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Biomedical subjects

R Okumura

Publications and source records attributed to R Okumura.

At least 19 recordsLinked to original sources
PubMed2000

Interplay between efflux pumps may provide either additive or multiplicative effects on drug resistance.

The effects of simultaneous expression of several efflux pumps on antibiotic resistance were investigated in Escherichia coli and Pseudomonas aeruginosa. Several combinations of efflux pumps have been studied: (i) simultaneous expression of a single-component efflux pump, which exports antibiotics into the periplasm, in combination with a multicomponent efflux pump that accomplishes efflux directly into the external medium; (ii) simultaneous expression of two single-component pumps; and (iii) simultaneous expression of two multicomponent pumps. It was found that when efflux pumps of different structural types were combined in the same cell (the first case), the observed antibiotic resistance was much higher than that conferred by each of the pumps expressed singly. Simultaneous expression of pairs of single-component or multicomponent efflux pumps (the second and third cases) did not produce strong increases in antibiotic resistance.

Anti-Bacterial Agents↗
PubMed2000

Prolapsing gyrus rectus as a cause of progressive optic neuropathy.

The pathogenesis of optic neuropathy caused by neurovascular compression or by similar mechanisms is unclear. Thin-slice magnetic resonance (MR) imaging was performed in 69 patients with optic neuropathy without demonstrable ophthalmological lesions (57.0 +/- 17.1 years of age) and 102 normal subjects (57.7 +/- 13.9 years of age). The MR imaging features were classified into "no compression" by the internal carotid artery (ICA), "compression" by the ICA, "no contact" with the anterior cerebral artery (ACA) or the gyrus rectus, "contact" with either or both, "compression" by the ACA, and "compression" by the gyrus rectus. The Spearman correlation coefficients were calculated between patients or controls, the MR classification, and the age, and the number of patients in each MR classification were evaluated by the chi 2 test. Five of the 69 patients with rapidly progressive symptoms were operated on via the frontotemporal approach. The MR imaging feature of "compression" by the gyrus rectus was the best predictor of optic neuropathy (Spearman correlation coefficients rho = -0.23646, p < 0.0018). This MR imaging feature was observed in 38 of 69 patients and in 32 of 102 controls (p = 0.002). Compression of the nerve by the gyrus rectus or the ACA was confirmed in all five operated cases. Decompression of the nerve was fully achieved in four of the five patients, and their symptoms have not progressed since then. Optic neuropathies due to compression by the prolapsing gyrus rectus are not well understood. Such neuropathies may be detected by MR imaging.

Adolescent↗
PubMed1999

Efficient coupled transcription/translation from PCR template by a hollow-fiber membrane bioreactor.

A novel bioreactor using a hollow-fiber membrane was developed for the coupled transcription/translation system using T7 RNA polymerase and Escherichia coli S30 extract. The large surface area per the reaction volume of the reactor assured rapid mass transfers of substrates into the reaction mixture and of wastes out from it across the membrane by their molecular diffusion. The flux was large enough to maintain nucleotide concentrations for more than 3 h, which increased the protein synthesis greatly. In addition, the T7 terminator sequence downstream from the reporter genes was found to increase the synthesized protein significantly, especially when the product of polymerase chain reaction (PCR) was used as a template. Implementation of this finding and use of the bioreactor developed multiplied the productivity of protein by the in vitro direct expression from PCR template.

Base Sequence↗
PubMed1999

Isolation and transcriptional analysis of a cellulase gene (cell) from the basidiomycete Irpex lacteus.

A gene (named cell) homologous to the cellobiohydrolase I gene (cbhl) of Trichoderma reesei was isolated and sequenced from the white rot basidiomycete Irpex lacteus MC-2. The cell open reading frame consists of 1551 bp, which is interrupted by two introns, encoding a polypeptide of 517 amino acid residues with a calculated molecular mass of 54,522 Da. The deduced amino acid sequence showed that CEL1 (the protein encoded by cell) has a modular structure consisting of a catalytic domain of 449 amino acids and a C-terminal cellulose-binding domain (CBD) of 36 amino acids separated by a proline-, serine-, threonine-rich linker region of 32 amino acids. The CEL1 catalytic domain is homologous with fungal cellobiohydrolases (CBHs) belonging to family 7 of the glycosyl hydrolases. The transcription of cell was induced in the presence of various cellulosic substrates and repressed by glucose. It was therefore concluded that the reported sequence represents the first cellulase gene isolated from the basidiomycete Irpex.

