Onset of catalytic activity of gold clusters on titania with the appearance of nonmetallic properties

Gold clusters ranging in diameter from 1 to 6 nanometers have been prepared on single crystalline surfaces of titania in ultrahigh vacuum to investigate the unusual size dependence of the low-temperature catalytic oxidation of carbon monoxide. Scanning tunneling microscopy/spectroscopy (STM/STS) and elevated pressure reaction kinetics measurements show that the structure sensitivity of this reaction on gold clusters supported on titania is related to a quantum size effect with respect to the thickness of the gold islands; islands with two layers of gold are most effective for catalyzing the oxidation of carbon monoxide. These results suggest that supported clusters, in general, may have unusual catalytic properties as one dimension of the cluster becomes smaller than three atomic spacings.

Present-day crustal deformation in China constrained by global positioning system measurements

Global Positioning System (GPS) measurements in China indicate that crustal shortening accommodates most of India's penetration into Eurasia. Deformation within the Tibetan Plateau and its margins, the Himalaya, the Altyn Tagh, and the Qilian Shan, absorbs more than 90% of the relative motion between the Indian and Eurasian plates. Internal shortening of the Tibetan plateau itself accounts for more than one-third of the total convergence. However, the Tibetan plateau south of the Kunlun and Ganzi-Mani faults is moving eastward relative to both India and Eurasia. This movement is accommodated through rotation of material around the eastern Syntaxis. The North China and South China blocks, east of the Tibetan Plateau, move coherently east-southeastward at rates of 2 to 8 millimeters per year and 6 to 11 millimeters per year, respectively, with respect to the stable Eurasia.

Harmonic hepatic US with microbubble contrast agent: initial experience showing improved characterization of hemangioma, hepatocellular carcinoma, and metastasis

PURPOSE

To characterize blood flow in focal hepatic lesions with harmonic ultrasonographic (US) imaging and a microbubble contrast agent.

MATERIALS AND METHODS

Thirty patients with known hepatic masses were examined after injection of a perfluorocarbon microbubble agent. Tumor vascularity was assessed with continuous, harmonic gray-scale imaging with a low mechanical index (MI). Tumor vascular volume was assessed with brief, high-MI insonation called interval-delay imaging, which caused microbubble destruction. As the total contrast agent volume in the liver reflects the total vascular volume, quantitation of lesion enhancement relative to normal hepatic enhancement helped determine the vascular volume of the tumor relative to that of normal parenchyma.

RESULTS

Low-MI continuous harmonic imaging showed lesional vessels in hepatocellular carcinomas, minimal or no vessels in hemangiomas, and variable vascularization in metastases. High-MI interval-delay imaging showed greater enhancement in hepatocellular carcinomas than in normal liver (P <.02) and showed less enhancement in hemangiomas than in normal liver (P <.02). Enhancement in metastases was greater in the margins than in the center; as a result, the lesions appeared smaller (P <.03) and less well defined on the interval-delay images.

CONCLUSION

Contrast-enhanced harmonic imaging appears superior to conventional Doppler US for hepatic mass characterization. Low-MI continuous and high-MI interval-delay imaging can help assess tumor vascular pattern and microvascular volume.

Metabolic engineering of bacteria for ethanol production

Technologies are available which will allow the conversion of lignocellulose into fuel ethanol using genetically engineered bacteria. Assembling these into a cost-effective process remains a challenge. Our work has focused primarily on the genetic engineering of enteric bacteria using a portable ethanol production pathway. Genes encoding Zymomonas mobilis pyruvate decarboxylase and alcohol dehydrogenase have been integrated into the chromosome of Escherichia coli B to produce strain KO11 for the fermentation of hemicellulose-derived syrups. This organism can efficiently ferment all hexose and pentose sugars present in the polymers of hemicellulose. Klebsiella oxytoca M5A1 has been genetically engineered in a similar manner to produce strain P2 for ethanol production from cellulose. This organism has the native ability to ferment cellobiose and cellotriose, eliminating the need for one class of cellulase enzymes. The optimal pH for cellulose fermentation with this organism (pH 5.0-5.5) is near that of fungal cellulases. The general approach for the genetic engineering of new biocatalysts has been most successful with enteric bacteria thus far. However, this approach may also prove useful with Gram-positive bacteria which have other important traits for lignocellulose conversion. Many opportunities remain for further improvements in the biomass to ethanol processes. These include the development of enzyme-based systems which eliminate the need for dilute acid hydrolysis or other pretreatments, improvements in existing pretreatments for enzymatic hydrolysis, process improvements to increase the effective use of cellulase and hemicellulase enzymes, improvements in rates of ethanol production, decreased nutrient costs, increases in ethanol concentrations achieved in biomass beers, increased resistance of the biocatalysts to lignocellulosic-derived toxins, etc. To be useful, each of these improvements must result in a decrease in the cost for ethanol production. Copyright 1998 John Wiley & Sons, Inc.

