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Biomedical subjects

S Iwasaki

Publications and source records attributed to S Iwasaki.

At least 19 recordsLinked to original sources
PubMed1995

Identification of a major cytokinin in coconut milk.

A major cytokinin found in coconut milk was isolated by using the tobacco callus growth-promoting assay as a guide during purification. The structure of the factor was determined to be 14-O-(3-O-[beta-D-galactopyranosyl-(1-->2)-alpha-D-galactopyranosyl-(1-- >3)- alpha-L-arabinofuranosyl]-4-O-(alpha-L-arabinofuranosyl)-beta-D- galactopyranosyl)-trans-zeatin riboside [G3A2-ZR] by various NMR techniques, including heteronuclear multiple bond connectivity by 2D multiple quantum NMR (HMBC), as well as mass spectroscopy and sugar analysis. The optimum concentration of G3A2-ZR for cytokinin activity in the tobacco callus assay was estimated to be 5 x 10(-6) M, so that G3A2-ZR is one order of magnitude more potent than 1,3-diphenylurea and one order less potent than zeatin riboside. At least 20% of the cytokinin activity of coconut milk could be attributed to G3A2-ZR.

Carbohydrate Conformation↗
PubMed1995

Homogeneous quantitative assay of hepatitis C virus RNA by polymerase chain reaction in the presence of a fluorescent intercalater.

We have developed a homogeneous quantitative assay of DNA/RNA by performing PCR in the presence of an oxazole yellow derivative, a fluorescent DNA intercalative dye, and monitoring the fluorescence intensity of the PCR reaction mixture during PCR cycles. We have demonstrated the applicability of this assay by use it to quantify hepatitis C virus (HCV) RNA of serum samples from patients with chronic hepatitis C. This assay gave efficient and reproducible results in a clinically useful dynamic range below 10(-6) copies of HCV RNA for interferon therapy.

Base Sequence↗
PubMed1995

Ustiloxins, new antimitotic cyclic peptides: interaction with porcine brain tubulin.

Biochemical and electron microscopic studies demonstrated that ustiloxins A-D, which are antimitotic 13-membered cyclic peptides produced by the rice plant pathogen Ustilaginoidea virens, strongly inhibited the polymerization of porcine brain tubulin in vitro and depolymerized pre-formed microtubules. The IC50 values of polymerization inhibited by ustiloxins A-D were determined to be 0.7, 2.8, 4.4 and 6.6 microM, respectively, under the experimental conditions used, indicating that ustiloxin A is the most potent inhibitor of tubulin polymerization currently known. Ustiloxins A-C were found to inhibit the binding of radiolabelled rhizoxin to tubulin with inhibition constants (Ki) of 0.08, 0.13 and 0.23 microM, respectively, and also inhibited the binding of radiolabelled phomopsin A as strongly as rhizoxin. These results suggest that the binding site of ustiloxins is identical with that of rhizoxin.

Amino Acid Sequence↗
PubMed1995

Evidence for Th2 cell-mediated suppression of antibody responses in transgenic, beef insulin-tolerant mice.

Clonal deletion, anergy and suppression have all been considered mechanisms of immunological tolerance. Although adoptive transfer of immunosuppression has been shown to occur in the periphery, particularly for transplantation tolerance, it has proven difficult to characterize this phenomenon further, due to the lack of suppressor T cell clones. To characterize tolerance towards a physiological soluble antigen, we constructed beef insulin (BI) transgenic (Tg) BALB/c (H-2d) mice, in which the BI transgene is expressed in pancreatic beta cells. These Tg mice were tolerant to BI immunization at the level of both humoral and cell-mediated immune responses. Adoptive transfer of splenocytes from Tg mice into normal syngeneic BALB/c mice demonstrated that the reduction in antibody production is regulated by transferred T cells. The cytokine profile of T cell clones obtained after selection in vitro demonstrated dominant Th1 clones from normal non-Tg mice and dominant Th2 clones from Tg mice. Some Th2 clones (CD4+) from Tg mice produced significant suppression of antibody production after adoptive transfer into normal syngeneic BALB/c mice. These data confirm the existence of Th2 regulatory T cells in vivo in a model of peripheral tolerance to a physiological soluble antigen as a potential mechanism for self tolerance.

Animals↗
PubMed1995

Nitric oxide and endothelin in pathophysiological settings.

