Effects of Molecular Weight and Ionic Strength on the Adsorbing Dynamics of Polyelelectrolyte Chains onto Colloidal Particles(Poster session 1, New Frontiers in Colloidal Physics : A Bridge between Micro- and Macroscopic Concepts in Soft Matter)

この論文は国立情報学研究所の電子図書館事業により電子化されました。高分子電解質はコロイド粒子表面に吸着し架橋作用を出現させるため、コロイドの凝集剤として広く用いられているが、溶液中の高分子鎖がどのようにしてコロイド粒子表面へ吸着し、架橋作用を出現させるか、その機構の動力学は十分明らかではない.その機構にアプローチするために、ここでは裸のコロイド粒子に粒子と反対符号の荷電を持つ高分子電解質を吸着させていったときの電気泳動移動度の変化を経過時間の関数としてモニターした。その結果、イオン強度が低く、高分子の分子量が大きいとき、吸着時の緩和速度が著しく低下することが見出された

Determination of the Rate of Salt-Induced Rapid Coagulation of Polystyrene Latex Particles in Turbulent Flow Using Small Stirred Vessel

In our study, we revisited a previously reported method for evaluating the mixing intensity of uniform colloidal spheres in terms of their collision frequency, with the aim of evaluating the validity of this method in the case of a small stirred vessel equipped with an impeller with four paddles. The rates of the salt-induced rapid coagulation of polystyrene latex (PSL) particles with five different diameters were measured as functions of the rotation rate. The ad-hoc assumption of the linear additivity of the perikinetics and the orthokinetics of the coagulation process was used for the analysis. Our previously proposed equation for the rate of turbulent coagulation as a function of the particle diameter, determined for an end-over-end rotation mixing device, was confirmed to be valid. However, it was found that, for small particles and low-mixing rates, i.e., for low Peclet numbers, the rate of coagulation becomes larger than that predicted on the basis of linear additivity because of the coupling effect of Brownian motion and the fluid flow during turbulent mixing. This increase occurred even though the rate was lowered by the wall effect, which resulted in an inhomogeneous distribution of the mixing intensity

Inhibition of Cationic Polymer-Induced Colloid Flocculation by Polyacrylic Acid

Although the dosage of cationic flocculants used for water treatment is well known to increase in the presence of natural organic matter (NOM), the underlying reasons for this increase are not properly understood. Herein, we studied the flocculation behavior of polystyrene latex (PSL) particles in the presence and absence of polyacrylic acid (PAA5K) as an NOM analogue using an end-over-end rotation apparatus for standardized flow mixing. In the absence of PAA5K, the initial rate of cationic flocculant (PAM5M)-induced flocculation was enhanced, as reflected by the size of flocculant in solution. Additionally, flocculation experiments were performed in the presence of 0.5 mg/L PAA5K for five concentrations of PAM5M and two ionic strengths, and the increase of the initial rate of PAM5M-induced flocculation was suppressed by PAA5K immediately after mixing, with the most pronounced suppression obtained at a PAM5M concentration similar to PAA5K. Based on the above insights and the results of viscosity measurements, the inhibitory effect of PAA on flocculation was ascribed to (1) the reduction of PAM charge and the concomitant shrinkage via electrostatic association with PAA and (2) the termination of polycation adsorption on PSL caused by polyion complex formation when the charge ratio of PAM:PAA is close to unity

Effects of nanobubble water on the growth of Lactobacillus acidophilus 1028 and its lactic acid production

Nanobubble water (NBW) has been applied in various fields due to the unique properties of nanobubbles (NBs) including long-term stability, negative zeta potential and generation of free radicals. In this study, the performance of four kinds of NBW from different gases (air, N2, H2, and CO2) in addition to deionized water (DW) were investigated and compared in terms of the growth of the probiotic Lactobacillus acidophilus 1028. The NB density, size distribution, zeta potential, pH and dissolved oxygen (DO) of the NBW were firstly investigated. Results indicate that N2-NBW had the highest absolute value of zeta potential and NB density (−25.3 ± 5.43 mV and 5.73 ± 1.0 × 107 particles per mL, respectively), while the lowest was detected in CO2-NBW (−6.96 ± 2.36 mV and 3.39 ± 1.73 × 107 particles per mL, respectively). With the exception of CO2-NBW, all the other types of NBW showed promotion effects on the growth of the strain at the lag and logarithmic phases. Among them, N2-NBW demonstrated the best performance, achieving the highest increase ratio of 51.1% after 6 h cultivation. The kinetic models (Logistic and Gompertz) indicate that the culture with N2-NBW had the shortest lag phase and the maximum specific growth rate when compared to the H2-NBW and DW groups under the same cultivation conditions. Preliminary analysis on the mechanisms suggested that these effects were related to the properties (zeta potential and density) of the NBs, which might affect the transport of substances. This study suggests that NBW has the potential for promoting the production efficiency of probiotics via fermentation

