Biomedical subjects

H Yamada

Publications and source records attributed to H Yamada.

At least 145 records · Page 8Linked to original sources

PubMed2001

Role of the conserved Ser-Tyr-Lys triad of the SDR family in sepiapterin reductase.

Sepiapterin reductase (EC 1.1.1.153; SPR) is an enzyme involved in the biosynthesis of tetrahydrobiopterin; and SPR has been identified as a member of the NADP(H)-preferring short-chain dehydrogenase/reductase (SDR) family based on its catalytic properties for exogenous carbonyl compounds and molecular structure. To examine possible differences in the catalytic sites of SPR for exogenous carbonyl compounds and the native pteridine substrates, we investigated by site-directed mutagenesis the role of the highly conserved Ser-Tyr-Lys triad (Ser and YXXXK motif) in SPR, which was shown to be the catalytic site of SDR-family enzymes. From the analysis of catalytic constants for single- and double-point mutants against the triad, Ser and YXXXK motif, in the SPR molecule, participate in the reduction of the carbonyl group of both pteridine and exogenous carbonyl compounds. The Ser and the Tyr of the triad may co-act in proton transfer and stabilization for the carbonyl group of substrates, as was demonstrated for those in the SDR family. But either the Tyr or the Ser of SPR can function alone for proton transfer to a certain extent and show low activity for both substrates.

Alcohol Oxidoreductases↗

PubMed2001

Upregulation of immunoreactive angiotensin II release and angiotensinogen mRNA expression by high-frequency preganglionic stimulation at the canine cardiac sympathetic ganglia.

The possible involvement of the local angiotensin system in ganglionic functions was investigated in the canine cardiac sympathetic ganglia. Positive chronotropic responses to preganglionic stellate stimulation at high frequencies, after intravenous administration of pentolinium plus atropine, were inhibited by the nonpeptide angiotensin AT(1) receptor antagonist forasartan or the angiotensin I-converting enzyme inhibitor captopril, whereas the rate increases elicited by the postganglionic stellate stimulation and norepinephrine given intravenously failed to be inhibited by these antagonists. The levels of endogenous immunoreactive angiotensin II, as determined by radioimmunoassay in the incubation medium of the stellate and inferior cervical ganglia, were increased after the high-frequency preganglionic stimulation of the isolated ganglia. The increment of the peptide was also antagonized by the pretreatment with captopril but not by a chymase inhibitor, chymostatin. The expression of angiotensinogen mRNA was observed in the stellate ganglion, adrenal, liver, and lung but not in the ovary and spleen. The expression of the mRNA in the stellate and inferior cervical ganglia increased after high-frequency preganglionic stimulation of the in vivo dogs for a period of 1 hour. These results indicate that an intrinsic angiotensin I-converting enzyme-dependent angiotensin system exists in the cardiac sympathetic ganglia, which is activated by high-frequency preganglionic stimulation.

Angiotensin II↗

PubMed2001

Numerical study of Lyapunov exponents for products of correlated random matrices.

We numerically study Lyapunov spectra and the maximal Lyapunov exponent (MLE) in products of real symplectic correlated random matrices, each of which is generated by a modified Bernoulli map. We can systematically investigate the influence of the correlation on the Lyapunov exponents because the statistical properties of the sequence generated by the map, whose correlation function shows power-law decay, have been well investigated. It is shown that the form of the scaled Lyapunov spectra does not change much even if the correlation of the sequence increases in the stationary region, and in the nonstationary region the forms are quite different from those obtained in the delta-correlated purely random case. The fluctuation strength dependence of the MLE changes with increasing correlation, and a different scaling law from that of the delta-correlated case can be observed in the nonstationary region. Moreover, the statistical properties of the probability distribution of the local Lyapunov exponents are quite different from those obtained from delta-correlated random matrices. Slower convergence that does not obey the central-limit theorem is observed for increasing correlation.