Journal Article↗
PubMed1998

Mass and mass distribution of below-knee prostheses: effect on gait efficacy and self-selected walking speed.

OBJECTIVE: To study mass and mass distribution effect on function of below-knee prostheses. DESIGN: Design modifications were done to produce proximal center of mass location versus distal center of mass location variations, and prosthesis weight was modified from 42% to 70% of normal limb weight. Work across joints of affected and unaffected extremities was compared to assess the ability of the prosthesis to substitute for function loss. SETTING: University biomechanics laboratory. PARTICIPANTS: Fifteen volunteers with below-knee amputations, residual limb length greater than 8.3 cm, but excluding Syme amputations. INTERVENTIONS: Patients walked with all configurations at self-selected walking speeds and 120 m/min. MAIN OUTCOME MEASURES: Self-selected walking speed and metabolic efficiency. Work across the joints of affected and unaffected sides was compared. RESULTS: Proximal center of mass location produced a more efficient gait. Weight change from 42% to 70% of normal had no significant effect. Mechanical studies show that the prosthesis is a relatively poor substitute for the normal limb; most work is done by the nonamputated side. Particularly, the prosthesis failed to produce effective forward impulses on the body, resulting from push-off and deceleration of the swing leg. CONCLUSIONS: For a proximal center of mass, lightweight distal components (e.g., feet) should be used; it is questionable whether further expenditure to develop ultralightweight prostheses would be cost effective for level walking.

Adolescent↗
PubMed1997

Culture in the presence of sugars increases activity of multi-drug efflux transporter on Haloferax volcanii.

We found that when a growth medium contained glucose, wild-type cells of Haloferax volcanii were able to grow even in the presence of doxorubicin (DOX), an anti-cancer reagent, whereas they usually cannot grow in its presence. The reason was that cells grown in the presence of glucose (glucose-grown cells) showed high multi-drug efflux activity even though the growth medium contained no DOX or substrates of the transporter. This transporter was ATP-driven and the elevation of efflux activity was not due to an increase in intracellular ATP contents. The activity was increased not only by glucose but also by sugars that could be metabolized.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1997

Interface pressures and shear stresses at thirteen socket sites on two persons with transtibial amputation.

Residual limb/prosthetic socket interface pressures and shear stresses were measured at 13 sites on two subjects with unilateral transtibial amputation (TTA) using total-contact patellar-tendon-bearing prostheses. Maximal interface stresses during stance phase for each of 13 transducer sites were determined, then means for all steps calculated. Maximal pressure and resultant shear stress during stance phase were shown at anterior distal or mid-limb sites and the maxima occurred during the first 50% of stance phase. Anterior medial and lateral proximal sites showed their greatest pressure during the second 50%. At lateral mid-limb and popliteal fossa sites, resultant shear stress directions suggest that soft tissue was displaced toward the socket brim during weight-bearing. Results also suggest that skin across the distal tibial crest was in tension at the times of the first and second peaks in the shank axial force-time curve in all sessions. Significant difference (p < 0.05) in maximal stresses between sessions conducted > 3 weeks apart were apparent for both subjects.

Adult↗
PubMed1993

Anterior pituitary gland in pregnancy: hyperintensity at MR.

The authors obtained midline sagittal T1-weighted magnetic resonance images of the pituitary gland in 30 female patients: five pregnant; two postpartum; and 23 nonpregnant, of childbearing age, and without evidence of pituitary gland disorder. In pregnant and postpartum patients, the relative signal intensity of the anterior lobe compared with the pons was statistically higher than that in the control group (P < .001). In the pregnant patients, positive correlation was noted between the signal intensity ratio of the anterior lobe and the pons and gestational age. The authors believe that the hyperintensity of the anterior pituitary lobe in pregnant and postpartum patients is a physiologic variation. Because the anterior lobe of an infant may also be hyperintense on T1-weighted images and because the anterior lobes of an infant and a pregnant woman are histologically similar, the mechanism responsible for the hyperintensity in each case may be the same. It is important to know that the anterior lobe may be hyperintense in pregnant or postpartum women, especially in cases of probable pituitary gland abnormality accompanying pregnancy, such as pituitary hemorrhage, Sheehan syndrome, or lymphocytic adenohypophysitis.

