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Masaki Azuma

Publications and source records attributed to Masaki Azuma.

14 recordsLinked to original sources
PubMed2005

A quantitative matrigel assay for assessing repopulating capacity of prostate stem cells.

Homeostasis of prostate tissue is maintained by stem cells, although such cells have not been well characterized. Here, we report establishment of such a method using matrigel. Matrigel containing a single-cell suspension from adult prostatic cells was subcutaneously grafted into the flank of nude mice. Prostatic duct-like structures derived from donor tissue were observed in the gel 2 weeks after transplantation. Luminal and basal cells observed in the gel expressed several markers characteristic of prostatic and/or epithelial cells. When a mixture with both EGFP-positive and negative prostate cells was transplanted, prostatic ducts consisted of either EGFP-positive or negative cells and chimeric patterns were rarely observed, suggesting that ducts were reconstituted from a single cell. Stem cell number and function were also evaluated by competition with control cells. Overall this method revealed that cells localized in the proximal portion in prostate ducts had higher reconstitution capacity than those in the distal portion. We conclude that prostate stem/progenitor cells exist and that our method is applicable to analysis of prostate stem cells, epithelial mesenchyme interactions, and prostate cancer stem cells.

Animals↗
PubMed2005

Magnetic properties of isostructural BaCoP2O7, BaNiP2O7, and BaCuP2O7 studied with dc and ac magnetization and specific heat.

Magnetic properties of three isostructural compounds BaMP2O7 (M = Co, Ni, and Cu) were investigated by dc and ac magnetization and specific heat measurements. BaCuP2O7 was shown to be an excellent quasi-one-dimensional linear-chain Heisenberg antiferromagnet with an exchange constant (J/kB) of 103.8 K (Hamiltonian H = J Sigma SiS(i+1)) and a temperature for the long-range magnetic order (TN) of 0.81 K giving the ratio kBTN/J = 0.78%. BaCoP2O7 and BaNiP2O7 exhibited long-range antiferromagnetic order at TN = 10.4 and 10.1 K, respectively. BaCoP2O7 and BaNiP2O7 showed a large contribution of the short-range correlation above TN. BaNiP2O7 remained in the antiferromagnetic state up to 90 kOe at 2 K, whereas BaCoP2O7 demonstrated two metamagnetic phase transitions at about 52 and 71 kOe at 2 K if the magnetic field was parallel to the easy direction. BaMP2O7 melted incongruently at 1323 K (M = Co), 1344 K (M = Ni), and 1338 K (M = Cu).

Journal Article↗
PubMed2005

Loss of Tie2 receptor compromises embryonic stem cell-derived endothelial but not hematopoietic cell survival.

Tie2 is a receptor-type tyrosine kinase expressed on hematopoietic stem cells and endothelial cells. We used cultured embryonic stem (ES) cells to determine the function of Tie2 during early vascular development and hematopoiesis. Upon differentiation, the ES cell-derived Tie2+ Flk1+ fraction was enriched for hematopoietic and endothelial progenitor cells. To investigate lymphatic differentiation, we used a monoclonal antibody against LYVE-1 and found that LYVE-1+ cells derived from Tie2+ Flk1+ cells possessed various characteristics of lymphatic endothelial cells. To determine whether Tie2 played a role in this process, we analyzed differentiation of Tie2-/- ES cells. Although the initial numbers of LYVE-1+ and PECAM-1+ cells derived from Tie2-/- cells did not vary significantly, the number of both decreased dramatically upon extended culturing. Such decreases were rescued by treatment with a caspase inhibitor, suggesting that reductions were due to apoptosis as a consequence of a lack of Tie2 signaling. Interestingly, Tie2-/- ES cells did not show measurable defects in development of the hematopoietic system, suggesting that Tie2 is not essential for hematopoietic cell development.

Animals↗
PubMed2005

Investigation of the crystal structure and the structural and magnetic properties of SrCu2(PO4)2.

