87 kgf at 24 weeks after implantation. Histological examination by Giemsa surface staining, CMR, and SEM-EPMA revealed the coated titanium alloy implants directly bonded to bone tissue during early implantation. A Ca-P layer was observed at the interface of the coated implants and the bone. The results of this study indicated that TiO2 and Ti5Si3 can enhance the early bonding of titanium alloys to bone by inducing a Ca-P layer (chemical apatite) on the surface of titanium alloys. It also is suggested that the direct bone contact occurs in relation to the calcium and phosphorus adsorption onto the surface of the titanium passive layer formed during long-term implantation.

Alloys↗

PubMed1996

Apatite-forming ability of silicate ion dissolved from silica gels.

It is known that the prerequisite for glasses and glass-ceramics to bond to living bone is the formation of biologically active bonelike apatite on their surfaces, and a certain type of hydrated silica developed on their surfaces plays an important role in nucleating the apatite. In the present study, the apatite-forming ability of silicate ion dissolved from different silica materials into a simulated body fluid was examined as follows. Polyether sulfone substrates pretreated with O2 plasma were placed in parallel to plates of three kinds of silica gels prepared in different media and silica glass, with a distance of 0.5 mm between them in a simulated body fluid with ion concentrations nearly equal to those of human blood plasma for 4 days, and then soaked in a solution with ion concentrations 1.5 times those of the simulated body fluid for 6 days. After the first soaking, silicon combined with oxygen was detected on the surfaces of the substrates faced to all the silica gels, whereas it was not detected on that faced to the silica glass. After the second soaking, the former formed a bonelike apatite layer on their surfaces, but the latter did not. These results indicate that silicate ion which is dissolved from the silica gels and adsorbed on the substrates has an apatite-forming ability, irrespective of the microstructure of the original silica gels.

Apatites↗

PubMed1996

Preparation of bioactive Ti and its alloys via simple chemical surface treatment.

A simple chemical method was established for inducing bioactivity of Ti and its alloys. When pure Ti, Ti-6A1-4V, Ti-6A1-2Nb-Ta, and Ti-15Mo-5Zr-3A1 substrates were treated with 10M NaOH aqueous solution and subsequently heat-treated at 600 degrees C, a thin sodium titanate layer was formed on their surfaces. Thus, treated substrates formed a dense and uniform bonelike apatite layer on their surfaces in simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma. This indicates that the alkali- and heat-treated metals bond to living bone through the bonelike apatite layer formed on their surfaces in the body. The apatite formation on the surfaces of Ti and its alloys was assumed to be induced by a hydrated titania which was formed by an ion exchange of the alkali ion in the alkali titanate layer and the hydronium ion in SBF. The resultant surface structure changed gradually from the outermost apatite layer to the inner Ti and its alloys through a hydrated titania and titanium oxide layers. This provides not only the strong bonding of the apatite layer to the substrates but also a uniform gradient of stress transfer from bone to the implants. The present chemical surface modification is therefore expected to allow the use the bioactive Ti and its alloys as artificial bones even under load-bearing conditions.

Alkalies↗

PubMed1996

Apatite formation on silica gel in simulated body fluid: its dependence on structures of silica gels prepared in different media.

It has been shown that the prerequisite for glasses and glass-ceramics to bond to living bone is the formation of a layer of biologically active bonelike apatite on their surfaces. The hydrated silica formed on the surfaces of glasses and glass-ceramics plays an important role in nucleating the apatite. In the present study, the structure of the hydrated silica responsible for the apatite nucleation was investigated in an accellular simulated body fluid with ion concentrations nearly equal to those of human blood plasma. Three kinds of porous silica gels were prepared by hydrolysis and polycondensation of tetraethoxysilane in pure water or in aqueous solution containing polyethylene glycol or polyacrylic acid. The silica gels prepared in aqueous solution containing polyethylene glycol or polyacrylic acid had micron-size interconnected pores, whereas the gel prepared in pure water did not. All the gels contained a large volume of nanometer-size pores, almost the same amounts of silanol groups and D2 defect, and showed a high dissolution rate of the silica. Despite this, only the gel prepared in the solution containing polyethylene glycol formed the apatite on its surface in the simulated body fluid. This indicates that only a certain type of structural unit of the silanol group is responsible for the apatite nucleation.

Acrylates↗

PubMed1996

Analysis of anchor residues in a naturally processed HLA-DR53 ligand.