Adult↗
PubMed1992

Nuclear magnetic resonance abnormalities of the cerebral white matter in children with acute lymphoblastic leukemia and malignant lymphoma during and after central nervous system prophylactic treatment with intrathecal methotrexate.

BACKGROUND: A prospective study was conducted to test the feasibility of nuclear magnetic resonance (NMR) imaging in the early diagnosis of treatment-induced leukoencephalopathy. METHODS: The study group included 16 patients with acute lymphoblastic leukemia and 4 patients with malignant lymphoma. All were given intravenous and intrathecal (IT) methotrexate (MTX) for central nervous system prophylaxis. Serial NMR studies were performed before and/or during induction-consolidation cycles. RESULTS: NMR imaging disclosed leukoencephalopathy in 8 of the 20 patients (40%) in the early stages of treatment. In six of the eight, the leukoencephalopathy was resolved after temporary or permanent interruption of IT MTX, and chemotherapy was completed successfully. The other two patients are being treated. Transient neurologic abnormalities developed in two of the eight patients. CONCLUSIONS: The possible causal relationship between leukoencephalopathy and the antimetabolic effects of MTX is discussed. This study clearly shows that NMR imaging is valuable in the early diagnosis and management of treatment-induced leukoencephalopathy.

Adolescent↗
PubMed1992

Vasorelaxant effect of trapidil on human basilar artery.

We have investigated the vasorelaxant effect of trapidil on human isolated basilar artery. Trapidil (10(-5)-10(-4) M) dose-dependently caused relaxation in vascular strips with or without endothelium, with no significant difference between the two types of strips. The relaxation responses were not inhibited by atropine, propranolol or methylene blue. Trapidil increased the concentration of 6-keto-PGF1 alpha, a prostacyclin degradation product, released from an artery ring in the incubation medium, but trapidil-induced relaxation was not inhibited by indomethacin. Pretreatment of vascular strips with 10(-5) M trapidil increased the relaxation responses to forskolin and dibutyryladenosine cyclic monophosphate but not to sodium nitroprusside or 8-bromoguanosine cyclic monophosphate. Trapidil induced a significant increase in the cAMP concentration but not in the cGMP concentration in artery strips. These results suggest that the relaxation response to trapidil is not caused by prostacyclin release or an increase in cGMP in the smooth muscle, but possibly by an increase in the cAMP levels, probably via an inhibitory effect on cAMP phosphodiesterase.

6-Ketoprostaglandin F1 alpha↗
PubMed1991

Magnetic resonance imaging of neurohypophyseal germinomas.

The authors reviewed magnetic resonance (MR) images in seven cases of germinoma in the hypothalamoneurohypophyseal axis (HNA). The intrasellar portions were clearly identified in six germinomas. Two small germinomas of these six were located only in the neurohypophysis. The major parts of the four large germinomas were located below the optic chiasm, and the large intrasellar portions were demonstrated. The remaining one small germinoma was localized from the pituitary stalk to the third ventricular floor. These findings strongly suggest that the primary site of germinomas in the HNA is the neurohypophysis. In the four large germinomas, the tumor shape was similar to that of pituitary adenoma. The authors believe that age (limited to first three decades), symptoms (diabetes insipidus), MR findings (absence of normal hyperintense signal of the posterior pituitary on T1-weighted (T1WI) images, and homogeneous hypointensity to the pons on T1WI images/isointensity on T2-weighted images are important in differential diagnosis.

Adolescent↗
PubMed1989

Development and aging of brain midline structures: assessment with MR imaging.

The development and aging of four brain midline structures--the pituitary gland, pons, cerebellar vermis, and corpus callosum--were studied. The dimensions and area of these structures were measured by means of midsagittal magnetic resonance imaging. The study group consisted of 94 patients newborn to 15 years old and 49 patients and seven volunteers 16-60 years old. Except for growth spurts in the 1st year and in the 10-15-year age range, the pituitary gland showed linear growth. The pons, cerebellar vermis, and corpus callosum all showed exponential growth. The cerebellar vermis showed the sharpest 1st-year growth spurt, followed by the corpus callosum and the pons. The pituitary gland showed a decrease in size in the 51-60-year age range. The corpus callosum also showed a tendency to diminish in size but to a lesser degree. There were no statistically significant declines in the size of either the pons or the cerebellar vermis in the 51-60-year age range.

