Biomedical subjects
M Iwaki
Publications and source records attributed to M Iwaki.
Ion implantation into collagen-coated surfaces for the development of small diameter artificial grafts.
Ion implantation into collagen (Type I) coated inner surfaces of test tubes with a length of 50 mm and an inner diameter of 2 and 3 mm were performed to develop hybrid type small diameter artificial vascular grafts. To obtain information about the cellular response and chemical and physical structure of those collagen surfaces, several experiments such as platelets adhesion test, endothelial cell culture, analysis of amino acids and animal study were performed. He(+) ion implanted collagen coated specimen exhibited cell attachment and inhibit platelet adhesion. From these results, it was assumed that He(+) ions broke the ligands that correspond to platelet, and the ligands that correspond to endothelial cell adhesion still existed after ion implantation. It was suggested that platelets and cell attachment could be control individually by ion implantation into collagen.
Oxygen ion implantation at 20 to 2000 keV into polysulfone for improvement of endothelial cell adhesion.
The irradiation effects of oxygen on polysulfone have been investigated at energies of 20 keV, 150 keV and 2 MeV. The strong improvement of endothelial cell adhesion and proliferation is found on ion irradiated polysulfone at 20 keV. Such improvement is declined with increasing ion energy. The changes of surface color and free energy are strongly dependent on ion energy and dose. The formation of amorphous carbon phase is demonstrated by Raman spectroscopy and its degree is correspondent to the color changes observed. The formations of hydroxyl and carboxyl groups are confirmed by the attenuated total reflectance (ATR) FTIR spectroscopy. The depletions of heteroatoms are conjectured by detail analysis of X-ray photoelectron spectroscopy (XPS). Since no single one of these changes can be related directly to the improved adhesion and proliferation of endothelial cells on irradiated surface, we argue that the distribution of functional groups is crucial in promoting the adhesion of endothelial cells. Although the distribution cannot directly be detected at present, the irradiation effects were related to the results of TRIM simulation. The surface changes can be controlled by adjusting the size energy and dose of irradiating ion for the optimum morphology to cell adhesion.
Electrochemical characterization for ion-implanted materials surfaces.
Studies on the surface modification of materials by ion implantation have been carried out during the past 25 years in RIKEN. In this paper, results of electrochemical studies on the ion-implanted materials are described to realize the unique substances formed by the ion implantation. The ion implantation is used for compositional and structural surface modification of iron and carbon substrates. Voltammetric behavior of ion-implanted iron electrodes characterized effects of the ion implantation on anodic dissolution and passivation properties of the modified surfaces. Typical electrode reaction properties of ion-implanted carbon electrodes clearly were related to the effects of structural modification of the carbon surfaces.
The properties of BCN films formed by ion beam assisted deposition.
A study has been made on the formation and the properties of boron carbonnitride (BCN) thin films. The BCN films were produced by ion beam assisted deposition, in which boron and carbon were deposited by electron beam heating and nitrogen was supplied by ion implantation simultaneously. The mechanical properties of BCN films were measured using a ultra micro hardness tester and a friction tester. The atomic ratio and the structure of BCN thin films were estimated by means of X-ray photoelectron spectroscopy, laser Raman spectroscopy and Fourier transform infrared spectroscopy. As preliminary results, it was found that the BCN films are higher in hardness and lower in friction coefficient than diamond-like carbon (DLC) films. The mechanical properties are discussed with the relation of surface composition and structure.
Chromatographic and capillary electrophoretic methods for the analysis of nicotinic acid and its metabolites.
Methods for the assay of nicotinic acid (NiAc) and its metabolites in biological fluids using high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE) are reviewed. Most of the references cited in this review concern HPLC methods. A few CE methods that have been recently reported are also included. As these compounds are relatively polar and have a wide range of physico-chemical properties, the sample pre-treatment or clean-up process prior to analysis is included. Most HPLC methods using an isocratic elution system allow determination of a single or few metabolites, but gradient HPLC methods enable simultaneous determination of five to eight compounds. Simultaneous determination of NiAc including many metabolites in a single run can be achieved by CE. We also discuss the pharmacokinetics of NiAc and some of its metabolites.
Selective extraction of antenna chlorophylls, carotenoids and quinones from photosystem I reaction center.
