Mamoru Tamura

National Center for Global Health and Medicine in Japan, Edo, Tōkyō, Japan

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Publications (117)274.76 Total impact

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    ABSTRACT: A single human cell contains more than 5.0 × 10(5) copies of long interspersed element-1 (L1), 80-100 of which are competent for retrotransposition (L1-RTP). Recent observations have revealed the presence of de novo L1 insertions in various tumors, but little is known about its mechanism. Here, we found that 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 2-amino-3,8-dimethyl-imidazo[4,5-f]quinoxaline (MeIQx), food-borne carcinogens that are present in broiled meats, induced L1-RTP. This induction was dependent on a cellular cascade comprising the aryl hydrocarbon receptor (AhR), a mitogen-activated protein kinase, and CCAAT/enhancer-binding protein β. Notably, these compounds exhibited differential induction of L1-RTP. MeIQx-induced L1-RTP was dependent on AhR nuclear translocator 1 (ARNT1), a counterpart of AhR required for gene expression in response to environmental pollutants. By contrast, PhIP-induced L1-RTP did not require ARNT1 but was dependent on estrogen receptor α (ERα) and AhR repressor. In vivo studies using transgenic mice harboring the human L1 gene indicated that PhIP-induced L1-RTP was reproducibly detected in the mammary gland, which is a target organ of PhIP-induced carcinoma. Moreover, picomolar levels of each compound induced L1-RTP, which is comparable to the PhIP concentration detected in human breast milk. Data suggest that somatic cells possess machineries that induce L1-RTP in response to the carcinogenic compounds. Together with data showing that micromolar levels of heterocyclic amines (HCAs) were non-genotoxic, our observations indicate that L1-RTP by environmental compounds is a novel type of genomic instability, further suggesting that analysis of L1-RTP by HCAs is a novel approach to clarification of modes of carcinogenesis.Oncogene advance online publication, 3 December 2012; doi:10.1038/onc.2012.516.
    Oncogene 12/2012; · 7.36 Impact Factor
  • Advances in experimental medicine and biology 01/2012; 737:19-24. · 1.83 Impact Factor
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    ABSTRACT: Near-infrared spectroscopy (NIRS) is a cerebral monitoring method that noninvasively and continuously measures cerebral hemoglobin oxygenation and the redox state of cytochrome oxidase using highly tissue-permeable near-infrared light. This technique now has wide clinical application, and its usefulness in the measurement of cerebral hemoglobin oxygenation has been confirmed under global cerebral injury and/or hypoxemic hypoxia; however, regional cerebral infarction located far from the monitoring site may not be detected by NIRS. Furthermore, the specificity and accuracy of the measurement of the redox state of cytochrome oxidase remain controversial. We apply NIRS to both animal and clinical investigations. Based on these results, we discuss the significance of the measurement of cerebral hemoglobin oxygenation and cytochrome oxidase in vivo and in clinical medicine. Using our algorithm, cytochrome oxidase signals are unaffected by hemoglobin signals, even when hematocrit values change from 35 to 5% under cardiopulmonary bypass in a dog model. In the clinical study, cytochrome oxidase during surgery is likely to be a good (though not perfect) predictor of postoperative cerebral outcome. NIRS appears to be a promising technology, but additional investigations are required to establish its clinical efficacy and justify its routine use during operative and perioperative periods.
    Journal of Biomedical Optics 01/2008; 13(3):033001. · 2.88 Impact Factor
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    ABSTRACT: Fluorescence correlation spectroscopy (FCS) and fluorescence cross-correlation spectroscopy (FCCS) are powerful techniques to measure molecular interactions with high sensitivity in homogeneous solution and living cells. In this study, we developed methods for the detection of prion protein (PrP) using FCS and FCCS. A combination of a fluorescent-labeled Fab' fragment and another anti-PrP monoclonal antibody (mAb) enabled us to detect recombinant bovine PrP (rBoPrP) using FCS because there was a significant difference in the diffusion coefficients between the labeled Fab' fragment and the trimeric immune complex consisting of rBoPrP, labeled Fab' fragment, and another anti-PrP mAb. On the other hand, FCCS detected rBoPrP using two mAbs labeled with different fluorescence dyes. The detection limit for PrP in FCCS was approximately threefold higher than that in FCS. The sensitivity of FCCS in detection of abnormal isoform of PrP (PrP(Sc)) was comparable to that of enzyme-linked immunosorbent assay (ELISA). Because FCS and FCCS detect the PrP immune complex in homogeneous solution of only microliter samples with a single mixing step and without any washing steps, these features of measurement may facilitate automating bovine spongiform encephalopathy diagnosis.
