Search PubMed⌕ Search

Biomedical subjects

M Oka

Publications and source records attributed to M Oka.

At least 271 records · Page 15Linked to original sources
PubMed1996

Bone remodeling around implanted ceramics.

Bone formation and remodeling around implanted materials is influenced by the kind of material, its surface properties, and the anatomical site of implantation. In this study, differences in bone formation around three kinds of ceramics and the importance of the implant location in the tibia were investigated. In the first experiment, we placed three kinds of ceramics--alumina, zirconia and hydroxyapatite (HA)--into the medullary cavity of rabbit tibiae and examined histologically the time-dependent formation of bone around the materials for up to 24 weeks postoperatively. We found that bone formation depends on whether or not the materials are in direct contact with the endosteum. In the second experiment, the same three ceramic materials were implanted transcortically into rabbit tibiae. The bone formed around the implants was most abundant in regions adjacent to the periosteum, followed by the endosteum and the marrow cavity in the approximate ratios of 70%, 40%, and 10%, respectively. In these two experiments, the difference between bioactive and bioinert ceramics could be seen in the interface between the implanted material and the bone. It can be concluded that bone formation around these materials is related to the osteoconductivity of the materials and to the osteogenic capacity of the tissues.

Aluminum Oxide↗
PubMed1996

Bone-bonding behavior of plasma-sprayed coatings of BioglassR, AW-glass ceramic, and tricalcium phosphate on titanium alloy.

The bone-bonding behavior of three kinds of bioactive ceramics coated on titanium alloy by the plasma-spray technique was investigated. Titanium alloy (Ti-6A1-4V) coated with BioglassR (45S5), apatite-wollastonite containing glass ceramic (AW), or beta-tricalcium phosphate (TCP) was prepared, and rectangular specimens were implanted into the tibial bones of mature male rabbits, which were sacrificed 8 or 24 weeks after implantation. The tibiae containing the implants were dissected out and subjected to detachment tests to measure the failure load. The bone-implant interface was investigated by Giemsa surface staining, contact microradiography, and scanning electron microscopy-electron probe microanalysis (SEM-EPMA). Eight weeks after implantation, the failure loads for implants coated with BioglassR, AW, and TCP were 1.04 +/- 0.94, 2.03 +/- 1.17, and 3.91 +/- 1.51 kg, respectively, and 24 weeks after implantation, the respective failure loads were 2.72 +/- 1.33, 2.39 +/- 1.30, and 4.23 +/- 1.34 kg. Failure loads of AW- and TCP-coated implants did not increase significantly with time. After the detachment test, breakage of the coating layer was observed. Bioactive ceramics can act as stimulants that induce bonding between bone and metal implants. However, failure load of metal implants coated with the bioactive ceramics was lower than that of bulk AW or TCP. It appears impossible to obtain a higher failure load using a bioactive-ceramic coating on titanium alloy. Histologically, the coating layer was found to become detached from the metal implant and the bone tissue bonded to the coating layer. SEM-EPMA observation revealed breakage of the coating layer, although bonding between bone and the coating layer was evident. A Ca-P-rich layer was observed at the interface between bone and the AW coating, and a Ca-P-rich and a Si-rich layer were observed at the interface between bone and the BioglassR coating. For clinical application, it would seem better to use coated metal implants for short-term implantation. However, there is a possibility of breakage of the coating layer because of both dissolution of the bioactive ceramic and mechanical weakness at the interface between the coating layer and the metal implant.

Alloys↗
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

Deletion of specific protein kinase C subspecies in human melanoma cells.

It has been shown that tumor-promoting phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA), stimulates the proliferation of normal human melanocytes, whereas it inhibits the growth of human melanoma cell lines. The expression of protein kinase C (PKC) subspecies, the major intracellular receptors for TPA, was examined in normal melanocytes and the four melanoma cell lines HM3KO, MeWo, HMV-1, and G361. PKC was partially purified and then separated into subspecies by column chromatography on Mono Q and hydroxyapatite successively, and finally subjected to immunoblot analysis using antibodies specific for the PKC subspecies. Of the PKC subspecies examined, delta-, epsilon-, and zeta-PKC were detected in both normal melanocytes and the four melanoma cell lines. In contrast, both alpha-PKC and beta-PKC were expressed in normal melanocytes, whereas either alpha-PKC or beta-PKC was detected in melanoma cells. Specifically, HM3KO, MeWo, and HMV-1 cells were shown to contain alpha-PKC but not beta-PKC, while G361 cells expressed beta-PKC but not alpha-PKC. The growth of these melanoma cells was suppressed by TPA treatment, and the growth of the G361 cells lacking alpha-PKC was inhibited more efficiently than the other melanoma cell lines which lacked beta-PKC. It was further shown that beta-PKC was not detected in freshly isolated human primary or metastatic melanoma tissues. These results suggest that the expression of alpha-PKC or beta-PKC may be altered during the malignant transformation of normal melanocytes and that loss of alpha-PKC or beta-PKC may be related to the inhibitory effect of TPA on the growth of melanoma cells.