Infusion versus bolus of an ultrasound contrast agent: in vivo dose-response measurements of BR1

RATIONALE AND OBJECTIVES

To determine the efficacy of an ultrasound contrast agent infusion using Doppler intensitometry estimation of backscatter enhancement in blood.

METHODS

Multiple intravenous injections of BR1 (SonoVue) were performed in chronic dog studies, using bolus (0.05-2 mL) and infusion (3-40 mL/h during 6 minutes) administration. The pulsed Doppler signal from the femoral artery was recorded and analyzed for mean Doppler power and integrated fractional enhancement.

RESULTS

For bolus injection, time-intensity curves exhibited a rapid first pass (peak 30 dB for 0.45 mL) followed by a slower washout. Integrated fractional enhancement exhibited a linear relation with the dose (R2 = 0.99). For infusion administration, peak enhancement increased with the infusion rate from 8 to 22 dB. At rates exceeding 30 mL/h, the enhancement was stable with a plateau-like pattern.

CONCLUSIONS

Infusion of BR1 is easily achieved and allows the duration of enhancement to be increased as long as desired. Stable enhancement is obtained for rates greater than 30 mL/h.

The Growth of Silver on an Ordered Alumina Surface

The growth of Ag on an ordered Al2O3 surface was studied by low energy ion scattering spectroscopy (LEIS), scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and temperature programmed desorption (TPD). Three-dimensional (3D) growth of Ag clusters was observed with STM and LEIS, with the cluster size increasing with Ag coverage. The XPS core level binding energies and the Auger parameters indicate a weak interaction between the Ag clusters and the Al2O3 support. Final state effects are determined to be the primary contribution to the Ag core level binding energy shift. Nonzero order kinetics was observed for Ag desorption in TPD with the Ag sublimation energy decreasing with decreasing cluster size.

The TCR repertoire of an immunodominant CD8+ T lymphocyte population

The TCR repertoire of an epitope-specific CD8(+) T cell population remains poorly characterized. To determine the breadth of the TCR repertoire of a CD8(+) T cell population that recognizes a dominant epitope of the AIDS virus, the CD8(+) T cells recognizing the tetrameric Mamu-A*01/p11C(,CM) complex were isolated from simian immunodeficiency virus (SIV)-infected Mamu-A*01(+) rhesus monkeys. This CD8(+) T cell population exhibited selected usage of TCR V beta families and complementarity-determining region 3 (CDR3) segments. Although the epitope-specific CD8(+) T cell response was clearly polyclonal, a dominance of selected V beta(+) cell subpopulations and clones was seen in the TCR repertoire. Interestingly, some of the selected V beta(+) cell subpopulations and clones maintained their dominance in the TCR repertoire over time after infection with SIV of macaques. Other V beta(+) cell subpopulations declined over time in their relative representation and were replaced by newly evolving clones that became dominant. The present study provides molecular evidence indicating that the TCR repertoire shaped by a single viral epitope is dominated at any point in time by selected V beta(+) cell subpopulations and clones and suggests that dominant V beta(+) cell subpopulations and clones can either be stable or evolve during a chronic infection.