SrCu2(PO4)2 was prepared by the solid-state method at 1153 K. Its structure was solved by direct methods in the space group Pccn (No. 56) with Z = 8 from synchrotron X-ray powder diffraction data measured at room temperature. Structure parameters were then refined by the Rietveld method to obtain the lattice parameters, a = 7.94217(8) A, b = 15.36918(14) A, and c = 10.37036(10) A. SrCu2(PO4)2 presents a new structure type and is built up from Sr2O16 and Cu1Cu2O8 units with Cu1...Cu2 = 3.256 A. The magnetic properties of SrCu2(PO4)2 were investigated by magnetic susceptibility, magnetization up to 65 T, Cu nuclear quadrupole resonance (NQR), electron-spin resonance, and specific heat measurements. With spin-dimer analysis, it was shown that the two strongest spin-exchange interactions between Cu sites result from the Cu1-O...O-Cu2 and Cu2-O...O-Cu2 super-superexchange paths with Cu1...Cu2 = 5.861 A and Cu2...Cu2 = 5.251 A, and the superexchange associated with the structural dimer Cu1Cu2O8 is negligible. The magnetic susceptibility data were analyzed in terms of a linear four-spin cluster model, Cu1-Cu2-Cu2-Cu1 with -2J(1)/kB = 82.4 K for Cu1-Cu2 and -2J(2)/k(B) = 59 K for Cu2-Cu2. A spin gap deduced from this model (Delta/kB = 63 K) is in agreement with that obtained from the Cu NQR data (Delta/kB = 65 K). A one-half magnetization plateau was observed between approximately 50 and 63 T at 1.3 K. Specific heat data show that SrCu2(PO4)2 does not undergo a long-range magnetic ordering down to 0.45 K. SrCu2(PO4)2 melts incongruently at 1189 K. We also report its vibrational properties studied with Raman spectroscopy.

Journal Article↗
PubMed2005

Designed ferromagnetic, ferroelectric Bi(2)NiMnO(6).

A newly designed ferromagnetic, ferroelectric compound, Bi(2)NiMnO(6), was prepared by high-pressure synthesis at 6 GPa. The crystal structure, as determined by synchrotron X-ray powder diffraction, is a heavily distorted double perovskite with Ni(2+) and Mn(4+) ions ordered in a rock-salt configuration. The presence of 6s(2) lone pairs of Bi(3+) ions and the covalent Bi-O bonds give ferroelectric properties with T(CE) of 485 K, while -Ni(2+)-O-Mn(4+)-O-Ni(2+)- magnetic paths lead to a ferromagnetism with T(CM) of 140 K. This simple material design to distribute two magnetic elements with and without e(g) electrons on B sites of Bi- and Pb-based perovkites can be applied to other Bi(2)M(2+)M'(4+)O(6) and Pb(2)M(3+)M'(5+)O(6) systems to search for newer ferromagnetic ferroelectrics.

Journal Article↗
PubMed2005

Low-dimensional ferromagnetic properties of SrCuV2O7 and BaCuV2O7.

The crystal structure of isostructural SrCuV(2)O(7) and BaCuV(2)O(7) consists of one-dimensional (1D) zigzag chains of Cu atoms with next-nearest-neighbor interaction. The main intrachain interaction was found to be ferromagnetic and estimated at 4.6 K (Hamiltonian H approximately -2J). SrCuV(2)O(7) and BaCuV(2)O(7) are new examples in the scanty family of 1D ferromagnets. Isothermal magnetization measurements at 0.08 K and specific heat data showed that MCuV(2)O(7) exhibits antiferromagnetic long-range ordering at T(N) = 1.36 K for SrCuV(2)O(7) and T(N) = 1.47 K for BaCuV(2)O(7). Spin-flop transitions were observed in the antiferromagnetic state at 0.08 K near 0.5 kOe in SrCuV(2)O(7) and 2 kOe in BaCuV(2)O(7). In air, SrCuV(2)O(7) and BaCuV(2)O(7) melted incongruently above 983 and 1018 K, respectively.