Cell Division↗
PubMed1996

Differential requirements for Ca2+ concentrations for catecholamine release and biosynthesis in isolated bovine adrenal chromaffin cells.

Differential effects of [Ca2+] on catecholamine release and biosynthesis in isolated bovine adrenal chromaffin cells were investigated. Carbamylcholine, an agonist of the nicotinic and muscarinic acetylcholine receptor, or Na+ deprivation in the incubation medium, stimulated catecholamine release and biosynthesis in these cells. The concentrations of extracellular [Ca2+] which stimulate catecholamine biosynthesis were less than those which stimulate catecholamine release. An increase in intracellular levels of free Ca2+ ([Ca2+]i) induced by Na+ deprivation was dependent on extracellular [Ca2+]. These results indicate that, in bovine adrenal chromaffin cells, catecholamine biosynthesis is regulated by lower levels of [Ca2+]i than is catecholamine release.

Adrenal Medulla↗
PubMed1996

Effect of 4G-beta-D-galactosylsucrose (lactosucrose) on fecal microflora in patients with chronic inflammatory bowel disease.

Metabolic interaction between the intestinal microflora and the host has been suggested to play a role in the pathogenesis of chronic inflammatory bowel disease. Elemental or low-fat, low-residual diets in patients with Crohn's disease or ulcerative colitis are reported to decrease anaerobic bacteria and to change the composition of the intestinal microflora. We examined the effect of an indigestible agent, 4G-beta-D-galactosylsucrose (lactosucrose), which is selectively utilized by intestinal Bifidobacterium, on the composition of the intestinal microflora. After the administration of lactosucrose to two patients with Crohn's disease and five patients with ulcerative colitis for 2 weeks, significant induction of the growth of Bifidobacterium was observed, and significant reduction in the population level of Bacteroidaceae was seen. Bowel movements improved in four patients. The intestinal environment, estimated by measuring fecal pH, fecal levels of short-chain fatty acids and putrid products, and the urinary secretion of indican, also improved in these patients. These results suggest that lactosucrose may be useful for patients with chronic inflammatory bowel disease.

Adolescent↗
PubMed1996

T cell receptor V alpha and V beta gene usage by tumour-infiltrating lymphocytes in oral squamous cell carcinoma.

Oral squamous cell carcinomas (SCC) are often infiltrated by a large number of T lymphocytes. To clarify the nature of the tumour-infiltrating lymphocytes (TIL), we examined T cell receptor (TCR) V alpha and V beta gene usage by TIL and peripheral blood mononuclear cells (PBMC) obtained from 10 patients with oral SCC. We obtained RNA from TIL and PBMC, synthesized complementary DNA, and used the polymerase chain reaction (PCR) method with a panel of primers specific for the V gene segment subfamily (V alpha 1-18/V beta 1-20). We thus found that TIL showed more restricted usage of V beta gene families in contrast to PBMC of the same patients while two unique V beta gene (V beta 6 and V beta 5.2) segment transcripts were overexpressed in the TIL of more than half of the patients. On the other hand, no major difference was observed in the V alpha gene usage between the TIL and PBMC of most patients. To characterize these T cell subpopulations with unique V beta gene segment transcripts further, we sequenced the complementarity-determining region 3 in V beta 6-C beta and V beta 5.2-C beta PCR products derived from TIL and PBMC of two selected patients in each case. Although no usage of the conserved amino acid sequence by TIL was detected, the frequent use of V beta 6/J beta 1.1 in one patient and the V beta 6/J beta 2.7 gene segments in another patient was observed. Regarding the V beta 5.2 transcripts, obtained from the other two patients, no preferential usage of specific J beta gene segments by TIL was observed. These results suggest that the unique T cell populations are amplified in patients with oral SCC, possibly as a consequence of an in situ immune reaction.