    Analytical Biochemistry 12/2007; 370(2):131-41. · 2.58 Impact Factor
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    Goro Nishimura, Chan-Gi Pack, Mamoru Tamura
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    ABSTRACT: In this paper, we report on phosphorescence measurements for oxygen dynamics in cells by means of a correlation method, which is an expansion of the fluorescence correlation spectroscopy. The intensity correlation function of the emission excited by a pulsed light source was measured. With changing the pulse timing, both the fluorescence correlation function and the decay time of phosphorescence could be analyzed. This method was applied for the analysis of the oxygen dynamics in HeLa cells stained by Pd(II)-porphine. The decay function consisted of two exponential components, which might be attributed to free and protein-bound forms of Pd(II)-porphine in the cell, respectively. The relative change of the oxygen concentration under normal and uncoupled respiration conditions was also measured. The simplicity of this method is a great advantage in the biological applications. Although the current system we used was limited in the temporal resolution, the method is in principle applicable to faster decay time measurements down to the nano-second range of the fluorescence decay times.
    Experimental and Molecular Pathology 05/2007; 82(2):175-83. · 2.13 Impact Factor
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    ABSTRACT: The diffusion properties of hGRalpha in living cells have been analyzed. The hGRalpha translocalized from the cytosol to the nucleus after addition of Dex just as RU486; however, the Brownian motions of the proteins in nucleus were different. In order to analysis microenvironment of the nucleus of living cell, four different tandem EGFPs were constructed. Diffusion of tandem EGFP was dependent on the length of the protein as a rod-like molecule in solution. We found two kinds of mobility, fast diffusional mobility as a major component and much slower diffusional mobility as a major component in living cells nucleoplasm. On the bases of this analysis, we compared the diffusion property of hGRalpha in the nucleus at the presence of Dex or RU486 by distribution of diffusion constants. Our result may suggest that EGFP-hGRalpha is activated by RU486 and kept the stage of binding cofactor, GRE and final complex. Finally this means that dimerization is not required for association with GRE, although it is required for stabilization of a complex of EGFP-hGRalpha.
    Experimental and Molecular Pathology 05/2007; 82(2):163-8. · 2.13 Impact Factor
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    ABSTRACT: The diffusion properties of EGFP-hGRalpha and mutants C421G, A458T and I566 in living cells were analyzed. The wild type and mutants C421G and A458T translocated from the cytoplasm to the nucleus after addition of Dex; however, the Brownian motions of the proteins were different. The diffusion constant of wild-type GRalpha after addition of Dex slowed to 15.6% of that in the absence of Dex, whereas those of A458T and C421G slowed to 34.8% and 61.7%, respectively. This is the first report that dimer formation is less important than the binding activity of GRalpha to GRE in the living cell.
    FEBS Letters 03/2007; 581(3):389-93. · 3.58 Impact Factor
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    ABSTRACT: We developed a three-wavelength time-resolved spectroscopy (TRS) system, which allows quantitative measurement of hemodynamics within relatively large living tissue. We clinically evaluated this TRS system by monitoring cerebral circulation during cardiopulmonary bypass surgery. Oxyhemoglobin, deoxyhemoglobin, total hemoglobin and oxygen saturation (SO(2)) were determined by TRS on the left forehead attached with an optode spacing of 4 cm. We also simultaneously monitored jugular venous oxygen saturation (SjvO(2)) and arterial blood hematocrit (Hct) using conventional methods. The validity and usefulness of the TRS system were assessed by comparing parameters obtained with the TRS and conventional methods. Although the changes in SO(2) were lower than those in SjvO(2), SO(2) obtained by TRS paralleled the fluctuations in SjvO(2), and a good correlation between these values was observed. The only exceptions occurred during the perfusion period. Moreover, there was a good correlation between tHb and Hct values (r(2)=0.63). We concluded that time-resolved spectroscopy reflected the conditions of cerebral hemodynamics of patients during surgical operations.