Journal Article↗

PubMed2001

High-pressure NMR study of cis-1,n-disubstituted[n]paracyclophanes. Effect of increased pressure on the hindered internal rotation.

The effect of hydrostatic pressure on the rate of internal rotation of title compounds has been examined by the DNMR method. Quartz pressure-resisting NMR cells were used to realize the high-pressure experiments up to 390 (line shape measurements) and 450 MPa (chemical shift measurements). Application of hydrostatic pressure was found to accelerate the rotation of the benzene ring, while pressure-induced low-frequency chemical shifts of bridge methylene protons indicated that there is a considerable shrinkage of the methylene bridge structure upon pressurization.

Journal Article↗

PubMed2001

Successful priming and tolerization of T cells to orally administered antigens in B-cell-deficient mice.

B cells have been shown to function as APCs capable of inducing both T cell priming and tolerization. Recently, B cells were also revealed to be essential in the organogenesis of Payer's patches (PPs), which have been supposed to play an important role in the initiation of mucosal immune responses. In this study, we examined the roles of B cells in T cell response to orally administrated antigen using B-cell-deficient mice. It was revealed that (1) both a single high dose and repeated low doses of orally administered OVA successfully induced tolerance of T cells in B-cell-deficient mice and (2) oral administration of OVA with cholera toxin successfully primed T cells in B-cell-deficient mice. Thus, it was revealed that B cells are not required for both priming and tolerization of T cells to orally administered antigens. These results also contradict the supposed roles of PPs in mucosal immune responses.

Adjuvants, Immunologic↗

PubMed2001

Light-harvesting and photocurrent generation by gold electrodes modified with mixed self-assembled monolayers of boron-dipyrrin and ferrocene-porphyrin-fullerene triad.

Three different kinds of mixed self-assembled monolayers have been prepared to mimic photosynthetic energy and electron transfer on a gold surface. Pyrene and boron-dipyrrin were chosen as a light-harvesting model. The mixed self-assembled monolayers of pyrene (or boron-dipyrrin) and porphyrin (energy acceptor model) reveal photoinduced singlet-singlet energy transfer from the pyrene (or boron-dipyrrin) to the porphyrin on the gold surface. The boron-dipyrrin has also been combined with a reaction center model, ferrocene-porphyrin-fullerene triad, to construct integrated artificial photosynthetic assemblies on a gold electrode using mixed monolayers of the respective self-assembled unit. The mixed self-assembled monolayers on the gold electrode have established a cascade of photoinduced energy transfer and multistep electron transfer, leading to the production of photocurrent output with the highest quantum yield (50 +/- 8%, based on the adsorbed photons) ever reported for photocurrent generation at monolayer-modified metal electrodes and across artificial membranes using donor-acceptor linked molecules. The incident photon-to-current efficiency (IPCE) of the photoelectrochemical cell at 510 and 430 nm was determined as 0.6% and 1.6%, respectively. Thus, the present system provides the first example of an artificial photosynthetic system, which not only mimics light-harvesting and charge separation processes in photosynthesis but also acts as an efficient light-to-current converter in molecular devices.

Journal Article↗

PubMed2001

Laparoscopic Heller myotomy and Dor fundoplication for achalasia: analysis of successes and failures.

