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Katsunori Yogo,1 Masaki Misawa,2 Morihito Shimizu,2 Hidetoshi Shimizu,3 Tomoki Kitagawa,3 Ryoichi Hirayama,4 Hiromichi Ishiyama,5 Takako Furukawa,1 Hiroshi Yasuda6 1Nagoya University Graduate School of Medicine, Nagoya, Aichi, Japan; 2Health and Medical Research Institute, National Institute of Advanced Industrial Science & Technology (AIST), Tsukuba, Ibaraki, Japan; 3Department of Radiation Oncology, Aichi Cancer Center Hospital, Nagoya, Aichi, Japan; 4National Institute of Radiological Sciences (NIRS), National Institutes for Quantum and Radiological Science and Technology (QST), Chiba-shi, Chiba, Japan; 5Graduate School of Medical Science, Kitasato University, Sagamihara, Kanagawa, Japan; 6Department of Radiation Biophysics, Research Institute for Radiation Biology and Medicine, Hiroshima University, Hiroshima, JapanCorrespondence: Katsunori YogoNagoya University Graduate School of Medicine, 1-1-20 Daiko-Minami, Higashi-Ku, Nagoya, Aichi 461-8673, JapanTel +81 52 719 1103Fax +81 52 719 3172Email yogo@met.nagoya-u.ac.jpPurpose: Gold nanoparticles (AuNPs) are candidate radiosensitizers for medium-energy photon treatment, such as γ-ray radiation in high-dose-rate (HDR) brachytherapy. However, high AuNP concentrations are required for sufficient dose enhancement for clinical applications. Here, we investigated the effect of positively (+) charged AuNP radiosensitization of plasmid DNA damage induced by 192Ir γ-rays, and compared it with that of negatively (−) charged AuNPs.Methods: We observed DNA breaks and reactive oxygen species (ROS) generation in the presence of AuNPs at low concentrations. pBR322 plasmid DNA exposed to 64 ng/mL AuNPs was irradiated with 192Ir γ-rays via HDR brachytherapy. DNA breaks were detected by observing the changes in the form of the plasmid and quantified by agarose gel electrophoresis. The ROS generated by the AuNPs were measured with the fluorescent probe sensitive to ROS. The effects of positively (+) and negatively (−) charged AuNPs were compared to study the effect of surface charge on dose enhancement.Results: +AuNPs at lower concentrations promoted a comparable level of radiosensitization by producing both single-stranded breaks (SSBs) and double-stranded breaks (DSBs) than those used in cell assays and Monte Carlo simulation experiments. The dose enhancement factor (DEF) for +AuNPs was 1.3 ± 0.2 for SSBs and 1.5 ± 0.4 for DSBs. The ability of +AuNPs to augment plasmid DNA damage is due to enhanced ROS generation. While −AuNPs generated similar ROS levels, they did not cause significant DNA damage. Thus, dose enhancement using low concentrations of +AuNPs presumably occurred via DNA binding or increasing local +AuNP concentration around the DNA.Conclusion: +AuNPs at low concentrations displayed stronger radiosensitization compared to −AuNPs. Combining +AuNPs with 192Ir γ-rays in HDR brachytherapy is a candidate method for improving clinical outcomes. Future development of cancer cell-specific +AuNPs would allow their wider application for HDR brachytherapy.Keywords: gold nanoparticles, high-dose-rate brachytherapy, DNA damage, radiosensitization, 192Ir γ-rays, positively charged nanoparticles

Traditional tissue-engineered cartilage applied in clinical practice consists of cell suspensions or gel-form materials for which it is difficult to maintain their shapes. Although biodegradable polymer scaffolds are used for shape retention, deformation after transplantation can occur. Here, we showed that periostin (PN), which is abundantly expressed in fibrous tissues, contributes to the maturation and shape retention of tissue-engineered cartilage through conformational changes in collagen molecules. The tissue-engineered cartilage transplanted in an environment lacking PN exhibited irregular shapes, while transplants originating from chondrocytes lacking PN showed limited regeneration. In the in vitro assay, PN added to the culture medium of chondrocytes failed to show any effects, while the 3D culture embedded within the collagen gel premixed with PN (10 μg/mL) enhanced chondrogenesis. The PN-mediated collagen structure enhanced the mechanical strength of the surrounding fibrous tissues and activated chondrocyte extracellular signaling by interstitial fibrous tissues.