Characterization and transplantation of enteric neural crest cells from human induced pluripotent stem cells

The enteric nervous system (ENS) is recognized as a second brain because of its complexity and its largely autonomic control of bowel function. Recent progress in studying the interactions between the ENS and the central nervous system (CNS) has implicated alterations of the gut/brain axis as a possible mechanism in the pathophysiology of autism spectrum disorders (ASDs), Parkinson's disease (PD) and other human CNS disorders, whereas the underlying mechanisms are largely unknown because of the lack of good model systems. Human induced pluripotent stem cells (hiPSCs) have the ability to proliferate indefinitely and differentiate into cells of all three germ layers, thus making iPSCs an ideal source of cells for disease modelling and cell therapy. Here, hiPSCs were induced to differentiate into neural crest stem cells (NCSCs) efficiently. When co-cultured with smooth muscle layers of ganglionic gut tissue, the NCSCs differentiated into different subtypes of mature enteric-like neurons expressing nitric oxide synthase (nNOS), vasoactive intestinal polypeptide (VIP), choline acetyltransferase (ChAT) or calretinin with typical electrophysiological characteristics of functional neurons. Furthermore, when they were transplanted into aneural or aganglionic chick, mouse or human gut tissues in ovo, in vitro or in vivo, hiPSC-derived NCSCs showed extensive migration and neural differentiation capacity, generating neurons and glial cells that expressed phenotypic markers characteristic of the enteric nervous system. Our results indicate that enteric NCSCs derived from hiPSCs supply a powerful tool for studying the pathogenesis of gastrointestinal disorders and brain/gut dysfunction and represent a potentially ideal cell source for enteric neural transplantation treatments.

Cloning and sequencing of a cellobiose phosphotransferase system operon from Bacillus stearothermophilus XL-65-6 and functional expression in Escherichia coli

Cellulolytic strains of Bacillus stearothermophilus were isolated from nature and screened for the presence of activities associated with the degradation of plant cell walls. One isolate (strain XL-65-6) which exhibited strong activities with 4-methylumbelliferyl-beta-D-glucopyranoside (MUG) and 4-methylumbelliferyl-beta-D-cellobiopyranoside (MUC) was used to construct a gene library in Escherichia coli. Clones degrading these model substrates were found to encode the cellobiose-specific genes of the phosphoenolpyruvate-dependent phosphotransferase system (PTS). Both MUG and MUC activities were present together, and both activities were lost concurrently during subcloning experiments. A functional E. coli ptsI gene was required for MUC and MUG activities (presumably a ptsH gene also). The DNA fragment from B. stearothermophilus contained four open reading frames which appear to form a cel operon. Intergenic stop codons for celA, celB, and celC overlapped the ribosomal binding sites of the respective downstream genes. Frameshift mutations or deletions in celA, celB, and celD were individually shown to result in a loss of MUC and MUG activities. On the basis of amino acid sequence homology and hydropathy plots of translated sequences, celA and celB were identified as encoding PTS enzyme II and celD was identified as encoding PTS enzyme III. These translated sequences were remarkably similar to their respective E. coli homologs for cellobiose transport. No reported sequences exhibited a high level of homology with the celC gene product. The predicted carboxy-terminal region for celC was similar to the corresponding region of E. coli celF, a phospho-beta-glucosidase. An incomplete regulatory gene (celR) and proposed promoter sequence were located 5' to the proposed cel operon. A stem-loop resembling a rho-independent terminator was present immediately downstream from celD. These results indicate that B. stearothermophilus XL-65-6 contains a cellobiose-specific PTS for cellobiose uptake. Similar systems may be present in other gram-positive bacteria.

Isolation and molecular characterization of high-performance cellobiose-fermenting spontaneous mutants of ethanologenic Escherichia coli KO11 containing the Klebsiella oxytoca casAB operon