BACKGROUND: In the treatment of achalasia, surgery has been traditionally reserved for patients with residual dysphagia after pneumatic dilatation. The results of laparoscopic Heller myotomy have proven to be so good, however, that most experts now consider surgery the primary treatment. HYPOTHESIS: The outcome of laparoscopic myotomy and fundoplication for achalasia is dictated by technical factors. SETTING: University hospital tertiary care center. DESIGN: Retrospective study. PATIENTS AND METHODS: One hundred two patients with esophageal achalasia underwent laparoscopic Heller myotomy and Dor fundoplication. Fifty-seven patients had been previously treated by pneumatic dilatation or botulinum toxin. The design of the operation involved a 7-cm myotomy, which extended 1.5 cm onto the gastric wall, and a Dor fundoplication. Esophagrams, esophageal manometric findings, and video records of the procedure were analyzed to determine the technical factors that contributed to the clinical success or failure of the operation. MAIN OUTCOME MEASURE: Swallowing status. RESULTS: In 91 (89%) of the 102 patients, good or excellent results were obtained after the first operation. A second operation was performed in 5 patients to either lengthen the myotomy (3 patients) or take down the fundoplication (2 patients). Dysphagia resolved in 4 of these patients. The remaining 6 patients were treated by pneumatic dilatation, but dysphagia improved in only 1. At the conclusion of treatment, excellent or good results had been obtained in 96 (94%) of the 102 patients. CONCLUSIONS: These data show that a Heller myotomy was unsuccessful in patients with an esophageal stricture; a short myotomy and a constricting Dor fundoplication were the avoidable causes of residual dysphagia; a second operation, but not pneumatic dilatation, was able to correct most failures; and that the identified technical flaws were eliminated from the last half of the patients in the series.

Adolescent↗

PubMed2001

Prenatal diagnosis of agnathia-holoprosencephaly: three-dimensional imaging by helical computed tomography.

We report a case of agnathia-holoprosencephaly which was prenatally diagnosed based on helical computed tomography (CT) images obtained at 23 weeks of gestation. Ultrasound examination first showed the presence of alobar holoprosencephaly, but the facial structures were not clearly detailed. However, three-dimensional imaging by helical CT precisely demonstrated the most striking feature of agnathia: absence of the mandible. This technique provided us valuable information that contributed to the in utero diagnosis. In utero helical CT is a useful examination tool for the diagnosis of osteogenic abnormalities.

Adult↗

PubMed2001

Stereoselectivity of the folate transporter in rabbit small intestine: studies with amethopterin enantiomers.

Stereoselectivity of the folate transporter was examined using rabbit intestinal brush border membrane vesicles (BBMV). Methotrexate (MTX) and the antipode (D-amethopterin) were used as model substrates of the transporter. Folic acid (FA) and MTX were actively taken up into BBMV in the presence of an H+ gradient. Initial uptake of FA and MTX was concentration-dependent with Km values of 1.5 and 1.6 microM for FA and MTX, respectively. FA and MTX mutually inhibited uptake in a competitive manner, with Ki values being similar to the corresponding Km values, demonstrating that FA and MTX share the folate transporter. D-Amethopterin also inhibited FA uptake competitively, with a Ki value approximately 60-fold greater than that of MTX, showing that the affinity of the D-isomer (D-amethopterin) to the folate transporter is much less than that of the L-isomer (MTX). The extent of stereoselectivity observed in the present study is consistent with the previously reported differences in plasma concentration between amethopterin enantiomers following oral administration in humans.

Animals↗

PubMed2001

Reevaluation of the origin of CD44(high) "memory phenotype" CD8 T cells: comparison between memory CD8 T cells and thymus-independent CD8 T cells.

CD44(high)CD8 T cells in naive mice, which increase with age, and are often referred to as memory CD8 T cells. However, since thymus-independent CD8 T cells have also been shown to be CD44(high), the origin of the CD44(high)CD8 T cells in naive mice remains unclear. In this study, we compared the characteristics of memory CD8 T cells and thymus-independent CD8 T cells in TCR transgenic mice to clarify the origin of the CD44(high)CD8 T cells in naive normal mice. The memory and thymus-independent CD8 T cells showed differences in surface molecules, spontaneous cell death, cytokine production, and response to IL-2R binding of cytokines. Importantly, the "memory phenotype" CD8 T cells in naive normal mice showed similar characteristics to the thymus-independent CD8 T cells, but differed greatly from "true" memory CD8 T cells in the TCR transgenic mice. Therefore, we conclude that a significant part of the CD44(high) memory phenotype CD8 T cells in naive normal mice represents thymus-independent CD8 T cells, which may participate in age-related changes in immune responses.