In Vivo Simultaneous Imaging of Vascular Pool and Hypoxia with a HT-29 Tumor Model: the Application of Dual-Isotope SPECT/PET/CT

Investigation of vascularity and hypoxia in tumors is important in understanding cancer biology to developthe therapeutic strategies in cancer treatment. ------------------------------------------------------------------------ *Corresponding author . Recently, an imaging technology with the VECTor SPECT/PET/CT small-animal scanner (MILabs) has been developed to obtain simultaneous images usingtwodifferent tracers labeled with SPECT and PET nuclides, respectively. In this study, we developed amethod to simultaneously visualize vascularity and hypoxia witha human colon carcinoma HT-29tumor-bearing mouse model with 99mTc-labeled human serum albumin (99mTc-HSA) to detect blood pool, and 64Cu-diacetyl-bis (N4-methylthiosemicarbazone) (64Cu-ATSM) to detect the over-reduced conditionsunder hypoxia, by applying this SPECT/PET/CT technology.Prior to the in vivo experiments, a phantom study was conducted to confirmquantitativity of the 99mTc/64Cu dual-isotope imaging with the SPECT/PET/CT system,by comparing radioactivities detected by SPECT/PET/CT system and those of standards under the conditions of wide range of radioactivities and various content ratios, in our settings. An in vivoimaging study was conducted with HT-29 tumor-bearing mice. Both 64Cu-ATSM (37 MBq) and 99mTc-HSA (18.5 MBq) were intravenously injected into a mouse (n = 4) at 1 h and 10 min, respectively, before scanning for 20 min; the 99mTc/64Cu dual-isotope SPECT/PET/CT images were then obtained.The phantom study demonstrated that this system has high quantitativity, even when 2 isotopes co-existed and the content ratio was changed over a wide range, indicating the feasibility for in vivo experiments. In vivoSPECT/PET/CT imaging with 64Cu-ATSM and 99mTc-HSA visualized the distribution of each probe and showed that 64Cu-ATSM high-uptake regions barely overlapped with 99mTc-HSA high-uptake regions within HT-29 tumors.We developed a method to simultaneously visualize vascularity and hypoxia within HT-29tumors using in vivodual-isotope SPECT/PET/CT imaging. This methodology would be useful for studies oncancer biology with mouse tumor models anddevelopment of the treatment strategies against cancer. Examination of vascularity and hypoxia within in vivotumors is important in understanding the biology of cancer anddevelopmentof the therapeutic strategies in cancer treatment. For hypervascular tumors, antiangiogenic therapy and antivascular therapy are promising approaches. For antiangiogenic therapy, the anti-vascular endothelial growth factor antibody bevacizumab is now clinically used worldwide [1-4], and for antivascular therapy, a clinical trial withcombrestatin A4 phosphate is conducted[5]. For hypovascular tumor, which is usually associated with hypoxia, intensive treatment is necessary, since tumor hypoxia is reportedly resistant to chemotherapy and radiotherapy [6-8]. In recent years, several therapeutic methods have been proposedto damage to hypoxic regions within tumors, such as intensity modulated radiation therapy with hypoxia positron emission tomography (PET) imaging [9, 10], and carbon-ion radiotherapy, which is able to damage tumor cells even in the absence of oxygen by high linear energy transfer beam [11, 12]. However, considering the difficulty of cancer radical cure at the present moment, more effective drugs and treatment methods for antiangiogenic, antivascular, and antihypoxia therapies need to be developed. In addition, combinations of these therapies would be effective approaches, since they can attacktumor vascularity and hypoxia closely linked each other.However, it is still difficult to observe tumor vascularity and hypoxia both coincidently and concisely in in vivo tumor-bearing mouse model. Recently, a technology of single-photon emission computed tomography/positron emission tomography/computed tomography(SPECT/PET/CT) imaging with the VECTor small-animal scanner, launched from MILabs (Utrecht, Netherlands), has been reportedto obtain truly simultaneous images with twotracers labeled with SPECT and PET nuclides, respectively. Conventionally, dual-isotope imaging studies with SPECT and PET have been performed by obtaining each image independently with 2 separate systems [13, 14]. In contrast, the VECTor system is equipped with a clustered pinhole collimator, which dramatically reduces pinhole-edge penetration of high-energy annihilation ?-photons from PET nuclides and enables it to detect high-energy ?-photons derived from PET nuclides, in a manner similar to SPECT nuclides, and to obtain high-resolution images from positron emitters and single-photon emitters at the same time by separating the images based on the photon energy [15, 16]. Thus, this system has a novel concept to make images of PET nuclides, compared to the typical PET system, which measures the coincidence of annihilation ?-photons. Goorden et al. have reported that this system shows high spatial resolution, with 0.8 mm for PET nuclides and 0.5 mm for SPECT nuclides [15]. Miwa et al. also confirmed its performance in simultaneous detection of 99mTc and 18F using this system [17]. In this study, we developed a methodology to easily observe intratumoralvascularity and hypoxia in a simultaneous manner,by applyingthis SPECT/PET/CT technology. We used 99mTc-labeled human serum albumin (99mTc-HSA) labeled with a SPECT nuclide 99mTc (half-life = 6.0 h; 140 keV ?-ray: 89%) to visualize tumor vascularity by detecting blood pool [18]. The 99mTc-HSAhas been reported to detect tumor blood pool in many types of cancer, including colon cancer, renal cell carcinoma, and liver tumor in both preclinical and clinical studies [19-21]. We also used 64Cu-diacetyl-bis (N4-methylthiosemicarbazone) (64Cu-ATSM), labeled with a PET nuclide 64Cu (half-life = 12.7 h; ?+-decay: 17.4%; ??-decay: 38.5%; and electron capture: 43%) [22], to detect tumor hypoxia. The Cu-ATSM, labeled with Cu radioisotopes, such as 60Cu, 62Cu, and 64Cu, has been developed as an imaging agent targeting hypoxic regions in tumors for use with PET [23-26].Many studies have demonstrated that Cu-ATSM accumulation is associated with hypoxic conditions of tumor in vitro and in vivo[26-29]. The mechanism of radiolabeled Cu-ATSM accumulation has been studied: Cu-ATSM has small molecular sizeand high membrane permeability, and thus rapidly diffuses into cells and is reduced and trapped within cells under highly reduced intracellular conditions such as hypoxia [24, 29-31]. A clinical study with 62Cu-ATSM demonstrated that high levels of hypoxia-inducible factor-1? (HIF-1?) expression were found in Cu-ATSM uptake regions in the tumors of patients with glioma [32]. In this study, we performed simultaneous in vivo imaging using a SPECT/PET/CT with 99mTc-HSA and 64Cu-ATSM for detecting tumor vascularity and hypoxia with a HT-29 tumor-bearing mouse model