Adult↗
PubMed1996

Optimal schedule for administering granulocyte colony-stimulating factor in chemotherapy-induced neutropenia in non-small-cell lung cancer.

A prospective randomized study was conducted to determine the optimal schedule of rhG-CSF (recombinant human granulocyte colony-stimulating factor). A group of 33 lung cancer patients treated with MVP therapy (mitomycin, vindesine, and cisplatin) were randomly assigned to three groups: an early prophylaxis group in which rhG-CSF was initiated on day 2 of the MVP cycle; a late prophylaxis group in which rhG-CSF was initiated on day 8; and a therapeutic group in which rhG-CFS was initiated after the onset of neutropenia. Ten patients who had received MVP therapy without rhG-CSF were also analyzed as a no-support group. The incidence of neutropenia was 80% (16/20 courses) in the early prophylaxis group, 44% (8/18) in the late prophylaxis group, 94% (17/18) in the therapeutic group, and 94% (16/17) in the no-support group. The incidence of neutropenia in the late prophylaxis group was less than in the early prophylaxis group (P<0.05), the therapeutic group (P<0.01), and the no-support group (P<0.01). The late prophylactic rhG-CSF schedule was therefore more effective in countering neutropenia than either the early prophylactic or therapeutic schedule.

Aged↗
PubMed1996

Adrenomedullin stimulates calcium efflux from adrenal chromaffin cells in culture: possible involvement of an Na+/Ca2+ exchange mechanism.

The effect of adrenomedullin, a hypotensive peptide, on Ca2+ efflux from cultured bovine adrenal chromaffin cells was examined. Adrenomedullin stimulated the efflux of 45Ca2+ from the cells in a concentration-dependent manner (10(-7)M - 3x10(-6)M). Adrenomedullin did not increase the intracellular free Ca2+ ([Ca2+]i) level and catecholamine secretion. The adrenomedullin-stimulated 45Ca2+ efflux was not inhibited by incubation with Ca2+-free medium, but was inhibited by incubation with Na+-free medium. These results indicate that adrenomedullin stimulates extracellular Na+-dependent 45Ca2+ efflux from cultured bovine adrenal chromaffin cells, probably through its stimulatory effect on membrane Na+/Ca2+ exchange.

Adrenal Medulla↗
PubMed1996

Effect of extracellular adenosine 5'-triphosphate on Ca2+ efflux from freshly isolated adult rat cardiomyocytes.

The effect of extracellular adenosine 5'-triphosphate (ATP) on Ca2+ efflux from freshly isolated adult rat cardiomyocytes was examined. ATP stimulated the efflux of 45Ca2+ from the cells in a concentration-dependent manner (0.01-1 mM). The 45Ca2+ efflux from the cells was also stimulated by adenosine-5'-O-(3-thiotriphosphate)(ATP-gammas) and alpha,beta-methylene-ATP and adenosine 5'-diphosphate, but not by adenosine 5'-monophosphate and adenosine. The ATP-stimulated 45Ca2+ efflux was not affected by deprivation of the extracellular Ca2+, but was dependent on the presence of extracellular Na+. These results indicate that ATP stimulates extracellular Na+-dependent 45Ca2+ efflux from freshly isolated adult rat cardiomyocytes, probably through its stimulatory effect on the plasma membrane P2 purinoceptors which may couple to Na+/Ca2+ exchange.

Adenosine↗
PubMed1996

Physiological significance of plasma sulfoconjugated dopamine in patients with hypertension--clinical and experimental studies.

Sulfoconjugated catecholamines, especially dopamine sulfate, have recently attracted much attention because of the possibility of their conversion to active free dopamine by tissue arylsulfatase. In the present study, we have measured the plasma levels of free and sulfoconjugated dopamine in patients with hypertension and have investigated the physiological significance of sulfoconjugation. Results showed that the plasma level of dopamine sulfate in patients with essential hypertension was higher than the level in control subjects, and was highest in patients with renal hypertension. However, the plasma level of free dopamine showed no significant difference between patients with hypertension and normal subjects. Moreover, after normalization of blood pressure in hypertensive patients with medication, the plasma levels of conjugated dopamine decreased to almost the control value. In the experimental study, dopamine sulfate inhibited angiotensin II-induced aldosterone release from bovine adrenal cortical cells to a similar extent as produced by free dopamine. From these results, we have concluded that plasma sulfoconjugated dopamine may regulate free dopamine in the plasma of patients with hypertension, and it may have some physiological effects on blood pressure regulation.