Animals↗

PubMed2001

Determination of S-[2-carboxy-1-(1H-imidazol-4-yl)ethyl]glutathione, a novel metabolite of L-histidine, in tissue extracts from sunlight-irradiated rat by capillary electrophoresis.

Exposure of the skin to sunlight results in an increase in the content of epidermal urocanic acid, a key metabolite of L-histidine, and some portions of the metabolite penetrate into the body fluid. S-[2-Carboxy-1-(1H-imidazol-4-yl)ethyl]glutathione (GS(CIE)), an adduct of glutathione and urocanic acid, was proposed to be an origin of a urinary compound, S-[2-carboxy-1-(1 H-imidazol-4-yl)ethyl]-L-cysteine (Cys(CIE)). Various catabolites of Cys(CIE) were also isolated from human urine previously. However, no direct evidence to show the existence of GS(CIE) as a biological material had been found. By using capillary electrophoresis, the glutathione adduct has now been found in the extracts of rat tissues from the kidney, liver, skin and blood when the rat was kept under conditions of sunlight irradiation after the fur on the dorsal skin had been clipped. On the other hand, no or a trace of GS(CIE) was determined in rat tissue extracts when the animal was kept indoor in usual manner. The glutathione adduct was isolated from the kidney extract of the sunlight-irradiated rat using ion-exchangers and high-voltage paper electrophoresis, and determined by fast-atom-bombardment mass spectrometry. These results indicate that GS(CIE) formation actually occurs in the body and that the formation is accelerated by exposing the rat to sunlight irradiation. From these findings, we propose an alternative pathway of histidine metabolism which is initiated by the adduction of urocanic acid to glutathione to form GS(CIE) and terminates with the formation of the urinary compounds via Cys(CIE).

Animals↗

PubMed2001

Time course of arterial hyperintensity with fast fluid-attenuated inversion-recovery imaging in acute and subacute middle cerebral arterial infarction.

The purpose of this study was to evaluate the time course of arterial hyperintensity (AH) in acute and subacute cerebral infarctions of the middle cerebral artery (MCA) distribution by using fast fluid-attenuated inversion-recovery (FLAIR) imaging. A total of 40 FLAIR MR examinations were performed in 27 patients with MCA infarction within 13 days after ictus. Thirteen patients underwent two MR examinations during this period. Thrombotic or embolic infarctions were included in this study, but lacunar infarctions were excluded. The presence or absence of AH and the location of AH were analyzed. Overall, AH was found in 24 (60%) of 40 FLAIR examinations within 13 days after onset. AH was seen in 17 (100%) examinations less than 24 hours old, four (40%) of 10 examinations 1-4 days old, two (18%) of 11 examinations 5-9 days old, and one (50%) of two examinations 10-13 days old. AH was most frequently found at the sylvian fissure (87%), followed by the sulci (54%), and the horizontal segment of MCA (29%) in the affected MCA distribution. Although AH could be seen even at 13 days after ictus, the presence of AH declined over time. AH represented an early sign of acute embolic or thrombotic infarction. J. Magn. Reson. Imaging 2001;13:987-990.

Aged↗

PubMed2001

Hydratases involved in nitrile conversion: screening, characterization and application.

The discovery of new enzymes with greater activity and specificity opens new, simple routes for synthetic processes, and consequently, new methods to solve environmental problems. A number of nitrile-related enzymes have been screened over the past few years for use in developing synthetic applications. Microbial nitrile hydratase (NHase) has great potential as a catalyst in organic chemical processing because the enzyme can convert nitriles to the corresponding higher value amides under mild conditions, and has now been applied to the industrial productions of acrylamide and nicotinamide. Particularly, the former production is the first successful example of a bioconversion process for the manufacture of a commodity chemical. The characterization of the enzyme at the molecular level has provided new insights into how the molecular structure determines the enzyme function, and how the regulatory system controls the expression of the enzyme genes to improve the enzyme and the NHase-dependent process.