The role of the endothelium is now known to encompass the generation of many potent cytokines which impact endothelial cells, adjacent tissue such as smooth muscle cells, and distant sites in an autocrine, paracrine, and endocrine manner, respectively. This review addresses two of these cytokines, nitric oxide and endothelin, and describes how each effects the functions of endothelial cells, including regulation of platelet aggregation and coagulation, regulation of vasomotor tone, modulation of inflammation, and the regulation of cellular proliferation. The emphasis is on the increasingly recognized importance of the autocrine and paracrine mechanisms by which nitric oxide and endothelin act. In particular, autoinduction of endothelin is proposed as a central mechanism underlying endothelin's renowned effects. Additionally, specific nitric oxide/endothelin interactions are discussed by which each cytokine modulates the production and actions of the other. The net effect observed in a variety of physiological and pathophysiological settings, therefore, reflects a balance of these opposing functions.

Cell Division↗
PubMed1995

Osteoplastic changes in attic cholesteatoma.

Eighty-nine cases of attic type cholesteatoma were operated on during a three and a half-year period. Of these, eight cases were characterized by bony tissue proliferation at the aditus ad antrum or mastoid antrum. Sex, age, and hearing levels were not significant in these cases. Bony fixation of the incus and the malleus was seen in six cases. Bony tissue blocked further expansion of attic cholesteatoma at the aditus in four cases, narrowed the epithelial tract to the antrum in two cases, and completely separated the cholesteatoma into two cholesteatomas in two cases. Infectious stimuli, at an early stage of the disease, might stimulate such osteoplastic activity at the aditus. Axial CT scans give useful information regarding structure before surgery.

Adult↗
PubMed1995

Ribosylation by mycobacterial strains as a new mechanism of rifampin inactivation.

Several fast-growing Mycobacterium strains were found to inactivate rifampin. Two inactivated compounds (RIP-Ma and RIP-Mb) produced by these organisms were different from previously reported derivatives, i.e., phosphorylated or glucosylated derivatives, of the antibiotic. The structures of RIP-Ma and RIP-Mb were determined to be those of 3-formyl-23-[O-(alpha-D-ribofuranosyl)]rifamycin SV and 23-[O-(alpha-D-ribofuranosyl)]rifampin, respectively. To our knowledge, this is the first known example of ribosylation as a mechanism of antibiotic inactivation.

Inactivation, Metabolic↗
PubMed1995

Possible involvement of peripheral-type benzodiazepine receptors in erythroid differentiation of human leukemia cell line, K562.

Possible involvement of the peripheral-type benzodiazepine receptor (PBR) in hemin/protoporphyrin-induced erythroid differentiation of human leukemia K562 cells was investigated by the use of the ligands, diazepam and PK11195. Diazepam itself exhibited differentiation-inducing activity on K562 cells. The PBR-specific antagonist, PK11195, dose-dependently inhibited both diazepam-induced and hemin/protoporphyrin-induced K562 cell differentiation. The results imply that PBR is involved in the erythroid differentiation of K562 cells.

Cell Differentiation↗
PubMed1995

Endothelin A receptor mediates functional but not structural damage in chronic cyclosporine nephrotoxicity.

Chronic treatment with cyclosporine (CsA) is limited not only by glomerular hypofiltration but also by structural damage. The pathogenesis of these nephrotoxicities was studied in a model of chronic CsA-induced renal damage. Salt-depleted rats were treated with daily CsA (15 mg/kg sc) for approximately 3 weeks, at which time renal function was measured and kidneys were harvested for morphologic assessment. A separate group of rats (CsA + BQ123) were identically treated with CsA but in addition also received simultaneous treatment with a specific endothelin A (EtA) receptor antagonist, BQ123, which was continuously delivered via sc osmotic pump (1 mg/kg per hour) and maintained throughout the study. Chronic CsA treatment caused profound functional and structural damage, although blood pressure was normal (102 +/- 6 mm Hg); GFR was 0.05 +/- 0.02 mL/min per 100 g body wt, and RPF was 0.15 +/- 0.06/100 g body wt. Renal injury was scored on a scale of 0 to 4 and showed dilation/vacuolization of 1.07 +/- 0.29 and tubulointerstitial fibrosis of 0.78 +/- 0.17. Arteriolopathy was present in 78 +/- 4% of arterioles. Chronic antagonism of the EtA receptor preserved renal function: GFR was 0.15 +/- 0.03 mL/min per 100 g body wt, and RPF was 0.32 +/- 0.08/100 g body wt (P < 0.05 for GFR versus CsA). Blood pressure was not affected: 104 +/- 8 mm Hg.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Retinal distribution of attention.

Spatial distribution of attention around a fixation point was investigated by comparing cued vs noncued conditions. The curve of retinal locations for the cued condition was flatter than that of the noncued condition, indicating attentional spotlight is focused around the fixation point.

Attention↗
PubMed1995

Handedness trends across age groups in a Japanese sample of 2316.