    Journal of Biomedical Optics 01/2007; 12(6):062112. · 2.88 Impact Factor
  • Goro Nishimura, Changi Pack, Mamoru Tamura
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    ABSTRACT: We report on a simple correlation method for lifetime measurements using a random modulated excitation light source. We use an intensity correlation function of emission for lifetime analyses. In this method, no reference timing of the excitation is required. We apply the correlation method to measure phosphorescence decays and successfully demonstrate in the analysis of the phosphorescence decay from Pd(II) porphine in HeLa cells under aerobic and anaerobic conditions to understand the oxygen dynamics in individual cells. The method is applicable to faster decay time measurements down to a nanosecond range when the detection system is improved. Current fluorescence correlation setups can easily be modified for lifetime measurements, expanding the applicability in biological problems.
    Journal of Biomedical Optics 01/2007; 12(2):020503. · 2.88 Impact Factor
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    ABSTRACT: Four different tandem EGFPs were constructed to elucidate the nuclear microenvironment by quantifying its diffusional properties in both aqueous solution and the nuclei of living cells. Diffusion of tandem EGFP was dependent on the length of the protein as a rod-like molecule or molecular ruler in solution. On the other hand, we found two kinds of mobility, fast diffusional mobility and much slower diffusional mobility depending on cellular compartments in living cells. Diffusion in the cytoplasm and the nucleoplasm was mainly measured as fast diffusional mobility. In contrast, diffusion in the nucleolus was complex and mainly much slower diffusional mobility, although both the fast and the slow diffusional mobilities were dependent on the protein length. Interestingly, we found that diffusion in the nucleolus was clearly changed by energy depletion, even though the diffusion in the cytoplasm and the nucleoplasm was not changed. Our results suggest that the nucleolar microenvironment is sensitive to energy depletion and very different from the nucleoplasm.
    Biophysical Journal 12/2006; 91(10):3921-36. · 3.67 Impact Factor
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    ABSTRACT: Total internal reflection fluorescence correlation spectroscopy (TIR-FCS) allows us to measure diffusion constants and the number of fluorescent molecules in a small area of an evanescent field generated on the objective of a microscope. The application of TIR-FCS makes possible the characterization of reversible association and dissociation rates between fluorescent ligands and their receptors in supported phospholipid bilayers. Here, for the first time, we extend TIR-FCS to a cellular application for measuring the lateral diffusion of a membrane-binding fluorescent protein, farnesylated EGFP, on the plasma membranes of cultured HeLa and COS7 cells. We detected two kinds of diffusional motion-fast three-dimensional diffusion (D(1)) and much slower two-dimensional diffusion (D(2)), simultaneously. Conventional FCS and single-molecule tracking confirmed that D(1) was free diffusion of farnesylated EGFP close to the plasma membrane in cytosol and D(2) was lateral diffusion in the plasma membrane. These results suggest that TIR-FCS is a powerful technique to monitor movement of membrane-localized molecules and membrane dynamics in living cells.
    Biophysical Journal 12/2006; 91(9):3456-64. · 3.67 Impact Factor
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    Goro Nishimura, Ikuhiro Kida, Mamoru Tamura
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    ABSTRACT: Time- and space-resolved diffuse reflectance measurements were used to identify the optical parameters, the reduced scattering and absorption coefficients, of bulk living tissue in the region from 1.15 to 1.52 microm. Although in this region the detector was limited in its temporal resolution, we applied a peak-time shift analysis successfully to determine these coefficients in a human forearm, and then determined the absorption spectrum by space-resolved diffuse reflectance measurements. The absorption spectrum of a water content of 52% determined by magnetic resonance imaging experiments is in good agreement with the absorption coefficient obtained by optical measurements. Moreover, magnetic resonance imaging measurements suggest that the deviation of the absorption coefficients from the water spectrum in the strong water absorption band is caused by the heterogeneity of water distribution in tissue: the low content of water in the skin. These findings indicate that this optical method is potentially applicable to the non-invasive measurement of water in tissue, especially in a region lower than about 1.3-1.35 microm, which may be useful in monitoring oedema and tissue swelling.