Journal Article↗
PubMed2005

Effect of explicit cationic size and valence constraints on the phase stability of 1:2 B-site-ordered perovskite ruthenates.

The related parameters of cation size and valence that control the crystallization of Sr(3)CaRu(2)O(9) into a 1:2 B-site-ordered perovskite structure were explored by cationic substitution at the strontium and calcium sites and by the application of high pressure. At ambient pressures, Sr(3)MRu(2)O(9) stoichiometries yield multiphasic mixtures for M = Ni(2+), Mg(2+), and Y(3+), whereas pseudocubic perovskites result for M = Cu(2+) and Zn(2+). For A-site substitutions, an ordered perovskite structure results for Sr(3-x)Ca(x)CaRu(2)O(9), with 0 </= x </= 1.5. In contrast, Ba(2+) substitution for Sr(2+) is accompanied by a phase change to a hexagonal BaTiO(3) structure type. At high pressures and temperatures, a 1:2 B-site-ordered perovskite structure is stabilized for Sr(3-x)Ba(x)CaRu(2)O(9), with 0 </= x </= 3. The scarcity of B-site-ordered perovskite ruthenates at ambient pressure and the metastable nature of the high-pressure phases underscore the strict size and valence requirements that must be met by the constituent cations to achieve these uncommon ordered structures.

Journal Article↗
PubMed2004

Pressure-induced buckling of spin ladder in SrCu2O3.

Pressure-induced structural phase transition of spin ladder compound SrCu2O3 was investigated by synchrotron X-ray powder diffraction with a diamond anvil cell (DAC). The change was characterized by a buckling of the Cu2O3 plane in the rung direction of the ladder. The structure of the high-pressure phase was found to be essentially the same as that of CaCu2O3. Application of an external pressure of 3.4 GPa therefore affected the structure in the same manner that the chemical (internal) pressure does.

Journal Article↗
PubMed2004

Appraisal of surgical treatment for pT2 gallbladder carcinomas.

This retrospective study was designed to appraise the surgical procedures for pT2 gallbladder (GB) carcinomas. Twenty patients with pT2 GB carcinomas underwent surgical resection. Hepatectomy of segments 4b and 5 was performed in 19 patients, and an extended right hepatic lobectomy was performed in 1. The extrahepatic bile duct was preserved in 8 patients in whom the disease was limited to the GB fundus and/or body. Regional lymphadenectomy was performed in 18 patients. A separate radical second operation was performed in 8 patients after cholecystectomy. Final pathological staging was stage IB in 15 patients, IIB in 4, and IV in 1. Overall 5-year survival rate in those 20 patients was 77% without operative deaths. The 5-year survival rate in 5 patients with nodal metastasis and in 8 patients without extrahepatic biliary resection was 80% and 100%, respectively. A separate radical second operation in 8 patients yielded 75% survival after 5 years. Perineural invasion as a prognostic determinant was closely associated with tumor extending to the neck or the cystic duct. Partial hepatectomy, usually with extrahepatic biliary resection and regional lymphadenectomy, was appropriate as a standard radical operation for pT2 GB carcinoma, but preservation of extrahepatic bile duct is advocated for disease limited to the GB fundus and/or body. Radical second operation enhanced the chance for cure in patients with pT2 GB carcinoma.

Adult↗
PubMed2003

Short-range and long-range magnetic ordering in SrCuP2O7 and PbCuP2O7.