The peptide motif of the HLA-DR53 (DRB4(*)0101) molecule, which is associated with autoimmune diseases including Vogt-Koyanagi-Harada's syndrome, was determined by peptide binding assay using human L plastin p581 - 595 peptide and its substituted analogues. L plastin p581 - 595 peptide is one of the naturally processed peptides bound to HLA-DR9/DR53 (DRB1(*)0901/DRB4(*)0101) molecules. The binding affinity of each peptide to the HLA-DR53 molecule was measured by fluorescence intensity of biotinylated peptides to L cell transfectants expressing HLA-DR53 molecules, followed by treatment with avidin-fluorescence. Binding of biotinylated peptides to HLA-DR53 molecules was not inhibited by all single-alanine-substituted nonbiotinylated peptides, indicating that the replaced position was important for binding to the HLA-DR53 moleule. The inhibitory motif is considered to be an HLA-DR53-specific binding motif, composed of a positively charged residue (K) at position 1, a hydrophobic residue (I) at position 4, positively charged residue (R or K) at position 8 or 9, and another hydrophobic residue (I) at position 10. This predicted motif is different from the binding motifs of other HLA-DR molecules.

Amino Acid Sequence↗

PubMed1996

Differences of bone bonding ability and degradation behaviour in vivo between amorphous calcium phosphate and highly crystalline hydroxyapatite coating.

Three types of calcium phosphate coating were formed on polyethersulphone (PES) rectangular plates using a biomimetic method: a 20 microns thick amorphous calcium phosphate (ACP 20) coating, a 50 microns thick amorphous calcium phosphate (ACP 50) coating, and a 50 microns thick highly crystalline hydroxyapatite (hHA 50) coating. Uncoated PES plates were used as a control group. These materials were implanted in the tibiae of rabbits and subcutaneously in rats, and the samples were harvested 8 and 16 weeks thereafter, and were examined histologically. The tensile failure loads at the bone-implant interfaces were determined using the detaching test. Each ACP coating was more degradable than the hHA 50 coating. However, newly formed bone came into direct contact with underlying materials as the coating degraded. No coating degraded in subcutaneous tissue. Soft tissue intervening was seen in uncoated samples. Failure load of ACP 20-, ACP 50- and hHA 50-coated samples were all relatively higher than that of the uncoated samples at each period. Significant increase of failure load was seen in hHA 50-coated samples by 16 weeks, however, no increase was seen in either the uncoated or ACP-coated samples. If coating longevity is desired, then the hHA coating is preferable. However, if only the osteoconducive property of calcium phosphate coating is desired for initial fixation of porous materials, the ACP coating may be advantageous.

Animals↗

PubMed1996

Ultrastructural study of an apatite layer formed by a biomimetic process and its bonding to bone.

A dense and uniform apatite layer about 20 microns thick was formed on a poly(ether sulphone) (PESF) substrate treated with glow discharge in O2 gas by a biomimetic process. The apatite-polymer composite obtained was implanted into a rabbit tibia and the structure of the PESF-apatite-bone interface was observed under a scanning and a transmission electron microscope 8 weeks after implantation. The apatite layer formed by the biomimetic process was confirmed to consist of small crystals of apatite with a structure similar to that of apatite in bone. The apatite layer remained on the substrate in the body, and bonded to the apatite in bone directly. This type of apatite-organic polymer composite expected to be useful as bone-repairing material.

Animals↗

PubMed1996

Antibacterial activity of silver ions implanted in SiO2 filler on oral streptococci.

OBJECTIVE: To evaluate the role of silver ions in composite resin dental materials, an in vivo investigation was conducted into the antibacterial effect of SiO2 filler implanted with silver ions on oral streptococci. METHODS. SiO2 filler samples (0.1g) were implanted with silver ions. The effect of the filler with silver ions (Ag+ filler) was tested on oral streptococci bacteria. These bacterial strains had been isolated predominantly from composite resin surfaces. The organisms tested were anaerobically cultured in 5 mL Trypticase Soy Broth containing 0.5 per cent yeast extract at 37 degrees C for 10-12 h. Each bacterial strain was adjusted to a concentration of 1 x 10(6) cells per mL with reduced transport fluid (RTF). Ag+ filler was immersed in 1 mL of RTF and anaerobically incubated 2, 6 and 12 h to study the antibacterial effect. The survival of bacteria was then estimated by culturing on TSBY agar plates. A plate with approximately 100 discrete colonies was chosen from the serial agar cultures, and the number of colonies was counted at each sampling time. RESULTS: The Ag+ filler showed significantly more antibacterial activity than the control filler without silver ions. SIGNIFICANCE: These results indicate that the antibacterial effect found in this study was due to the silver ions released by the Ag+ filler and that it may be useful to add this filler to composite resin dental materials for secondary caries protection.

Anti-Infective Agents, Local↗

PubMed1996

Abundance of Gal beta 1,3GalNAc in O-linked oligosaccharide on hinge region of polymerized IgA1 and heat-aggregated IgA1 from normal human serum.