Currently, no standardized method for measuring intrahepatic fat density via conventional computed tomography (CT) exists.We aim to quantify intrahepatic fat density via material decomposition analysis using rapid kilovolt peak-switching dual-energy (RSDE) CT.Homogenized porcine liver and fat (lard) were mixed in various ratios to produce phantoms for fat density verification. The actual fat density was measured on the basis of the phantom volume and weight, and these measurements were used as reference densities. The fat and liver mass attenuation coefficients, which were used as the material basis pairs, were employed in the material decomposition analysis. Then, the measured fat density of each phantom was compared with the reference densities.For fat content differences exceeding 2%, the measured fat density for the phantoms became statistically significant (p 0.01). The correlation between the reference densities and RSDE-measured fat densities was reasonably high (R 0.9997); this indicates the validity of this analysis method.Intrahepatic fat density can be measured using the mass attenuation coefficients of fat and liver in a material decomposition analysis. Given the knowledge of the accuracy and the limitations found in this study, our method can quantitatively evaluate fat density.

In cartilage regenerative medicine, autologous chondrocyte implantation (ACI) has been applied clinically for partial defects of joint cartilage or nasal augmentation. To make treatment with ACI more effective and prevalent, modalities to evaluate the quality of transplanted constructs noninvasively are necessary. In this study, we compared the efficacy of several noninvasive modalities for evaluating the maturation of tissue-engineered auricular cartilage containing a biodegradable polymer scaffold. We first transplanted tissue-engineered cartilage consisting of human auricular chondrocytes, atelocollagen gel, and a poly-l-lactic acid (PLLA) porous scaffold subcutaneously into the back of athymic nude rats. Eight weeks after transplantation, the rats were examined by magnetic resonance imaging (MRI), X-ray, and ultrasound as noninvasive modalities. Then, the excised constructs were examined by histological and biochemical analysis including toluidine blue (TB) staining, glycosaminoglycans content, and enzyme-linked immunosorbent assay of type II collagen. Among the modalities examined, transverse relaxation time (T2) and apparent diffusion coefficient of MRI showed quite a high correlation with histological and biochemical results, suggesting that these can effectively detect the maturation of tissue-engineered auricular cartilage. Since these noninvasive modalities would realize time-course analysis of the maturation of tissue-engineered auricular cartilage, this study provides a substantial insight for improving the quality of tissue-engineered cartilage, leading to improvement of the quality and technique in cartilage regenerative medicine.

To reduce particulate matter (PM) including soot in diesel exhaust gas, a diesel particulate filter (DPF) has been developed. Since it is difficult to observe the phenomena in a DPF experimentally, we have conducted a lattice Boltzmann simulation. In this study, we simulated the flow in a metallic filter. An X-ray computed tomography (CT) technique was applied to obtain its inner structure. The processes of soot deposition and oxidation were included for a continuously regenerating diesel filter. By comparing experimental data, a parameter of soot deposition probability in the numerical model was determined.

For a development of deep tumor treatment in photodynamic therapy, a feasibility of novel radiosensitizers induced by x-ray was investigated. The sensitizers are designed to generate reactive oxygen species (ROS) inside or outside the cell, possibly leading to damage exclusively on tumor cells and reservation of normal cells along the x-ray path. Taking note of the similarity in energy transfer mechanism in photocatalysts, scintillators, and particulate semiconductors, we chose TiO2, ZnS:Ag, CeF3, and quantum dots (CdTe and CdSe) in particulate form, which contain heavy atoms for efficient absorption of x-rays. A parameter study for x-ray operating conditions showed that in a typical scenario, photons with 20 to 170 keV energy are attenuated by 90% through the region of particle dispersed aqueous solution at varying concentration between 0.01 and 100 wt%. The amount of ROS generation under the exposure of polychromatic x-ray was measured using dihydroethidium reagent which detects an integrated amount of several species. Proportional increase in ROS generation to x-ray dose was observed for varying concentrations of TiO2, ZnS:Ag, CeF3, and CdSe quantum dot dispersions. Then, HeLa cells were mixed with aqueous solutions dispersed with sensitizing materials at a concentration of 3.0 mg/ml and were exposed to x-ray. Their survival fraction obtained by a cell proliferation reagent WST-1 immediately after the irradiation showed insignificant effects of sensitizing materials except at large doses. To enhance the sensitization effect, bio-conjugated CdSe quantum dots were internalized in the cytoplasm up to a concentration of 1.0 ng/ml. The cells were irradiated by x-ray up to 5 Gy, and their survival fraction was measured by the colony forming ability 9 days after irradiation. Survival fraction of the cells treated with quantum dots were less than those without quantum dots for all doses, suggesting that the colony forming ability is impaired by the internalized quantum dots.