Magnetic properties of SrCuP2O7 and PbCu(1-x)ZnxP2O7 (x=0, 0.1, and 0.5) were studied by magnetic susceptibility, chiT, and specific heat, Cp(T). Both data showed that magnetism of SrCuP2O7 and PbCuP2O7 can be described by the one-dimensional (1D) uniform chain model despite the structural features suggesting the presence of zigzag chains with next-nearest-neighbor interactions. The chiT data were fitted by the Bonner-Fisher curve (plus temperature independent and Curie-Weiss terms) with g=2.20 and J/kB=9.38 K for SrCuP2O7 and g=2.17 and J/kB=8.41 K for PbCuP2O7 (Hamiltonian H=J SigmaSiS(i+1)). Magnetic specific heat, Cm(T), exhibited one broad maximum due to short-range ordering and one sharp peak at TN=1.64 K for SrCuP2O7 and TN=1.15 K for PbCuP2O7 due to long-range antiferromagnetic ordering. The characteristic values of the broad maxima on the Cm(T) curves (Cmax and TC(max)) were in good agreement with the theoretical calculations for the uniform 1D S=1/2 Heisenberg chain. Magnetic properties of PbCu0.9Zn0.1P2O7 still obeyed the 1D uniform chain model but those of PbCu0.5Zn0.5P2O7 did not. In air, SrCuP2O7 was stable at least up to 1373 K while PbCuP2O7 melted incongruently above 1180 K.

Journal Article↗
PubMed2003

Groin infection caused by a percutaneous femoral artery closure device: report of a case.

Hemostasis after femoral artery catheterization is generally achieved by manual compression, which results in a low incidence of infection at the puncture site. Percutaneous femoral artery closure devices have recently been used to prevent bleeding complications, shorten the hospital stay, and reduce the patient's discomfort. However, they have been associated with infectious complications, necessitating surgical intervention, such as patch angioplasty or arterial bypass; the treatment depending on the damage to the artery and the type of device used. Thus, the possibility of infection should be kept in mind when employing these devices. We report a case of groin infection associated with one such device, known as "The Closer," which was successfully treated by drainage and removal of the suture material.

Catheterization, Peripheral↗
PubMed2002

Growth of Na-doped Ca(2)CuO(2)Cl(2) single crystals under high pressures of several GPa.

Single crystals of Na-doped Ca(2)CuO(2)Cl(2) have been grown for the first time by a flux method under high pressures of up to 5.5 GPa. By changing the Na-solubility limit through the applied pressure, the Na content x was successfully controlled without introducing appreciable compositional inhomogeneity within the millimeter-sized crystals. Structural and chemical characterization indicated that the crystals span the phase diagram continuously from the parent antiferromagnetic insulator to an underdoped high-temperature superconductor. Because of the well-defined cleavage plane and resulting high surface quality, these oxychloride single crystals will provide a unique opportunity to explore the electronic evolution of the high-temperature superconductors, using spectroscopic techniques such as scanning tunneling microscopy/spectroscopy and angle-resolved photoemission spectroscopy.

Journal Article↗
PubMed2002

A novel method for the detection of Down syndrome with the use of four serum markers.

OBJECTIVE: The purpose of this study was to evaluate the use of the Lens culinaris agglutinin-reactive alpha-fetoprotein ratio for the detection of fetal Down syndrome in combination with traditional serum markers. STUDY DESIGN: We obtained maternal serum from 530 women with unaffected pregnancies and 31 women who were pregnant with a fetus with Down syndrome at 14 to 20 weeks of gestation. Various combinations of Lens culinaris agglutinin-reactive alpha-fetoprotein ratio, alpha-fetoprotein, human chorionic gonadotropin, and unconjugated estriol were evaluated by score, without regard for the maternal age-related fetal Down syndrome risk. RESULTS: The best combination of serum markers, according to our scoring method, was a combination of all 4 markers. This combination showed a sensitivity of 83.9%, with a 5.1% false-positive rate for Down syndrome. Moreover, in older women, high sensitivity was obtained without increasing the false-positive rate. CONCLUSION: The screen using all 4 markers showed high sensitivity in all age groups without increasing the false-positive rate.

Adult↗