Gas-phase hydrazinolysis was used to analyze the glycoform of the O-linked oligosaccharide of human serum IgA1. In our previous report, only one glycoform was obtained from the IgA1 of healthy individuals. However, it was found to be composed of heterogeneous IgA1 components having mutually different glycoforms. First, the IgA1 was separated into two subfractions having different affinities toward jacalin. Among them, the high-affinity subfraction was mainly composed of polymerized IgA1. Comparative study of the carbohydrate chain showed a relative abundance of Gal beta 1,3GalNAc in the polymerized form. A simultaneous analysis of the N-glycan of these subfractions was also carried out. Three major components, two biantennary and one triantennary oligosaccharides, were obtained from both subfractions and the relative contents of these components were almost the same. On the other hand, IgA1 was artificially polymerized by heating at 63 degrees C for 2 h. The heat-stable IgA1 was separated from the heat-aggregated material on a Sephacryl S-300 column. The obtained heat-stable IgA1 (approximately 20%) was not further aggregated by more heating under the same conditions. The heat-stable IgA1 contained a much higher amount of the sialylated Gal beta 1,3GalNAc. Thus, it was shown that the degree of completeness of the hinge O-linked oligosaccharide might be correlated with the stability and polymerization process of the IgA1 molecule.

Acetylgalactosamine↗

PubMed1996

Estimation of the number of O-linked oligosaccharides per heavy chain of human serum IgA1 by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOFMS) analysis of the hinge glycopeptide.

In our previous study, gas-phase hydrazinolysis was used to analyze the glycoform of the O-linked oligosaccharide of human serum IgA1. All O-linked oligosaccharide chains are known to be present in the hinge portion. However, the number of O-linked oligosaccharide chains on IgA1 remained unclear. In order to determine the number of linked sugar chains, we applied matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOFMS) to the hinge glycopeptide prepared from human serum IgA1. MALDI-TOFMS did not show clear peaks, probably due to the microheterogeneity of the structure of each sugar chain. However, elimination of peripheral sialic acid and galactose residues by sequential treatment with neuraminidase and beta-galactosidase gave clear mass spectra with several sharp peaks. On the basis of these spectra, we conclude that IgA1 prepared from normal human serum carries different numbers of sugar chains. There are two major populations, one contains five GalNAc residues and the other four GalNAc residues. On the other hand, the hinge glycopeptide prepared from myeloma IgA1 was composed mainly of one population containing four GalNAc residues. Earlier, we reported incomplete glycosylation of IgA1 isolated from the serum of an IgA1 myeloma patient. In this experiment, the presence of four O-linked oligosaccharides per heavy chain of IgA1 from a myeloma patient was found. The reason why only four out of five sites on the hinge glycopeptide were fully glycosylated in the IgA1 from the IgA1 myeloma patient is not clear.

Amino Acid Sequence↗

PubMed1996

Steroid therapy during the early stage of progressive IgA nephropathy. A 10-year follow-up study.

This study was undertaken to clarify the effect of corticosteroids on the long-term clinical course of the early stage of progressive IgA nephropathy. The early stage of progressive IgA nephropathy was defined as having moderate proteinuria between 1 and 2 g/day, creatinine clearance values of 70 ml/min or more, and a histological severity score of 7 or more. The number of patients who fulfilled these three conditions during 12 years from 1972 and then were continuously followed up for 10 years or more in our renal unit was 46. Twenty of them received steroid treatment for an average period of 18 months, and the remaining 26 patients had no steroid treatment. The initial data of proteinuria, creatinine clearance values, frequency of hypertensive cases, and histological scores of 7 or more were not different between the two groups: 1.4 +/- 0.4 vs. 1.3 +/- 0.3 g/day, 85 +/- 14 vs. 88 +/- 13 ml/min, 25 vs. 38%, and 10.7 +/- 2.5 vs. 11.0 +/- 3.0, respectively. During the follow-up period of 10 years, the renal survival rate was significantly different between the two groups (100 vs. 84% 5 years after starting therapy and 80 vs. 34% 10 years later; p < 0.001). The final creatinine clearance values were significantly different between the two groups (54 +/- 35 vs. 20 +/- 29 ml/min; p < 0.005). On the other hand, the patient groups with mild histological changes or decreased renal function due to moderate proteinuria showed no significant differences in the final outcome. These results indicate that corticosteroids are beneficial in stabilizing the renal function for a long time during the early stage of progressive IgA nephropathy, although this study was not a randomized one.

Adult↗

PubMed1996

Lipoprotein derangement during steroid treatment in minimal-change nephrotic syndrome.