Acrylamide↗

PubMed2001

Occult lymph node metastases detected by cytokeratin immunohistochemistry predict recurrence in node-negative endometrial cancer.

OBJECTIVE: Even after curative resection of early endometrial cancer, some patients die as a result of recurrence. We believe that these patients likely had occult lymph node metastases at the time of diagnosis. In an attempt to identify the responsible occult metastases, the clinicopathological significance of cytokeratin expression in lymph nodes with unconfirmed metastasis was evaluated retrospectively in patients with endometrial carcinoma. METHODS: We examined 304 pelvic lymph nodes and 46 primary tumors excised from 46 patients with endometrial cancer, including 36 with Stage I disease and 10 with Stage IIIc disease. Formalin-fixed paraffin-embedded tissue sections were stained immunohistochemically using antibodies against cytokeratin, CA125, and macrophage-related antigen. Sections were also stained with hematoxylin and eosin. RESULTS: In 10 patients with Stage IIIc disease, cytokeratin expression was detected in cells other than the tumor cells in all 13 lymph nodes with metastasis and also in 20 (30.3%) of 66 lymph nodes without metastasis. Cytokeratin expression was observed in 37 (16.4%) of 225 lymph nodes with unconfirmed metastasis, which were obtained from 14 of 36 patients with Stage I disease. Five of fourteen patients with lymph nodes expressing cytokeratin had recurrent disease in the pelvic cavity, while all 22 patients with unconfirmed cytokeratin expression in their lymph nodes showed no recurrence. Cytokeratin and CA125 were detected simultaneously on macrophages in lymph nodes. Cytokeratin expression in lymph nodes was closely related to lymph-vascular space involvement of the primary tumor, but was not related to either histological grade or depth of myometrial invasion. Multivariate analysis identified cytokeratin expression as an independent risk factor for recurrence in Stage I endometrial cancer. CONCLUSIONS: The immunohistochemical expression of cytokeratin in lymph nodes with undetected metastases predicts occult metastasis to these nodes and is a risk factor for recurrence in early-stage endometrial cancer.

CA-125 Antigen↗

PubMed2001

Dominant-negative mutation of p53 tumor suppressor gene in endometrial carcinoma.

BACKGROUND: It has been suggested that mutation of the TP53 tumor suppressor gene is involved in endometrial carcinogenesis. However, the status of p53 function in endometrial cancers has not yet been investigated in detail. METHODS: We surveyed inactivating p53 mutations in endometrial carcinomas using the yeast p53 functional assay, which can evaluate the transcriptional activity of p53 in vivo in yeast. To the detected p53 mutants, we also applied a transdominance assay, which assesses the dominant-negative property of mutants. RESULTS: Of 23 endometrial carcinomas, 9 tumors (39.1%) were found to harbor p53 mutations. Only 1 of the 6 mutants in 18 endometrioid-type tumors showed dominant-negative capacity. In contrast to the endometrioid-type tumor, all 3 mutations in 5 serous-type tumors (R273H, 9-bp deletion in codons 240-243, and R248W) showed dominant-negative capacity and presented in a homozygous state in the tumors, indicating a complete functional inactivation. CONCLUSIONS: Although this study included a relatively small number of cases and therefore is a preliminary study, these results suggest that the dominant-negative mutation of the TP53 gene is related to serous adenocarcinoma. The role of the dominant-negative status of p53 mutants in endometrial carcinogenesis and progression of this disease should be further investigated.

Adult↗

PubMed2001

Glucocorticoid-regulated expression of exogenous human growth hormone gene in rats.