Adolescent↗
PubMed1983

[A double blind clinical trial of cefamandole and cefmetazole in complicated urinary tract infections].

We conducted a randomized double blind comparison of cefamandole (CMD) and cefmetazole (CMZ) in the treatment of 193 patients with complicated urinary tract infections. The patients received 1 gram of CMD or CMZ twice a day intravenously by drip infusion over 1 hour for 5 days. Pretreatment urinary leukocyte counts and urinary bacterial counts were at least 5 cells/hpf and 10(4) bacteria/ml, respectively. Each patient was randomly allocated either to CMD or CMZ group. There were 93 patients in CMD group and 100 patients in CMZ group. Clinical efficacy was evaluated based on the effect of treatment on bacteriuria and pyuria according to the criteria set by the UTI Committee, Japan. The response to CMD treatment was excellent in 18 cases (19.4%), moderate in 38 cases (40.9%) and poor in 37 cases (39.8%) with an overall effectiveness of 60.2%, whereas the response to CMZ was excellent in 19 cases (19.0%), moderate in 40 cases (40.0%) and poor in 41 cases (41.0%) with an overall effectiveness of 59.0%. No statistical significant difference was found between 2 treatment groups. Comparison of the bacteriological response between 2 groups showed that the eradication rate for strains of Gram-positive cocci were significantly higher in those patients treated with CMD. Gram-negative rods were eradicated from 68.4% of cases treated with CMD, and 78.0% of those with CMZ, but the difference was not significant. Adverse reactions were observed in 3 patients receiving CMD 1 case each of diarrhea, eruption and epigastric pain. Abnormality in laboratory tests was found in 6 patients in each treatment group. The results indicate that CMD is effective, safe and useful in the treatment of patients with complicated urinary tract infections, and its efficacy, safety and usefulness are comparable with those of CMZ.

Adolescent↗
PubMedDate not supplied

Uterine contractions: possible diagnostic pitfall at MR imaging.

A total of 206 nongravid patients with various gynecologic problems underwent pelvic magnetic resonance (MR) examinations that included both sagittal T2-weighted and contrast agent-enhanced T1-weighted images. MR images were retrospectively reviewed to identify changes in endometrial configuration on serial images obtained during the same MR examination. In 20 MR examinations (all in women of reproductive age), endometrial distortion due to myometrial bulging was noted on T2-weighted or contrast-enhanced T1-weighted images. It was absent on other MR images obtained at different times. Myometrial bulging exhibited low signal intensity in 18 examinations. The finding resembled adenomyosis or leiomyoma on T2-weighted or contrast-enhanced T1-weighted images. These results evidence the presence of transient myometrial bulging and transient low-intensity myometrium in the nongravid uterus. This phenomenon is thought to represent uterine contraction. Clinicians should be aware of the potential presence of transient low-signal-intensity myometrial bulging that could present diagnostic problems in the normal uterus.

Adolescent↗
PubMedDate not supplied

Epidural venous system (meningorachidian venous plexus) in juvenile amyotrophy of distal upper extremity: assessment with GD-DTPA enhanced volumetric MR study.

The epidural venous system (meningorachidian venous plexus) was analyzed utilizing gadolinium-diethylenetriamine pentaacetic acid (DTPA) (Gd-DTPA) enhanced volumetric magnetic resonance (MR) images in 11 patients with focal cervical spinal cord atrophy, clinically consistent with juvenile amyotrophy of distal upper extremity. In our series, all of the patients showed unusual posterior epidural venous enhancement at the C5-6 level, suggesting posterior epidural venous dilatation. Three patients also showed prominent dilatation of cervico-thoracic epidural veins surrounding the thecal sac. These MR findings were also demonstrated by spinal phlebography. Gd-DTPA enhanced MR images, especially high resolutional volumetric MR images, were efficient for evaluating these vessels. The observation of meningorachidian venous plexus along the disease course should be necessary for searching the pathogenesis of this disease.

Adolescent↗