Hand-preference data of 2316 Japanese were analyzed by age groups, sex, and familial sinistrality. Right-hand preference increased across age groups at least up to 30 years for men, while women showed relatively stable and stronger preference for right-hand use. Unlike some Western studies, no linear trends across age groups were found for both sexes. Declining cultural censorship against left-handedness would not be responsible for the trends, since there was no evidence indicating such a decline in Japan. Hypotheses of reduced longevity and life-long adaptation to the right-handed world are not satisfactory either, since both hypotheses assume a linear trend spanning the entire life span. Thus, it seems that a single-factor hypothesis which explains all the results by resorting to a single cause does not account for the complex results found in this and other studies.

Adolescent↗
PubMed1995

Rifampicin inactivation by Bacillus species.

The ability of strains of Bacillus, Staphylococcus, Pseudomonas, and Escherichia coli to inactivate rifampicin was tested. Most Bacillus strains were found to inactivate rifampicin. Two modes of inactivation were identified; one was phosphorylation and the other involved decolorization. Presence or absence of either mechanism appeared unrelated to the phylogenetic relatedness of strains. None of the other organisms could inactivate this antibiotic.

Bacillus↗
PubMed1995

Suppression of pannus-like extension of synovial cells by lipid-derivatized chondroitin sulphate: in vitro and in vivo studies using Escherichia coli-induced arthritic rabbits.

In rheumatoid arthritis, pannus formation resulting from synovial inflammation is a major factor in cartilage destruction. The ability of arthritic synovial cells to undergo pannus formation depends upon their initial adhesion to the partially deformed cartilage surfaces. Our recent studies using various lipid-derivatized glycosaminoglycans have revealed a preeminent inhibitory activity of phosphatidyl ethanol amine-derivatized chondroitin sulphate (CS-PE) toward cell-matrix adhesion. Here we evaluate whether CS-PE may protect articular cartilage from pannus extension in different in vitro and in vivo model systems using Escherichia coli 0:14-induced arthritis in rabbits and the articular cartilage explants, synovial tissues, and synovial cells obtained from them. These studies showed that CS-PE suppressed the in vivo pannus-like extension on cartilage surfaces, as well as the in vitro extension of the synovial cell layer on both CS-PE treated culture plates and cartilage explants. The results suggest that native chondroitin sulphate proteoglycans in the surface of normal articular cartilage play an important role in protecting the tissues from pannus extension and that the CS-PE immobilized onto partially eroded cartilage can mimic the inhibitory action of native chondroitin sulphate proteoglycans.

Animals↗
PubMed1995

[Spinal canal bleeding in hemophilia A].

Case 1: Sensory and motor paralysis below the L3 level developed in a moderate hemophilia A due to spinal epidural bleeding following lumbar anesthesia for the resection of retro-peritoneal hematoma. By the treatment with cryoprecipitates, the patient recovered to walk with sticks after laminectomy. Case 2: the patient had severe hemophilia A with 220 Bethesda units/ml of inhibitor. The patient suffered from epidural and intramedullary spinal bleeding from C3 to C7 and developed tetraplegia. Since the inhibitor titer was high, infusion therapy with FEIBA was performed. Paralysis gradually reduced to the T5 level, but the patient had both sensory and motor paralysis of the extremities. It is required that an effective hemostastic treatment for spinal canal bleeding in hemophilia A with high-responder inhibitor is established.

Adolescent↗
PubMed1994

Mutation of a fungal aspartic proteinase, Mucor pusillus rennin, to decrease thermostability for use as a milk coagulant.

Mutagenesis of a fungus Mucor pusillus, a producer of an aspartic proteinase named Mucor pusillus rennin (MPR), was performed to obtain the mutated enzymes with decreased thermostability, which is desirable for practical use of the enzyme as a milk coagulant for cheese manufacturing. A fungal mutant strain which produced the mutant enzyme with distinctly reduced thermostability was isolated. Two different mutant alleles of the mpr gene, one with a single amino acid exchange of Ala101 for Thr and the other of Gly186 for Asp, were cloned out of this mutant strain. The mutated mpr genes were expressed in Saccharomyces cerevisiae under the control of the yeast GAL7 promoter to produce the active enzymes in extracellular medium. Both of the mutations, especially Gly186Asp, were confirmed to cause a marked decrease in thermostability of the enzyme. All mutants possessing exchanges of Gly186 for various amino acids by site-directed mutagenesis showed a decrease in thermostability, indicating involvement of this residue to maintain a conformation of the enzyme. A double mutant having the both exchanges, Ala101Thr and Gly186Asp, in a single molecule showed the lowest thermostability without decrease in the enzymatic activity as well as the relative ratio of clotting to proteolytic activity.

Amino Acid Sequence↗