Escherichia coli KO11 was previously constructed to produce ethanol from acid hydrolysates of hemicellulose (pentoses and hexoses) by the chromosomal integration of Zymomonas mobilis genes encoding pyruvate decarboxylase (pdc) and alcohol dehydrogenase (adhB). Klebsiella oxytoca P2 was constructed in an analogous fashion for the simultaneous saccharification and fermentation of cellulose and contains PTS enzymes for cellobiose. In this study, KO11 was further engineered for the fermentation of cellulose by adding the K. oxytoca casAB genes encoding Enzyme IIcellobiose and phospho-beta-glucosidase. Although the two K. oxytoca genes were well expressed in cloning hosts such as DH5 alpha, both were expressed poorly in E. coli KO11, a derivative of E. coli B. Spontaneous mutants which exhibited more than 15-fold-higher specific activities for cellobiose metabolism were isolated. The mutations of these mutants resided in the plasmid rather than the host. Three mutants were characterized by sequence analysis. All contained similar internal deletions which eliminated the casAB promoter and operator regions and placed the lacZ Shine-Dalgarno region immediately upstream from the casA Shine-Dalgarno region. KO11 harboring mutant plasmids (pLOI1908, pLOI1909, or pLOI1910) rapidly fermented cellobiose to ethanol, and the yield was more than 90% of the theoretical yield. Two of these strains were used with commercial cellulase to ferment mixed-waste office paper to ethanol.

Cloning of cellobiose phosphoenolpyruvate-dependent phosphotransferase genes: functional expression in recombinant Escherichia coli and identification of a putative binding region for disaccharides

Genomic libraries from nine cellobiose-metabolizing bacteria were screened for cellobiose utilization. Positive clones were recovered from six libraries, all of which encode phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS) proteins. Clones from Bacillus subtilis, Butyrivibrio fibrisolvens, and Klebsiella oxytoca allowed the growth of recombinant Escherichia coli in cellobiose-M9 minimal medium. The K. oxytoca clone, pLOI1906, exhibited an unusually broad substrate range (cellobiose, arbutin, salicin, and methylumbelliferyl derivatives of glucose, cellobiose, mannose, and xylose) and was sequenced. The insert in this plasmid encoded the carboxy-terminal region of a putative regulatory protein, cellobiose permease (single polypeptide), and phospho-beta-glucosidase, which appear to form an operon (casRAB). Subclones allowed both casA and casB to be expressed independently, as evidenced by in vitro complementation. An analysis of the translated sequences from the EIIC domains of cellobiose, aryl-beta-glucoside, and other disaccharide permeases allowed the identification of a 50-amino-acid conserved region. A disaccharide consensus sequence is proposed for the most conserved segment (13 amino acids), which may represent part of the EIIC active site for binding and phosphorylation.

Towards an understanding of the nucleation of alpha-para amino benzoic acid from ethanolic solutions: a multi-scale approach

The molecular assembly and subsequent nucleation of para-amino benzoic acid (PABA) from ethanolic solutions is probed using a multi-scale and multi-technique approach. This is applied by examining and interrelating information regarding the molecular, solution-state, cluster, solid-state and surface structures to understand why the alpha form of PABA is crystallised in preference to its low temperature beta form. Calculations suggest that conformational changes within the solute molecule play little or no role in directing the nucleation of either the alpha or beta crystal forms. Combined ab initio and molecular dynamics calculations of the stability of small clusters in solution suggests that the hydrogen-bonded carboxylic acid dimers, present in the alpha structure, are the most stable in solution and play a major role in the self-assembly and polymorphic expression of the alpha form in ethanol in preference to the beta form. These calculations are in good agreement with X-ray small-angle scattering analysis which reveals the presence of PABA clusters in ethanol which are consistent with the size and shape of a carboxylic acid dimer. SAXS studies also reveal the presence of larger cluster structures in a size range 10-40 nm which appear to grow, perhaps reflecting a change in the balance between monomers and dimers within the solution during the nucleation process. The results of crystallisation-kinetics experiments indicate an instantaneous nucleation mechanism where the number of instantaneously nucleated crystallites is calculated to be 1360-660 nuclei per ml and the subsequent growth is found to be only rate limited by diffusion of the growth unit to the crystallite surface. A linear dependence of growth rate with respect to supersaturation is observed for the (0 1 -1) capping face, which is associated with strong π-π stacking interactions. This is consistent with a solid-on-solid mechanism associated with surface roughened growth and concomitant poor lattice-perfection. Conversely, the side (1 0 -1) surface has a growth mechanism consistent with a 2D nucleation birth and spread mechanism. Hence, these mechanisms result in very fast growth along the b-axis and the needle-like morphology that is observed for alpha-PABA.