Adrenal Cortex↗
PubMed1996

Significance of interstitial bone ingrowth under load-bearing conditions: a comparison between solid and porous implant materials.

Interstitial bone ingrowth is extremely important for optimum fixation of implanted materials under load-bearing conditions. In this study, three types of biomaterial test piece were manufactured in solid and open-pore structures, and implanted into dog femoral condyles. Bone formation and remodelling were observed histologically and roentgenologically for 24 weeks thereafter. The study demonstrated that, 24 weeks after implantation, thick fibrous tissue surrounded by corticalized bone formed around both solid smooth-surfaced alumina and titanium implants. On the other hand, however, with an implant made of an artificial osteochondral composite material, thickening of ingrown trabeculae could be observed as early as 4 weeks. Bone ingrowth into the titanium fibre mesh was ambundant and increased with time after implantation. This interstitial bone ingrowth resulted in the complete integration of this implant and the viable host bone. Our findings suggest that interstitial bone ingrowth has great significance, even though new bone formation and remodelling follows Wolff's law after the completion of the bonding between the bone and implanted material under load-bearing conditions. The artificial osteochondral composite material could lead to complete integration of the implant and viable bone, suggesting that it is a promising material for joint replacements. Moreover, the tibial joint surface which bore against the polyvinyl alcohol hydrogel surface of this implant remained intact, which suggests that this composite is a very promising biomaterial for use in joint prostheses.

Animals↗
PubMed1996

In vitro and in vivo analysis of human leukocyte binding by the antitumor polysaccharide, lentinan.

Lentinan (LNT), a (1-->3)-beta-D-glucan with (1--6)-beta-D-glucopyranoside branches, has marked antitumor effects in syngeneic and autochtonous hosts. Clinically, LNT has proved effective with chemotherapeutic agents in patients with recurrent gastric and colorectal cancer. However, the mechanism that triggers subsequent immunologic reactions remains obscure. We hypothesized that LNT must first bind to the host cells. Accordingly, we analyzed LNT binding to host cells in healthy volunteers after incubating their cells under a variety of conditions as well as intravenously injecting LNT then subjecting them to flow cytometry and immunofluorescent staining using monoclonal antibody (anti-LNT mAb). LNT bound to monocytes and neutrophils, but not to lymphocytes in vitro. The most avid LNT binding was to monocytes. The percentage of LNT-bound monocytes after 60 min incubation at 4 degrees C was greater than that at 37 degrees C. The binding of LNT to monocytes was inhibited slightly by anti-iC3b receptor (anti-CR3) mAb, strongly by anti-C3b receptor (anti-CR1) mAb, and completely by anti-CR1 and anti-CR3 mAb together. The percentages of LNT-binding monocytes in the peripheral blood increased significantly 3 and 4 after 2 mg LNT-injection and returned to low levels 5 h later. However, no increase in LNT-binding neutrophils and lymphocytes was observed. We concluded that binding of LNT to human monocytes may initiate the influence of this compound on the immune system and differ between individuals. Its binding site may be similar to the C3b receptor.

Adult↗
PubMed1996

Two effects of lysophosphatidic acid on Ca(2+)-movement in cultured bovine adrenal chromaffin cells.

We found that lysophosphatidic acid (LPA) exerted two effects on Ca(2+)-movement in cultured bovine adrenal chromaffin cells. At concentrations of above 10(-5) M, it induced slight, but significant 45Ca2+ influx, resulting in release of a small portion of stored catecholamine. At high concentrations it also significantly increased the intracellular Ca2+ concentration in Fura-2-loaded cells. At concentrations as low as 10(-7) M, it stimulated extracellular Na(+)-dependent 45Ca2+ efflux, possibly by increasing Na+/Ca2+ exchange. The maximal efflux of Ca2+ attained with 10(-5) M LPA was inhibited by tyrosine kinase inhibitors, but augmented by a protein kinase C inhibitor. These results suggest that LPA-induced Ca2+ efflux is controlled positively and negatively by mechanisms involving tyrosine kinase and protein kinase C, respectively.