By the ether treatment of lyophilized PSI pigment-protein complexes, all the carotenoids and the secondary acceptor phylloquinone (A1), and more than 90% of the Chl were removed to yield the PSI complex with 9-11 molecules of Chl per reaction-center unit. The complexes retained the primary electron donor and acceptor (P700 and A0), in addition to three FeS clusters (F(X), F(A) and F(B)), and showed an activity of highly efficient electron transfer when phylloquinone was reconstituted. The methods for the preparation and the characterization of the ether-extracted PSI complexes are reviewed in this article. We also review the studies done with this PSI preparation on (1) the identification of the absorption and fluorescence spectra of P700, (2) the nano- and picosecond reaction of A0 and A1, (3) the energy-gap dependency of the reaction rate between A0 and the artificial quinones reconstituted at the A1 site, (4) the direct excitation of P700 followed by the ultra-fast electron transfer from P700 to A0, and (5) the de- and re-stabilization of the PSI structure by the removal and reconstitution, respectively, of antenna Chl in the presence of certain lipids.
Stimulation of Bordetella pertussis adenylate cyclase toxin intoxication by its hemolysin domain.
The internalization of the N-terminal catalytic domain of Bordetella pertussis adenylate cyclase toxin (ACT) across the cytoplasmic membrane has been considered to occur independently from protein-protein interactions which can lead to oligomerization required for hemolytic activity by its C-terminal hemolysin domain. Here we report that when added in excess, this hemolysin domain stimulates the internalization, suggesting the involvement of protein-protein interactions in cell-invasive activity of ACT, as well as its hemolytic activity.
In vitro skin penetration and degradation of peptides and their analysis using a kinetic model.
The main purpose of this study was to estimate the net percutaneous absorption of physiologically active peptides in vitro. The degradation of two peptides, Leu-enkephalin (Enk) and Tyr-Pro-Leu-Gly amide (TPLG), during skin penetration and on the dermal side following penetration, and the prevention of degradation by some protease inhibitors, were investigated using rat skin in vitro. In addition, these permeation and degradation data were analyzed using a kinetic model. These peptides were rapidly degraded in the receptor fluid of a Franz diffusion cell (rate constant: 0.977 h(-1) for Enk and 0.250 h(-1) for TPLG). The addition of phenylmethylsulfonyl fluoride (PMSF) and phenanthroline and the pretreatment of skin with these inhibitors prevented almost completely any degradation in the receptor fluid and skin, respectively. The pretreatment of skin with PMSF and phenanthroline had no effect on the penetration of dextran (1000 Da). The degradation rate constant during skin penetration, calculated from the difference in the penetration rate constants via pretreated and untreated skins, was also high (0.037 h(-1) for Enk and 0.050 h(-1) for TPLG). A kinetic model including an input rate (zero-order), the permeation rate across the viable skin (first-order) and the degradation rate in skin (first-order) was sufficient to describe the apparent steady-state flux of the peptides through skin. We have, thus, established a method for measuring the true flux of peptides across skin in vitro and a kinetic model which simply describes the skin penetration of peptides.
Percutaneous penetration of ozagrel and the enhancement produced by saturated fatty acids.
The effects of a series of fatty acids on the percutaneous penetration of ozagrel (OZ), a selective thromboxane A2 synthetase inhibitor, through rat skin and the mechanism by which fatty acids enhance the skin penetration of OZ were examined in vitro. Lauric acid, at the fatty acid: OZ molar ratio of 2 : 1, was the most potent agent as far as increasing the skin penetration was concerned, with a flux 24-fold higher than that without fatty acid. A molar ratio of 3 : 1 also produced a large enhancing effect, comparable with that of a molar ratio of 2 : 1. When the gel formulation with lauric acid (molar ratio of 2 : 1) was applied to the skin for 6 h, the amount of drug penetrating into the skin was significantly increased compared with that after the formulations without lauric acid and with capric and palmitic acids. However, lauric acid did not change the apparent partition coefficient of OZ between n-heptane and phosphate buffer (pH 7.4). The 13C-NMR spectra of OZ was also unaffected by the addition of lauric acid, indicating that a complex or ion pair with lauric acid was not formed. A possible mechanism for the enhancing effect is the increased incorporation of lauric acid with OZ into the bulk lipid phase of the stratum corneum, where the fatty acid would act as a co-penetrant enhancing passage through the stratum corneum.
[Variables that influence visual acuity after macular hole surgery].
PURPOSE: To evaluate the variables that influence visual acuity and visual improvement after macular hole surgery. METHODS: Our study included 421 eyes in which maculor holes were successfully closed after surgery and followed up at least 1 year after the last surgery. Surgical techniques were conventional methods (Group 1: 350 eyes) with retinal pigment scalping of the macular hole basis added in the refractory cases (Group 2: 71 eyes). The variables used for the multiple regression were gender, age, preoperative visual acuity, hole stage, duration of symptoms, hole size, and axial length. RESULTS: The variables that most influenced postoperative visual acuity were as follows: Group 1: gender (r = -0.011, p = 0.016), age (r = -0.17, p = 0.005), preoperative visual acuity (r = 0.51, p < 0.0001), duration of symptoms (r = -0.015, p < 0.0001), and axial length (r = -0.090, p = 0.045). Group 2: age (r = -0.18, p = 0.047), and preoperative visual acuity (r = 0.47, p < 0.0001). CONCLUSIONS: The variables that influenced visual acuity and visual improvement after macular hole surgery were common. In Group 1: gender, age, preoperative visual acuity, duration of symptoms, and axial length; in Group 2: age and preoperative visual acuity.