Immune biology of macaque lymphocyte populations during mycobacterial infection

Immune responses of lymphocyte populations during early phases of mycobacterial infection and reinfection have not been well characterized in humans. A non-human primate model of Mycobacterium bovis bacille Calmette-Guerin (BCG) infection was employed to characterize optimally the immune responses of mycobacteria-specific T cells. Primary BCG infection induced biphasic immune responses, characterized by initial lymphocytopenia and subsequent expansion of CD4+, CD8+ and gammadelta T cell populations in the blood, lymph nodes and the pulmonary compartment. The potency of detectable T cell immune responses appears to be influenced by the timing and route of infection as well as challenge doses of BCG organisms. Systemic BCG infection introduced by intravenous challenge induced a dose-dependent expansion of circulating CD4+, CD8+ and gammadelta T cells whereas, in the pulmonary compartment, the systemic infection resulted in a predominant increase in numbers of gammadelta T cells. In contrast, pulmonary exposure to BCG through the bronchial route induced detectable expansions of CD4+, CD8+ and gammadelta T cell populations in only the lung but not in the blood. A rapid recall expansion of these T cell populations was seen in the macaques reinfected intravenously and bronchially with BCG. The expanded alphabeta and gammadelta T cell populations exhibited their antigen specificity for mycobacterial peptides and non-peptide phospholigands, respectively. Finally, the major expansion of T cells was associated with a resolution of active BCG infection and reinfection. The patterns and kinetics of CD4+, CD8+ and gammadelta T cell immune responses during BCG infection might contribute to characterizing immune protection against tuberculosis and testing new tuberculosis vaccines in primates.

Differential expression profile of hepatic circular RNAs in chronic hepatitis B

CircRNAs exert gene regulatory effects by sequestering target microRNAs (miRNAs) and play a vital role in the onset and development of disease. Until recently, little has been known about the expression, regulation and biological function of circRNAs in both health and chronic hepatitis B (CHB).To identify hepatic circRNAs associated with CHB, we performed RNA sequencing using liver biopsies from untreated CHB patients and controls. We then established a bioinformatics pipeline for identification of CHB-associated circRNAs and in silico analysis of the circRNA-miRNA-mRNA pathways. We used quantitative reverse transcription polymerase chain reaction (qRT-PCR) to confirm these results. The profiles of hepatic circRNA expression were significantly different in CHB compared with controls, with a total of 99 dysregulated circRNAs identified to be correlated with CHB. Computational analysis of the circRNA-miRNA-mRNA pathways revealed a large number of miRNAs (665), which were putatively targeted by the differentially expressed hepatic circRNAs. Interestingly, four of the predicted CHB-related circRNA-miRNA-mRNA pathways were found to be involved in the pathogenesis of HBV infection and progression of HBV-associated liver disease. Among these pathways, regression analysis of gene expression revealed a strong positive correlation between hsa_circ_0000650 and TGFβ2 and a negative correlation between hsa_circ_0000650 and miR-6873-3p, which hinted that hsa_circ_0000650 interacted with TGFβ2 mediated by miR-6873-3p. This study firstly demonstrates that patients with CHB present different profiles of hepatic circRNAs and circRNA/miRNA interactions. Thus, circRNAs have promise as novel mechanisms underlying the pathogenesis and progression of CHB.

The influence of solution environment on the nucleation kinetics and crystallisability of para-aminobenzoic acid

The influence of solvent on the solution thermodynamics, nucleation-kinetics and crystal growth of alpha para-aminobenzoic acid (PABA) crystallising from supersaturated solutions, is examined through analysis of the metastable zone width.

