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Biomedical subjects

M Iwatsuki

Publications and source records attributed to M Iwatsuki.

At least 19 recordsLinked to original sources
PubMed2001

Physicochemical speciation of molybdenum in rain water.

A combination of a sensitive catalytic determination method with filtration and ultrafiltration has been used for the physicochemical speciation of molybdenum in natural and synthetic rain water samples. The concentration (CL) of labile molybdenum was evaluated by a direct catalytic determination. The total concentration (CT ) of molybdenum was determined after the acid decomposition of the sample to calculate the non-labile concentration (CT-CL). From the speciation results, molybdenum species in the successive rainfall sample were found in a fraction with smaller molecular weights < 10(3) Da and characterized as labile forms, i.e. simple molybdate ions. Non-labile molybdenum existed in particulate matter (> or = 0.45 microm in particle size) and distributed predominantly in the initial rainfall sample. The coprecipitation with Fe(III) hydroxide contributed to the formation of the non-labile molybdenum. In the initial rainfall sample, a small part of molybdenum was labile in the particle fraction (> or = 0.45 microm). This type of molybdenum was associated with the formation of humic iron aggregates.

Air Pollutants↗
PubMed2000

Observations of sudden structural-changes of the faulted-halves of the DAS structure on quenched Si(1 1 1) by STM

We have carried out scanning tunneling microscopy (STM) observations of unreconstructed regions on quenched Si(1 1 1) surfaces at 380 degrees C at a scanning speed of 1.7 s per frame. In the regions, it is found that single faulted-halves of the dimer-adatom-stacking-fault (DAS) structure are formed isolatedly or at the edges of the surrounding DAS domains sharing one corner hole. In such "living" regions, we have succeeded to observe sudden structural changes of the faulted-halves during line scans in single frames of STM images.

Journal Article↗
PubMed1999

Comparative Surface Studies at Atomic Resolution with Ultrahigh Vacuum Variable-Temperature Atomic Force and Scanning Tunneling Microscopes.

: With the ultrahigh vacuum variable-temperature scanning tunneling microscope (UHV-VT-STM), atomic-level observation has been achieved. An ultrahigh vacuum atomic force microscope (UHV-AFM) has also been developed, with success in obtaining atom images where observation in noncontact (NC) mode with a frequency modulation (FM) detection method was attempted. Using the FM detection method in the constant oscillation amplitude of the cantilever excitation mode, we have obtained atomic-resolution images of Si(111) 7 x 7 structures and Si(100) 2 x 1 structures and other structures together with STM images in an ultrahigh vacuum environment. Also shown here are contact potential difference (CPD) images using the NC-AFM method.

Journal Article↗
PubMed1995

Action of beta-carotene as an antioxidant against lipid peroxidation.

The action and activity of beta-carotene as a radical-scavenging antioxidant against lipid peroxidation have been studied. beta-Carotene suppressed the free-radical-mediated oxidations of methyl linoleate in benzene solution and soybean phosphatidylcholine liposomal membranes in aqueous dispersions in a dose-dependent manner, but the antioxidant activity of beta-carotene was much smaller than that of alpha-tocopherol. beta-Carotene was 32 times less reactive toward peroxyl radical than alpha-tocopherol and approximately as reactive as 2,6-di-tert-butyl-4-methylphenol in benzene solution. Toward carbon-centered radical, beta-carotene was 11 times less reactive than alpha-tocopherol. When beta-carotene and alpha-tocopherol were present together in homogeneous solution, alpha-tocopherol was consumed predominantly and beta-carotene was spared. When they were incorporated simultaneously into the same dimyristoyl phosphatidylcholine liposomal membranes and the radicals were formed in the aqueous phase, alpha-tocopherol was consumed faster than beta-carotene, but the sparing efficacy was much smaller than in homogeneous solution. On the contrary, beta-carotene was consumed faster than alpha-tocopherol when the radicals were generated within the lipophilic compartment of the membranes, implying that beta-carotene is relatively more favorable than alpha-tocopherol for scavenging lipophilic radicals within the membranes. In contrast to an efficient synergistic inhibition by a combination of alpha-tocopherol and ascorbic acid, cooperative interaction between beta-carotene and ascorbic acid was not observed. beta-Carotene underwent autooxidation to give polymeric products and the rate of consumption of beta-carotene increased with increasing concentrations of itself and oxygen and decreased with increasing concentration of lipids. The formation of polymeric products was confirmed by gel permeation chromatography. It was concluded that beta-carotene is less potent as an antioxidant than alpha-tocopherol because beta-carotene is less reactive toward peroxyl radical than alpha-tocopherol and the stable beta-carotene radical reacts with oxygen to give beta-carotene peroxyl radical which is not stable but able to attack lipid to continue chain oxidation. The higher antioxidant activity of beta-carotene at lower oxygen pressure is attributed primarily to an unfavorable formation of beta-carotene peroxyl radical at higher oxygen pressure rather than a higher reactivity of beta-carotene toward carbon-centered radical than peroxyl radical.