[Incidence of reopening and variables that influence reopening after macular hole surgery].
PURPOSE: To evaluate the incidence and variables of reopening of macular holes after macular hole surgery. METHODS: Our study included 467 eyes in which maculor holes were successfully closed after surgery. Surgical techniques consisted of conventional methods (358 eyes) and scalping methods (109 eyes) with retinal pigment scalping of the macular hole basis added in such cases: reoperation, hole size (more than 0.4 disc diameter), duration of symptoms (more than 2 years). Long term incidence of reopening was predicted by life table method. After we compared reopened cases with non-reopened cases, the variables of gender, stage, biocular occurrence, age, duration of symptoms, hole size, preoperative visual acuity, refraction axial length ratio, and intraoperative retinal tears were used for the multiple regression. RESULTS: Reopening was found in 20 eyes (5.6%) treated by conventional methods and in 10 eyes (9.2%) treated by scalping methods. Survival ratio was 87% for the conventional methods in 6 years and 79% for the scalping methods in 5 years. The variables influencing reopening were as follows: conventional methods: gender (r = 0.065, p = 0.19), biocular occurrence (r = 0.12, p = 0.026), and refraction axial length ratio (r = -0.11, p = 0.045); scalping methods: hole size (r = 0.14, p = 0.25). CONCLUSIONS: Incidence of reopening in scalping methods was high. The variables that influenced reopening after macular hole surgery were biocular occurrence and refraction axial length ratio in conventional methods. The shape of the eye may be related to reopening.
[Factors related to initial success in macular hole surgery].
PURPOSE: To evaluate the factors of initial success in macular hole surgery. METHODS: This study included 526 eyes of 480 patients who underwent idiopathic macular hole surgery by one and the same surgeon. Surgical methods included conventional method (392 eyes), retinal pigment epithelium (RPE) scalping (61 eyes), internal limiting membrane (ILM) removal (62 eyes), and RPE scalping combined with ILM removal (11 eyes). To evaluate the factors of initial success multiple regression was performed using the variables of (gender, age, stage, duration of symptoms, hole size, axial length, and preoperative visual acuity). RESULTS: The rate of initial success was 81.4% in all eyes, 80.9% in the conventional method, 78.7% in RPE scalping, 83.9% in ILM removal, and 100% in RPE scalping combined with ILM removal. Significant factors of initial success were as follows: gender (r = -0.091, p = 0.053), age (r = -0.14, p = 0.0062), duration of symptoms (r = -0.23, p < 0.0001), hole size (r = -0.23, p < 0.0001), and axial length (r = -0.21, p < 0.0001) in the conventional method, hole size (r = -0.56, p = 0.0006) in ILM removal and stage (r = -0.43, p = 0.0011) and preoperative visual acuity (r = 0.30, p = 0.018) in RPE scalping. CONCLUSIONS: Significant factors of initial success were being male being young, shorter duration of symptoms, smaller hole size, and shorter axial length in the conventional method, smaller hole size in ILM removal and stage 4 and better preoperative visual acuity in RPE scalping method.
[Clinical features of idiopathic macular holes].
PURPOSE: The purpose of this study was to evaluate the clinical features of idiopathic macular holes. MATERIALS AND METHODS: The clinical features were examined in consequentive 526 eyes of 480 patients with idiopathic macular hole who underwent vitrectomy. RESULTS: Sixty-seven% of the patients were female. The mean onset age was 64.4 years of age and 60% of the cases were in their 60's at the time of onset. The mean refractive value was -0.66 dioptor and 40% of the cases were emmetropia with a refractive value between -1.0 dioptor and +1.0 dioptor. The onset age was positively correlated with refractive value. The visual acuity was negatively correlated with onset age, duration after onset, and the size of the macular hole. The duration was positively correlated with onset age. The size of the macular hole was positively correlated with age and duration. The factors for good visual acuity were determined by bilaterality, youth, or small size. Also we found the factors for large size of macular holes to be female gender, long duration of the hole, being in stage 4, and low visual acuity. CONCLUSIONS: The incidence of idiopathic macular hole is seen more in eyes of patients in their 60's and in emmetropic eyes. Patients with myopic eyes tend to have younger onset. The size of the macular hole in females tends to be larger than in males.