Since diesel exhaust gas has more ambient air pollutants such as NOx and particulate matters (PM) including soot, the special treatment for exhaust emission standards is needed. Recently, a diesel particulate filter (DPF) has been developed to reduce PM in the after-treatment of exhaust gas. However, since the structure of the filter is small and complex, it is impossible to examine the phenomena inside the filter experimentally. In this study, we conduct fluid simulation in the diesel filter. We use the lattice Boltzmann method. The soot accumulation is considered to simulate the PM trap in the filter. For the wall-boundary in the simulation, the inner structure of the filter is obtained by a 3D-CT technique. Results show complex flow pattern in the diesel filter. Due to the soot accumulation, the velocity is changed and the pressure is increased. The pressure drop becomes larger as soot concentration at the inlet is higher.

The behavior of a single bubble and a pair of bubbles under microgravity conditions has been investigated using the NASA-DC9 aircraft in order to understand the effects of various parameters and to control the bubble behavior in space. Silicone oil was used as the test liquid, and a nitrogen gas bubble was injected from the top wall under different experimental conditions. In an isothermal case, two different microgravity conditions were achieved by either fixing the experimental apparatus to the aircraft floor or freely floating the apparatus in the aircraft cabin. The bubble behavior was found to be clearly influenced by the quality of the microgravity environment, and variations of the bubble aspect ratio with the Bond number were presented. The results indicate that there is a critical Bond number of the order of 10−1 which determines the bubble shape deformation. In the free-floating experiments, a temperature gradient was imposed on the liquid around the bubble near the heated top wall. Marangoni convection was expected to occur around the bubble and the bubble behavior was studied under various temperature gradients. The bubble aspect ratio was found to decrease with an increase in the Marangoni number. A theoretical model for the relation between the Marangoni flow around the bubble and the aspect ratio is proposed based on simple assumptions. Visualization of Marangoni convection around the bubbles using the photochromic dye activation method was successfully performed. The aspect ratios predicted by the model agreed with the experimental results reasonably well. Direct measurements of surface velocity are, however, necessary to further evaluate the validity of the model.

CdZnTe (CZT) detectors are promising detectors, which have many good characteristics such as room temperature operation, reasonable energy resolution, high-detection efficiency to gamma rays, etc. However, energy resolution of CZT is governed by poor mobilities of charge carriers. Many researchers have tried to solve this problem. Among them, a clustering method has been recently proposed which is based on a digital signal processing of preamplifier output waveforms. In this method, we can classify signals according to their shapes and independently treat different shapes. In this paper, we report a new clustering algorithm with adaptive shaping time. The obtained energy resolution for /sup 137/Cs was improved to 5.4-keV full width at half maximum (FWHM) by applying this method.

A spin-density-wave (SDW) for (TMTSF)(2)PF(6) has been reported to appear below T(SDW) (=/~12 K), with a subphase transition at T* (=/~4 K). To determine the structure of the subphase, we synthesized (TMTSF)(2)PF(6), in which one side of the central carbon bond in each TMTSF molecule was replaced by (13)C, and utilized this compound in (13)C nuclear magnetic resonance measurements. Below T(SDW), the spectrum became broad and T(1)(-1) decreased, in agreement with previous results. Below T*, fine structures emerged in the center of the spectrum and T(1)(-1) decreased exponentially. These phenomena were attributed to the emergence of commensurability at T*.

5-Aminolevulinic acid (ALA) is a photosensitizer used in photodynamic therapy (PDT) because it causes preferential accumulation of protoporphyrin IX (PpIX) in tumor cells, where it forms singlet oxygen upon light irradiation and kills the tumor cells. Our previous study demonstrated that PpIX enhances generation of reactive oxygen species by physicochemical interaction with X-rays. We investigated the effect of ALA administration with X-ray irradiation of mouse B16-BL6 melanoma cells in vitro and in vivo. ALA facilitates PpIX accumulation in tumor cells and enhances ROS generation in vitro. Tumor suppression significantly improved in animals treated with fractionated doses of radiation (3 Gy × 10; total, 30 Gy) with local administration of 50 mg/kg ALA at 24 h prior to fractional irradiation. These results suggest ALA may improve the efficacy of cancer radiotherapy by acting as a radiomediator.