    Physics in Medicine and Biology 07/2006; 51(11):2997-3011. · 2.70 Impact Factor
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    ABSTRACT: Water-soluble CdSe/ZnS (core-shell) semiconductor quantum dots surface-modified with tetrahexyl ether derivatives of p-sulfonatocalix[4]arene were synthesized for the optical detection of the neurotransmitter acetylcholine.
    Chemical Communications 10/2005; · 6.38 Impact Factor
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    ABSTRACT: Recent experimental studies have shown that bone marrow stromal cells (BMSC) differentiate into neural cells and reduce neurological deficits when transplanted into traumatized spinal cord. These findings have been derived primarily from histological analyses. We conducted a study directed chiefly at developing a non-invasive system for tracking BMSC transplanted into the spinal cord of living animals. In this study, we induced spinal cord injury (SCI) in rats with a pneumatic device. BMSC were harvested from transgenic mice expressing green fluorescence protein (BMSC-GFP), and were transplanted stereotactically into a control group of rats without SCI (n = 6) and a group with SCI (n = 3). At 2 and 4 weeks after transplantation, the dura mater was exposed and green fluorescence derived from the transplanted BMSC-GFP was observed. The distribution and differentiation of the transplanted cells were subsequently evaluated with immunohistochemistry. Green fluorescence could be detected around the transplantation site in three of six of the control rats. In all three rats subjected to SCI, green fluorescence was shown to spread from the site of BMSC-GFP injection toward the injury site, suggesting that the transplanted cells had migrated toward the lesion within the 4-week post-transplantation period. Histological evaluation suggested that the detected green fluorescence was emitted by cells that had distributed in the dorsal white matter, and demonstrated that some of the transplanted cells expressed neuronal or astrocytic markers. These results suggest the possibility of tracking BMSC transplanted into the spinal cord in living animals. Such noninvasive bioimaging techniques would be valuable for monitoring the fate of these transplanted cells and assessing the safety and efficacy of their transplantation.
    Journal of Neurotrauma 09/2005; 22(8):907-18. · 4.30 Impact Factor
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    ABSTRACT: Single-molecule fluorescence methods enable a new class of nucleic acid assays to be performed that are not possible with PCR-based methods. In this basic study, the methylene tetrahydrofolate reductase (MTHFR)-genotypes (normal, homozygous mutated, as well as heterozygous mutated) were directly detected for the first time onto unamplified double-stranded genomic DNA in solution down to femtomolar allele concentrations (10(-15) M) in a homogeneous assay format. This was accomplished by taking advantage of the decrease by a factor of 40 to 100 in fluorescence background signals of the non-bound nonlinear hybridization probes in two colors and two-color fluorescence cross-correlation spectroscopy. The designed 'intelligent' probes contained the built-in 5'-fluorescent dyes rhodamine green and Alexa633, respectively, and the 3'-non-fluorescent quenchers BHQ1 and BHQ3, respectively, with perfectly matched spectral overlaps for both dye-quencher combinations. Upon binding of two appropriate probes that were sequence-specific for the genotype, the steady-state fluorescence in two colors increased by about two orders of magnitude. The obtained allele sensitivity of femtomolar and the specificity of the described molecular interactions allow PCR-based allele distinction to be circumvented. Furthermore, the results present an alternative to existing hybridization approaches that are currently used with and without amplification at the 'many-molecule' level and the 'single-molecule' level.
    Experimental and Molecular Pathology 07/2005; 78(3):177-89. · 2.13 Impact Factor
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    ABSTRACT: A simple method for the preparation of highly fluorescent and stable, water-soluble CdSe-ZnS quantum dots is reported using calix[4]arene carboxylic acids as surface coating agents; the coating of the surface with the calixarene and the conjugation of antibodies to the quantum dots are confirmed by fluorescence correlation spectroscopy.