Characterization of the human dihydropyrimidinase-related protein 2 (DRP-2) gene.
The genes within the dihydropyrimidinase-related protein (DRP) family, were originally identified in humans by their homology to dihydropyrimidinase (DHP). Four members of this gene family, DRP-1, -2, -3 and -4, are expressed mainly in the fetal and neonatal brains of mammals and chickens, and have been implicated as intracellular signal transducers in the development of the nervous system. We isolated the human DRP-2 gene, and determined its transcriptional start site and exon/intron organization. The gene spanned more than 62 kb, and contained 14 exons with lengths ranging from 62 bp to 2606 bp. The transcriptional start site was determined by an RNase protection assay and 5' rapid amplification of cDNA ends (RACE), and a highly GC-rich promoter was identified that contained possible regulatory elements such as a TATA box, CAAT box and three GC boxes. Comparison of the phase and position of intron insertions within the human DRP-2 gene with those within DRP-1, DHP and two Caenorhabditis elegans DRP/DHP homologs, indicated that DRPs are more conserved in their exon/intron organization than DHP.
Epigallocatechin gallate and gallocatechin gallate in green tea catechins inhibit extracellular release of Vero toxin from enterohemorrhagic Escherichia coli O157:H7.
We studied the effects of six catechin derivatives (catechin, epigallocatechin, epicatechin, epicatechin gallate, epigallocatechin gallate (EGCg) and gallocatechin gallate (GCg)) in green tea on the production and extracellular release of Vero toxins (VTs) from enterohemorrhagic Escherichia coli (EHEC) cultured at 37 degrees C for 24 h. EGCg and GCg in the culture medium markedly inhibited extracellular VTs release from EHEC cells into the culture supernatant fluid at concentrations of 0.05 mg/ml or higher, as estimated by both the reversed passive latex agglutination assay and cytotoxic assay using Vero cells. Production and extracellular release of maltose binding protein, a periplasmic protein, into the culture supernatant were also inhibited by EGCg and GCg, indicating that their inhibitory effect on release from periplasm into the outer milieu is not specific to VTs, but general to the proteins accumulated in EHEC periplasm.
In vitro regioselective stability of beta-1-O- and 2-O-acyl glucuronides of naproxen and their covalent binding to human serum albumin.
beta-1-O- (NAG) and 2-O-glucuronides (2-isomer) of (S)-naproxen (NA) were prepared to determine which positional isomer(s) of the acyl glucuronide of NA is responsible for forming covalent adducts with human serum albumin (HSA). Their comparative stability and covalent binding adduct formation with HSA were investigated at pH 7.4 and at 37 degreesC. NA and its acyl glucuronides were simultaneously determined by HPLC. Three positional isomers were formed successively after incubation of NAG in the buffer only. However, when NAG was incubated with HSA (30 mg/mL), isomers other than the 2-isomer were formed in little or negligible quantities. In HSA solution, NAG (kd = 2.08 +/- 0.08 h-1) was four times less stable than 2-isomer (kd = 0.51 +/- 0.02 h-1). NAG was degraded by hydrolysis (khyd = 1.01 +/- 0.10 h-1) and isomerization (kiso = 1.07 +/- 0.07 h-1) to the same extent; however, hydrolysis was predominant for the 2-isomer (kd = 0.51 +/- 0.02 h-1). The incubation of both NAG and 2-isomer with HSA led to the formation of a covalent adduct; however, the adduct formation from the 2-isomer proceeded more slowly than that from NAG. The present results suggest that the covalent binding of NA to HSA via its acyl glucuronides proceeds through both transacylation (direct nucleophilic displacement) and glycation mechanisms; NAG rapidly forms an adduct that may be unstable, and the protein adduct from the 2-O-acyl glucuronide is as important for the covalent binding as those from the 1-O-acyl glucuronides.
Suppression of platelet aggregation by Bordetella pertussis adenylate cyclase toxin.
The effect of Bordetella pertussis adenylate cyclase toxin (ACT) on platelet aggregation was investigated. This cell-invasive adenylate cyclase completely suppressed ADP (10 microM)-induced aggregation of rabbit platelets at 3 micrograms/ml and strongly suppressed thrombin (0. 2 U/ml)-induced aggregation at 10 micrograms/ml. The suppression was accompanied by marked increase in platelet intracellular cyclic AMP (cAMP) content and was diminished by the anti-ACT monoclonal antibody B7E11. A catalytically inactive point mutant of ACT did not show the suppressive effect. Since an increase of cAMP content is a known cause of platelet dysfunction, these results indicate that the observed platelet inactivation was due to the catalytic activity of ACT through increase of intracellular cAMP.