Antioxidants↗
PubMed1995

Alpha-tocopherol mediated peroxidation in the copper (II) and met myoglobin induced oxidation of human low density lipoprotein: the influence of lipid hydroperoxides.

The principal antioxidant in human LDL, alpha-tocopherol, is converted to the alpha-tocopheroxyl radical after reaction with peroxyl radicals or Cu2+, and, if it does not terminate with peroxyl radicals, could initiate lipid peroxidation; a phenomenon called 'tocopherol mediated peroxidation'. Only in the presence of Cu2+ and low levels of lipid hydroperoxides was an alpha-tocopherol dependent decrease in the resistance of LDL to oxidation detected. This suggests that tocopherol mediated peroxidation will probably not contribute significantly as a pro-oxidant process in those individuals most at risk of developing atherosclerosis through an oxidative mechanism.

Azoles↗
PubMed1994

Effects of solvents and media on the antioxidant activity of alpha-tocopherol.

The effects of solvents and media on the antioxidant activity of alpha-tocopherol were studied. The antioxidant activities of alpha-tocopherol in different solvents decreased in the order of acetonitrile = hexane > ethanol = methanol, which indicates that the antioxidant activity of alpha-tocopherol is smaller in protic solvent than in aprotic solvent. The antioxidant activity of 2-(4,8,12-trimethyltridecyl)-5-hydroxy-2,4,6,7-tetramethylindan , which has similar structure to alpha-tocopherol but does not have ether oxygen, was also measured in protic and aprotic solvents. Its antioxidant activity was smaller than that of alpha-tocopherol in every solvent, but interestingly, substantially the same solvent effects were observed. These results show that the hydrogen bonding between the protic solvent and either oxygen is not important but that the hydrogen binding between protic solvent and phenolic group reduces the activity of alpha-tocopherol. Antioxidant activities of alpha-tocopherol in micelle system and liposomal membrane were markedly reduced compared with that in homogeneous solution. Solvent effect on the alpha-tocopheroxyl radical was also studied by using electron spin resonance. The hyperfine splitting constants of a5CH3H and a7CH3H were smaller in protic solvent than in aprotic solvent, which shows that lone-pair orbital energy on 5-CH3 and 7-CH3 is smaller in protic solvent. The ESR spectra of alpha-tocopheroxyl radical in liposomal membrane and micelle were similar to those observed in aprotic solvent and in protic solvent, respectively, suggesting that alpha-tocopheroxyl radical is located predominantly in the lipophilic domain of the liposomal membrane but in or closer to water phase of micelle aqueous suspensions.

Antioxidants↗
PubMed1994

Fibroblast attachment to Arg-Gly-Asp peptide-immobilized poly(gamma-methyl L-glutamate).

The attachment of MRC-5 human fibroblasts was investigated on poly(gamma-methyl L-glutamate) (PMLG), and upon cell adhesion peptides Arg-Gly-Asp-Ser (RGDS)- and Gly-Arg-Gly-Asp-Ser (GRGDS)-immobilized PMLG (RGDS-PMLG and GRGDS-PMLG). The peptides were immobilized by their N-terminal amine to activated PMLG surfaces. Prior to peptide immobilization, the aminolysis of PMLG surfaces was performed with hydrazine hydrate (HA), ethylenediamine (EDA), and hexamethylenediamine (HMDA) and was followed by the activation with hexamethylene diisocyanate. Surface characterization of these films was carried out by means of a Fourier transform IR (FT-IR) spectrometer equipped with an attenuated total reflectance (ATR) attachment. The amount of immobilized RGDS could be controlled by the reaction time of the aminolysis. The effects of HA, EDA, and HMDA as a spacer on the cell attachment were also investigated, and it was suggested that a longer spacer promoted the cell attachment via specific receptor-ligand interaction.

Amino Acid Sequence↗
PubMed1993

Altered cartilage phenotype expressed during intramembranous bone formation.