    Chemical Communications 07/2005; · 6.38 Impact Factor
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    Goro Nishimura, Mamoru Tamura
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    ABSTRACT: The least-squares (LS) method in fluorescence decay analyses and in time-domain analyses of the diffuse scattering light for data measured by the time-correlated single photon counting (TCSPC) technique is experimentally evaluated, and the artefact in LS analysis for data with different counting statistics is discussed. In single exponential decay analysis, the error of the decay parameter by the LS method is smaller than 10% of the expected true value when the average number of counts per bin (N/k) is more than 1, and the fitting region covers a period on the order of the decay time. In multi-exponential analysis, the decay parameters are sensitively dependent on the counting statistics. In contrast, the fitting by the maximum likelihood estimation (MLE), assuming Poissonian statistics, greatly reduces such dependence of parameters on the counting statistics. In another application, time-domain diffuse scattering measurements, the LS method is only accurate at N/k > 50 (10% error in the absorption coefficient). In particular, the absorption coefficient is largely dependent on the count. In both examples, the problem of stability in the fitting process by MLE still remains: the convergence of the fitting is critically dependent on the selection of initial guesses of the parameters in contrast to the convergence in the LS method. Thus, a hybrid method using the LS method for the determination of the initial guesses is a practical solution to this problem.
    Physics in Medicine and Biology 03/2005; 50(6):1327-42. · 2.70 Impact Factor
  • G Nishimura, M Tamura
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    ABSTRACT: The time-of-flight (TOF) method and the diffuse reflectance (DR) method were applied for the characterization of optical parameters in living tissue in the region of 1-2 μm. The absorption coefficient obtained by the TOF method was consistent with the content of water in the tissue. The DR measurement indicates the very large attenuation in the wavelength region above 1.4 μm. In this region, it is suggested that the optical transport does not diffuse well and it is localized at the light source.
    Biophotonics, 2004. APBP 2004. The Second Asian and Pacific Rim Symposium on; 01/2005
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    Goro Nishimura, Mamoru Tamura
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    ABSTRACT: Analysis of time-of-flight (TOF) data is sometimes limited by the instrumental response function, and optical parameters are extracted from the observed response curve by several mathematical methods, such as deconvolution. In contrast to this, we demonstrate that a method using shifts of the peak time of the response curve with different source-detector separations can yield the average path length of the light traveling in a tissue-like sample without deconvolution. In addition, combining the intensity information allows us to separate the scattering and absorption coefficients. This simple method is more robust in signal-to-noise ratio than the moment analysis, which also does not require the deconvolution procedure, because the peak position is not significantly dependent on the baseline fluctuation and the contamination of the scattering. The analysis is demonstrated by TOF measurements of an Intralipid solution at 800 nm, and is applied to the measurements at 1.29 microm, where the temporal response of photomultiplier tubes is not sufficiently good.
    Journal of Biomedical Optics 01/2005; 10(1):14016. · 2.88 Impact Factor
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Publication Stats

2k Citations
274.76 Total Impact Points

Institutions

  • 2012
    • National Center for Global Health and Medicine in Japan
      Edo, Tōkyō, Japan
  • 2002–2012
    • Kagoshima University
      • Department of Anesthesiology and Critical Care Medicine
      Kagosima, Kagoshima, Japan
  • 2007
    • Daiwa House Central Research Laboratory
      Edo, Tōkyō, Japan
  • 1987–2007
    • Hokkaido University
      • • Laboratory of Biophysics
      • • Research Institute for Electronic Science
      • • Health Administration Center
      Sapporo-shi, Hokkaido, Japan
  • 2003
    • Yamagata University
      • Faculty of Engineering
      Ямагата, Yamagata, Japan
  • 1996–2001
    • Hokkaido University Hospital
      • Division of Neurosurgery
      Sapporo, Hokkaidō, Japan
    • HAMAMATSU Photonics K.K.
      Hamamatu, Shizuoka, Japan
  • 1998
    • Setsunan University
      • Faculty of Pharmaceutical Sciences
      Ōsaka-shi, Osaka-fu, Japan
    • China-Japan Friendship Hospital
      Peping, Beijing, China
  • 1994
    • Osaka Bioscience Institute
      Ōsaka, Ōsaka, Japan
  • 1988
    • Shimizu Corporation
      Тояма, Toyama, Japan
    • University of Pennsylvania
      • Department of Medicine
      Philadelphia, PA, United States