The aim of this study was to control in vitro and in vivo expression of the growth hormone (GH) gene using a glucocorticoid-sensitive promoter, the mouse mammary tumor virus long terminal repeat (MMTV LTR). We inserted the cDNA encoding the 20-kDa form of human GH (20K-GH) downstream of the MMTV LTR of plasmid pMSG, and used lipofection to transfer it to 3Y1 cells together with plasmid pMX, which contains a puromycin-resistant element. The secretion of GH from the selected transformants was dose-dependently augmented by the application of hydrocortisone, corticosterone, or dexamethasone, among which dexamethasone was the most potent. Analysis of the time course showed that 20K-GH secretion began to increase within 2 hours after the addition of glucocorticoid and reached a maximal level of about threefold over the unstimulated control at 3 hours; secretion then gradually declined and returned to near basal levels at 19 hours. Repeated glucocorticoid application led to repeated increases in GH secretion. When GH-producing cells were microcapsulated and transplanted into the abdominal cavities of rats, 20K-GH was detected in the plasma under control conditions and increased about 3.3-fold after administration of dexamethasone. We suggest that GH expression driven by the MMTV LTR promoter may be under the control of an endogenous glucocorticoid in vivo.

Animals↗

PubMed2001

Analysis of predictive factors for recurrence after hepatectomy for colorectal liver metastases.

Hepatectomy for liver metastases from colorectal cancer has recently received general acceptance as a safe, potentially curative treatment. Most patients, however, die of recurrent disease after hepatectomy. The predictive factors for recurrence after first resection of liver metastases have not yet been clarified. The authors aimed to determine the factors that can predict recurrence, especially hepatic-only recurrence after hepatectomy for colorectal liver metastases. Seventy-six patients who underwent liver resection of colorectal metastases were studied retrospectively. Forty-seven (61.8%) of the patients had a recurrence. The patients' disease-free survival after first hepatectomy and the second recurrence sites were univariately and multivariately analyzed using 16 clinicopathologic variables. Wall invasion, lymph node metastases, lymphatic invasion, venous invasion of the primary tumor, 24 months or longer disease-free interval after resection of the primary colorectal cancer, and bilateral liver metastases significantly influenced the disease-free survival (log-rank test: p < 0.05). The multivariate analysis revealed that venous invasion of the primary tumor and bilateral hepatic metastases were independent risk factors for recurrence after hepatectomy. The liver was the only site of second recurrence in 23 patients. Patients with lymph node metastases and venous invasion of the primary tumor had a significant difference between hepatic-only and extrahepatic recurrence after first hepatectomy (chi-square test or Fishers' exact test: p < 0.05). Recurrence after hepatectomy was influenced more by factors associated with the primary colorectal cancer than factors surrounding the first liver metastases. Venous invasion of the primary colorectal cancer was the most important predictable factor for hepatic-only second recurrence.

Adult↗

PubMed2001

Neck muscle responses to abrupt vertical acceleration in the seated human.

The control of neck muscle during marked changes in "g" loading must be to protect head-trunk orientation. However, little is known about the organization of reflexes. We therefore investigated the shortest latency in neck muscle evoked by abrupt ascending and descending vertical acceleration with a stroke of 20 cm and peak acceleration 0.4xg in six healthy subjects. The subjects were seated upright and restrained on a chair driven by a hydraulic servo system. Ascent induced small responses in sternocleidomastoid muscles (SCMs) with a latency of 24.0 ms (SE 1.7) from onset of head acceleration, followed by larger responses of 100 ms in duration. In comparison the responses in SCMs evoked by descent were significantly delayed, with greater interindividual variations at 44.1 ms (SE 3.1) and smaller in amplitude than responses in ascent. Latencies were consistent and showed no habituation. In order to eliminate stretch components, we measured the neck responses to vertical acceleration with the head fixed by cervical collar. The latency of the fast response of SCM evoked by ascent was not significantly different from the latency of SCMs without the collar. These results may indicate that the fast responses of SCMs to sudden ascent may be composed of a vestibular-collic reflex for making the neck and head rigid for defense to sudden gravitational change.

Acceleration↗