Oxidative Stress Impairs the Heat Stress Response and Delays Unfolded Protein Recovery

Background: Environmental changes, air pollution and ozone depletion are increasing oxidative stress, and global warming threatens health by heat stress. We now face a high risk of simultaneous exposure to heat and oxidative stress. However, there have been few studies investigating their combined adverse effects on cell viability. Principal Findings: Pretreatment of hydrogen peroxide (H2O2) specifically and highly sensitized cells to heat stress, and enhanced loss of mitochondrial membrane potential. H 2O 2 exposure impaired the HSP40/HSP70 induction as heat shock response (HSR) and the unfolded protein recovery, and enhanced eIF2a phosphorylation and/or XBP1 splicing, land marks of ER stress. These H2O2-mediated effects mimicked enhanced heat sensitivity in HSF1 knockdown or knockout cells. Importantly, thermal preconditioning blocked H 2O 2–mediated inhibitory effects on refolding activity and rescued HSF1 +/+ MEFs, but neither blocked the effects nor rescued HSF1-/- MEFs. These data strongly suggest that inhibition of HSR and refolding activity is crucial for H2O2–mediated enhanced heat sensitivity. Conclusions: H2O2 blocks HSR and refolding activity under heat stress, thereby leading to insufficient quality control and enhancing ER stress. These uncontrolled stress responses may enhance cell death. Our data thus highlight oxidative stres

Study of the cell cycle-dependent assembly of the DNA pre-replication centres in <i>Xenopus</i> egg extracts

RPA is a cellular, three‐subunit, single‐stranded (ss) DNA binding protein, which assists T‐antigen in the assembly of the pre‐priming complex in the SV40 replication system. By immunodepletion and complementation, we have identified RPA as an essential factor for cellular DNA replication in Xenopus extracts. RPA assembles post‐mitotically on the decondensing chromosomes into numerous subnuclear pre‐replication centres (preRCs) which serve, upon formation of the nuclear membrane, as RCs for the initiation of DNA synthesis. By a variety of experiments including the use of isolated components, we demonstrate that an inactive cdc2‐cyclin B kinase complex is essential to allow post‐mitotic assembly of the preRCs. In contrast, the active cdk2‐cyclin A kinase does not impede or facilitate the assembly of preRCs. Digestion analysis using the single‐strand‐specific P1 nuclease as well as competition experiments with ssDNA, reveal that replication‐associated unwinding of the DNA, assisted by RPA, requires the formation of the nuclear membrane. The p21 cdk‐interacting protein Cip1 appears to inhibit DNA replication prior to the unwinding DNA step, but after assembly of preRC and nuclear reconstruction