Animals↗
PubMed1996

Firing characteristics of neurones in the superior colliculus and the pontomedullary reticular formation during orienting in unrestrained cats.

Cats were trained to fixate a center LED or light spot for 1-10 s and to orient to a target (LED or light spot), which appeared simultaneous with the disappearance of the fixation light. Firing characteristics of neurones in the superior colliculus (SC) and the pontomedullary reticular formation were examined systematically in cats performing the above orienting task. In the head-free condition, a majority of the superficial neurones in the SC was activated when a target appeared in a particular area in the visual field (receptive field) as in head fixed animals. We identified a new group of neurones in superficial layers of the SC, superficial fixation neurones, which fired tonically when fixated on a target light with little activity at fixating a center fixation light. In the intermediate and deep layers of the SC, many neurones fired when directed to a particular area in the visual field (movement field). In addition to these neurones, we found new groups of neurones fired tonically in a particular phase of orienting. These neurones were divided into three principal types, target activated, target suppressed and center fixation activated neurones. Target activated neurones fired tonically during the fixation of a target, but not during fixation of a center spot. Target suppressed neurones were characterized by a pause during fixation of targets irrespective of their location. They had clear phasic and tonic components. The phasic component was characterized by a movement field resembling that seen in a typical intermediate layer neurone. Center fixation activated neurones discharged during fixation of the center spot and exhibited suppression during fixation of the target. Many neurones in the pontomedullary reticular formation fired during orienting. Four major types of neurones, phasic, phasic sustained, pause and tonic neurones, were differentiated on the basis of their firing patterns. Phasic units were characterized by brief phasic firing during orienting and could be divided into four subtypes. Long lead phasic neurones began to fire 50-100 ms prior to the onset of a gaze shift and stopped well before the end of the gaze shift and the total number of firing was best correlated with the total angle of head rotation. Short lead phasic neurones started to fire 10-20 ms prior to a gaze shift and were further subdivided into decrement and plateau types. The decrement type exhibited a brief burst just prior to gaze shift and stopped discharging prior to the end of the gaze shift, while the plateau type fired tonically during the gaze shift and stopped firing after the gaze shift. Total number of discharges of both type was related to maximal angular velocity. The fourth type, gaze neurone, began firing coincident with the onset of the gaze shift and stopped firing at the completion of the gaze shift and the total number of discharges was closely related to total angle of head rotation Phasic sustained (PS) neurones fired 50-100 ms before the onset of a gaze shift and their discharges continued after the end of the gaze shift and were divided into three subtypes: augmenting, pause and plateau. The augmenting type was characterized by a transient increase of firing during the gaze shift and a maintained slow rate of firing following the gaze shift. Total number of discharges related to head movement amplitude and the sustained activity was correlated with head position. The pause type was suppressed during the gaze shift and was tonically active during a head movement. The plateau type had a weak phasic component and discharged at a fairly constant rate. The pause and plateau types appeared to be related to head amplitude and head position, respectively. Tonic units were classified into several types. Target fixation neurones exhibited sustained firing when the cat was fixating a target, irrespective of its location, but did not show sustained firing when the animal fixated the fixation light. Fixation neurones fired tonical

Animals↗
PubMed1996

Multiple pleomorphic adenomas arising in the parotid and submandibular lymph nodes.

We report rare case of multiple pleomorphic adenomas arising in the parotid and submandibular lymph nodes of a 21-year-old man. These tumours were surrounded by lymphoid tissue which was almost identical to that of the cortex of lymph node. The possibility of metastasizing pleomorphic adenomas was discounted because the mitotic activity was low and there were no signs of infiltration. Heterotopic salivary gland tissue was also found in the lymph nodes that contained the tumours, and each tumour expressed a similar immunohistochemical staining pattern to that of the salivary gland tissue. These findings indicate that these pleomorphic adenomas probably arose from the salivary gland tissue within the lymph nodes.

Adenoma, Pleomorphic↗
PubMed1996

Infective endocarditis caused by Campylobacter fetus after allogeneic tooth transplantation: a case report.

A patient developed infective endocarditis caused by Campylobacter fetus. He gave a history of recent dental extraction and allogeneic tooth transplantation. He was treated with various antibodies to which the organism was said to be sensitive, but it was not until the transplanted tooth was removed that he started to improve. The mode of infection was thought to be blood borne through the open tooth socket from the raw chicken that he ate regularly.

Animals↗