To study the pathophysiology of hyperlipidemia in nephrotic syndrome, we compared lipid metabolism in the nephrotic stage (stage 1) and in stage 2, when albuminuria had subsided, in 11 patients with minimal-change disease treated with corticosteroid. High-density lipoprotein (HDL) levels were decreased and HDL contained more cholesterol and triglyceride per unit of protein in stage 1 in the patients than in age-matched healthy controls. The urinary protein level was positively correlated only with low-density lipoprotein (LDL) levels, suggesting that the increased albumin clearance stimulated LDL production. Serum cholesterol levels were positively correlated with apolipoprotein E levels and were negatively correlated with lecithin-cholesterol acyltransferase activity in the nephrotic stage; the opposite correlations were seen in controls. Although triglycerides in HDL had normalized at stage 2, triglycerides in LDL and very-low-density lipoprotein did not return toward normal until stage 3, when serum cholesterol levels were normalized.

Adult↗

PubMed1996

Association of asialo-galactosyl beta 1-3N-acetylgalactosamine on the hinge with a conformational instability of Jacalin-reactive immunoglobulin A1 in immunoglobulin A nephropathy.

The O-glycans in Jacalin-binding immunoglobulin A1 (IgA1) were released by gas-phase hydrazinolysis and were fractionated by gel filtration and reversed-phase HPLC. Four peaks (P1 to P4) were obtained. There was a significant shift from Peak 2 (monosialylated Gal beta 1-3GalNAc) to Peak 4 (asialo-Gal beta 1-3GalNAc) in the IgA-nephropathy group compared with the negative control group (P < 0.05). One of the functions of the carbohydrate side chains is to stabilize the three-dimensional structure of the glycopeptides. In order to evaluate the stability of the Jacalin-binding IgA1 molecule, the increase in turbidity as a consequence of the increase of the aggregated IgA1 level under the condition of high temperature (63 degrees C) was observed. The increase in the turbidity was significantly higher in the IgA nephropathy group compared with the negative control group (21.7 vs. 5.9% at 150 min, P < 0.02). From a sample of IgA1 solution that had originated from a pooled normal serum, heat-tolerant (nonaggregated) and intolerant (aggregated) IgA1 molecules were separated by gel filtration. The heat-intolerant IgA1 had lower amounts of sialic acid (27.4 micrograms/mg IgA1) than the tolerant IgA1 (37.6 micrograms/mg IgA1). Further, the analysis of the O-glycans released from another IgA1 sample by the hydrazinolysis revealed that the ratio of the asialo-Gal beta 1-3GalNAc/total Gal beta 1-3GalNAc in the heat-in-tolerant IgA1 (27.2%) was increased compared with that in the heat-tolerant IgA1 (18.2%). From these results, it was suggested that unusual glycosylation on the hinge region of Jacalin-binding IgA1 induced an insufficient conformational stiffness to the hinge peptide, resulting in the aggregation of the IgA1 molecule in IgA nephropathy.

Acetylgalactosamine↗

PubMed1996

[Expression of major histocompatibility complex of advanced non-small cell lung cancer (NSCLC)].

Expression of major histocompatibility complex of lung cancer was examined to study the malignant potential of the tumor using immunochemical staining (anti-HLA class I monoclonal antibody; w6/32). Nuclear DNA contents and the labeling index of proliferating cell nuclear antigen (PCNA) were measured as well. Forty three advanced (p-stage IIIa) lung cancers resected by lobectomy (33 cases), pneumonectomy (9 cases), and segmentectomy (1 case) entered the study. Mediastinal lymph node dissection was performed in every case during the operation. Of the 43 cases, expression of HLA class I was positive in 17 and negative in 26. The patients with positive HLA expression showed significantly better prognosis than those with negative HLA expression in terms of 5 year survival (p < 0.01). The patients with aneuploid pattern and positive HLA class I expression had the best prognosis on the survival curve (p < 0.01). When the PCNA positive rate was high, the prognosis was poor. And the patients with negative PCNA and positive HLA class I expression had significantly better prognosis than the others (p < 0.01). These findings suggest that the expression of HLA class I on the tumor cells is an important prognostic factor in the patients with NSCLC.

Carcinoma, Non-Small-Cell Lung↗

PubMed1995

Sequential analysis of gene expression after an osteogenic stimulus: c-fos expression is induced in osteocytes.

We have recently developed an experimental model whereby mechanical stimulation induces osteogenesis in the caudal vertebrae of rats. We used this model to assess expression of genes induced by mechanical loading. Bulk preparations of mRNA extracted after loading did not show > 2-fold increases in expression of mRNA for matrix proteins or growth factors in Northern blotting analysis. c-jun was undectable. However, c-fos showed a 4-fold increase in expression within 60 mins of loading, before returning to control levels by 4 hrs. This increase was associated with intense signals in in situ hybridization, not seen in any nonloaded vertebrae, for c-fos over cortical osteocytes: thus osteocytes respond to mechanical loading with c-fos expression so strongly as to be visible even in the bulk RNA preparations. The results represent persuasive evidence for a role for osteocytes, and for c-fos, in the osteogenic response of bone to mechanical stimulation.

Animals↗