Tim-3 exacerbates kidney ischaemia/reperfusion injury through the TLR-4/NF-κB signalling pathway and an NLR-C4 inflammasome activation

T cell immunoglobulin domain and mucin domain-containing molecule-3 (Tim-3), a member of the immunoglobulin superfamily, has been shown to play a crucial role in host adaptive immunity and tolerance. However, its role in kidney ischaemia-reperfusion injury (IRI) remains unknown. In this study, we investigated the role and mechanism of Tim-3 signalling after kidney IRI. In an established murine model of kidney IRI, we found that Tim-3 expression is enhanced on monocytes/macrophages. Anti-Tim-3 antibody RMT3-23 ameliorates biochemical and histological kidney injury, reduces apoptosis and decreases macrophage infiltration and cytokine production in ischaemic kidneys. Cell culture experiments also demonstrated that the role of Tim-3 in IRI-induced macrophage activation leads to the secretion of proinflammatory cytokines and chemokines. In addition, Toll-like receptor (TLR)-4 and Nod-like receptor (NLR) family CARD domain-containing protein 4 (NLR-C4) expression were enhanced after kidney IRI and decreased significantly by RMT3-23. Tim-3 not only promotes TLR-mediated nuclear factor kappa B (NF-κB) activation and cytokine and chemokine release, but also participates in NLR-C4 inflammasome activation. Taken together, our data confirm that Tim-3 signalling enhances injury after kidney IRI and demonstrated that Tim-3 is involved in regulating TLR-4/NF-κB signalling and NLR-C4 inflammasome activation, which provide evidence that Tim-3 signalling is critical for kidney IRI and may provide a new means to ameliorate kidney tissue immune responses in the clinics.

Indoor allergen levels in Guangzhou city, southern China

BACKGROUND

  High levels of sensitization to house dust mites have been observed in Chinese allergic patients. This study has measured levels and distributions of mite and cockroach allergens in household dust in Guangzhou. Influences of home characteristics and seasonal changes on allergen levels were also investigated.

METHODS

  Dust samples were collected from bedding and living room from households in Guangzhou. Major allergens from Dermatophagoides pteronyssinus, D. farinae, D. microceras, Blomia tropicalis and cockroach allergens were measured by ELISA. Home characteristics were obtained from a questionnaire.

RESULTS

  Four hundred and four dust samples were collected from 107 homes during October 2006 to November 2007. House dust mite allergen levels were detectable in 99% of the bedding samples. Der f 1 levels were significantly higher than Der p 1 levels. High levels of mite allergens (>10 μg/g) were observed in 88% of all the bedding samples. Cockroach allergens were detected in 93% of households and were higher in living room samples than in bedding samples. Blo t 5 and Der m 1 could not be detected in the dust samples. Having fabric furniture was a predictor of high allergen levels. Der f 1 levels were higher in summer time than in winter time. Cockroach allergens were higher in winter time than in summer time.

CONCLUSION

  In Guangzhou, Der f 1 is the predominant mite allergen in dust with very high levels in bedding. Cockroach allergens are also common.

Interpolation methods for time-delay estimation using cross-correlation method for blood velocity measurement

The cross-correlation method (CCM) for blood flow velocity measurement using Doppler ultrasound is based on time delay estimation of echoes from pulse-to-pulse. The sampling frequency of the received signal is usually kept as low as possible in order to reduce computational complexity, and the peak in the correlation function is found by interpolating the correlation function. The parabolic-fit interpolation method introduces a bias at low sampling rate to the ultrasound center frequency ratio. In this study, four different methods are suggested to improve the estimation accuracy: (1) Parabolic interpolation with bias-compensation, derived from a theoretical signal model. (2) Parabolic interpolation combined with linear filter interpolation of the correlation function. (3) Parabolic interpolation to the complex correlation function envelope. (4) Matched filter interpolation applied to the correlation function. The new interpolation methods are analyzed both by computer simulated signals and RF-signals recorded from a patient with time delay larger than 1/f(0), where f(0) is the center frequency. The simulation results show that these methods are more accurate than the parabolic-fit method. From the simulation, the worst estimation accuracy is about 1.25% of 1/f(0) for the parabolic-fit interpolation, and it is improved by the above methods to less than 0.5% of 1/f(0) when the sampling rate is 10 MHz, the center frequency is 2.5 MHz and the bandwidth is 1 MHz. This improvement also can be observed in the experimental data. Furthermore, the matched filter interpolation gives the best performance when signal-to-noise ratio (SNR) is low. This is verified both by simulation and experimentation.