The sequential phenotypic expression occurring during intramembranous bone formation was investigated using the tooth extraction socket created in rat alveolar bone in vivo. The differential expression of bone extracellular matrix genes, such as collagen I and osteocalcin, was confirmed by RNA transfer blot analysis and in situ hybridization during the active healing period of the bony socket. To clarify the possible involvement of the chondrogenic phenotype during the process of intramembranous bone formation, the expression of cartilage collagen II and IX was further examined in this model. It was found that both alpha 1(II) and alpha 1(IX) mRNAs were present, but the alpha 1(IX) mRNA was a transcript from the downstream start site/promoter, which is a different site in the alpha 1(IX) gene from that used in hyaline cartilage. In situ hybridization indicated that the alpha 1(IX) message was expressed by cells associated with bone matrix in the early formation stage. This finding led to the investigation of type IX collagen expression by osteogenic cells isolated from newborn rat calvariae, in which only the truncated form of alpha 1(IX) mRNA was indicated by RNA transfer analysis. The expression of collagen II and a truncated form of collagen IX may represent an early phenotypic feature of osteoblast differentiation.

Animals↗
PubMed1993

Biodegradation of random copolypeptide membranes consisting of N-hydroxyalkyl L-glutamine as one component.

Two component random copolypeptide membranes, consisting of N-hydroxyalkyl L-glutamine and L-alanine or L-leucine were prepared by carrying out aminolysis reactions with 2-amino-1-ethanol (E) or 5-amino-1-pentanol (Pe), together with a cross-linking reaction with 1,8-octamethylenediamine (OMDA) on membranes of the starting copolymers consisting of gamma-benzyl L-glutamate (B) and L-alanine (A) or L-leucine (L). The relationships between their bulk structure and membrane properties were investigated, such as the swelling ratio in water, aqueous vapour permeability, tensile properties and enzymatic degradation behaviour of the membranes in a pseudo-extracellular fluid (PECF). The tensile properties of the hydrophilic membranes were highly dependent on the swelling ratio of PECF, and the hydrophobicity of the side chains, whose behaviour was typical of an elastomer. We showed that a common relation was obtained between the rate of water vapour permeability and the swelling ratio of membranes in PECF despite the difference of the nature of the side chains. Biodegradation of these membranes in vitro by bromelain indicated that the degradation was a bulk rather than a surface phenomenon, and that the rate of degradation was also highly dependent on the swelling ratio of samples and on the hydrophobicity of the side chains of samples.

Alanine↗
PubMed1993

Antioxidant activities of natural and synthetic carbazoles.

The antioxidant activities of various natural and synthetic carbazoles were studied in the oxidations of methyl linoleate in homogeneous solution and soybean phosphatidylcholine (PC) liposomes in aqueous dispersion induced by free radicals. Carazostatin, 1-heptyl-3-hydroxy-2-methyl carbazole, which was isolated from a culture of Streptomyces chromofuscus, was found to be a strong antioxidant in both oxidation systems. Carbazomycin B, 4-hydroxy-3-methoxy-1,2-dimethylcarbazole, showed a moderate antioxidant activity. Other derivatives from these carbazoles without a free hydroxy group did not suppress the oxidation appreciably. The antioxidant activity of carazostatin in the oxidation of soybean PC liposome was stronger than that of alpha-tocopherol, although the latter exhibited stronger antioxidant activity than carazostatin in the oxidation in homogeneous solution. Vitamin C acted as a synergist in combination with carazostatin in the oxidation of soybean PC liposomes.

Antioxidants↗
PubMed1990

Biodegradation of copoly(L-aspartic acid/L-glutamic acid) in vitro.

The preparation of copolypeptides consisting of L-aspartic acid and L-glutamic acid was performed to determine the effects of copolymer composition and sequential distributions on the rate of degradation by papain in a PECF (pseudoextracellular fluid) at pH 4.75 and 7.40, at 37.0 degrees C, to simulate in vivo polymer degradation. Random copolymers consisting of beta-benzyl L-aspartate and gamma-benzyl L-glutamate were synthesized by the N-carboxyanhydride method. Water-soluble copolymers were obtained by successive reactions of side chains by anhydrous HBr treatment. All the samples were found to be degraded by random chain scission with papain. Further, the degradation data for the samples followed the Michaelis-Menten rate law, being the first order in papain concentration. The nature of side chains are important to the rate of degradation by papain and it was controlled by the comonomer composition as well as the sequential distribution of comonomers in the copolymer chains.

Aspartic Acid↗