Consequences of bile salt biotransformations by intestinal bacteria

Emerging evidence strongly suggest that the human "microbiome" plays an important role in both health and disease. Bile acids function both as detergents molecules promoting nutrient absorption in the intestines and as hormones regulating nutrient metabolism. Bile acids regulate metabolism via activation of specific nuclear receptors (NR) and G-protein coupled receptors (GPCRs). The circulating bile acid pool composition consists of primary bile acids produced from cholesterol in the liver, and secondary bile acids formed by specific gut bacteria. The various biotransformation of bile acids carried out by gut bacteria appear to regulate the structure of the gut microbiome and host physiology. Increased levels of secondary bile acids are associated with specific diseases of the GI system. Elucidating methods to control the gut microbiome and bile acid pool composition in humans may lead to a reduction in some of the major diseases of the liver, gall bladder and colon.

Gut microbiota, cirrhosis, and alcohol regulate bile acid metabolism in the gut

The understanding of the complex role of the bile acid-gut microbiome axis in health and disease processes is evolving rapidly. Our focus revolves around the interaction of the gut microbiota with liver diseases, especially cirrhosis. The bile acid pool size has recently been shown to be a function of microbial metabolism of bile acid, and regulation of the microbiota by bile acids is important in the development and progression of several liver diseases. Humans produce a large, conjugated hydrophilic bile acid pool, maintained through positive-feedback antagonism of farnesoid X receptor (FXR) in the intestine and liver. Microbes use bile acids, and via FXR signaling this results in a smaller, unconjugated hydrophobic bile acid pool. This equilibrium is critical to maintain health. The challenge is to examine the manifold functions of gut bile acids as modulators of antibiotic, probiotic, and disease progression in cirrhosis, metabolic syndrome, and alcohol use. Recent studies have shown potential mechanisms explaining how perturbations in the microbiome affect bile acid pool size and composition. With advancing liver disease and cirrhosis, there is dysbiosis in the fecal, ileal, and colonic mucosa, in addition to a decrease in bile acid concentration in the intestine due to the liver problems. This results in a dramatic shift toward the Firmicutes, particularly Clostridium cluster XIVa, and increasing production of deoxycholic acid. Alcohol intake speeds up these processes in the subjects with and without cirrhosis without significant FXR feedback. Taken together, these pathways can impact intestinal and systemic inflammation while worsening dysbiosis. The interaction between bile acids, alcohol, cirrhosis, and dysbiosis is an important relationship that influences intestinal and systemic inflammation, which in turn determines progression of the overall disease process. These interactions and the impact of commonly used therapies for liver disease can provide insight into the pathogenesis of inflammation in humans.

Synthesis and properties of nanohybrid materials with SiO2 and epoxy resin

SiO2-epoxy nanohybrid materials were synthesized by hybridization of surface-modified colloidal silica nanoparticle (CS) and epoxy resin. The CS was surface-modified with either methyltrimethoxysilane (MTMS) or phenyltrimethoxysilane (PTMS) followed by the solvent exchange with dimethylacetamide (DMAc) to have a homogenous dispersion in epoxy resin. Various amounts of surface-modified CS were mixed with epoxy resin. The chemical structures of surface-modified CS were investigated with FT-IR spectroscopy. The particle sizes of CS and surface-modified CS were measured with DLS. The morphology of hybrid materials analyzed using FE-SEM and AFM showed homogeneous dispersion in epoxy resin. The optical and thermal properties of the hybrid materials determined by refractive index meter and DSC were lower in RI and higher in Tg than neat epoxy resin, respectively.

Effect of SiO2-acryl nanohybrid coating layers on transparent conducting oxide-poly(ethylene terephthalate) superstrate

SiO2-acryl nanohybrid coating layers were produced by hybridizing acrylic resin and surface-modified colloidal silica (CS) nanoparticles. First, CS nanoparticles were modified with methyltrimethoxysilane (MTMS) and vinyltrimethoxysilane (VTMS) by a sol-gel process. The surface-modified CS nanoparticles were then solvent-exchanged to be homogeneous in acrylic resin. The Hybrid materials were mixed in variation with the amount of surface-modified CS nanoparticles, coated with poly(ethylene terephthalate) (PET), then finally cured by UV light to obtain a hybrid coating layer. Field emission scanning electron microscopy (FE-SEM), particle size analysis (using a Zetasizer), and atomic force microscopy (AFM) were performed to determine the morphology of the hybrid thin-films. Thermogravimetric analysis (TGA) was used to investigate the thermal properties. Fourier-transform infrared (FTIR), ultraviolet-visible (UVNis) spectroscopies, and pencil hardness were used to obtain the details of chemical structures, optical properties, and hardness, respectively. The hybrid thin films had shown to be enhanced properties compared to their urethane acrylate prepolymer (UAP) coating film.

A disintegrin and metalloproteinase 10 regulates antibody production and maintenance of lymphoid architecture

A disintegrin and metalloproteinase 10 (ADAM10) is a zinc-dependent proteinase related to matrix metalloproteinases. ADAM10 has emerged as a key regulator of cellular processes by cleaving and shedding extracellular domains of multiple transmembrane receptors and ligands. We have developed B cell-specific ADAM10-deficient mice (ADAM10(B-/-)). In this study, we show that ADAM10 levels are significantly enhanced on germinal center B cells. Moreover, ADAM10(B-/-) mice had severely diminished primary and secondary responses after T-dependent immunization. ADAM10(B-/-) displayed impaired germinal center formation, had fewer follicular Th cells, decreased follicular dendritic cell networks, and altered chemokine expression in draining lymph nodes (LNs). Interestingly, when spleen and LN structures from immunized mice were analyzed for B and T cell localization, tissues structure was aberrant in ADAM10(B-/-) mice. Importantly, when ADAM10-deficient B cells were stimulated in vitro, they produced comparable Ab as wild type B cells. This result demonstrates that the defects in humoral responses in vivo result from inadequate B cell activation, likely because of the decrease in follicular Th cells and the changes in structure. Thus, ADAM10 is essential for the maintenance of lymphoid structure after Ag challenge.

ADAM10 overexpression shifts lympho- and myelopoiesis by dysregulating site 2/site 3 cleavage products of Notch

Although the physiological consequences of Notch signaling in hematopoiesis have been extensively studied, the differential effects of individual notch cleavage products remain to be elucidated. Given that ADAM10 is a critical regulator of Notch and that its deletion is embryonically lethal, we generated mice that overexpress ADAM10 (ADAM10 transgenic [A10Tg]) at early stages of lympho- and myeloid development. Transgene expression resulted in abrogated B cell development, delayed T cell development in the thymus, and unexpected systemic expansion of CD11b(+)Gr-1(+) cells, also known as myeloid-derived suppressor cells. Mixed bone marrow reconstitution assays demonstrated that transgene expression altered hematopoiesis via a cell-intrinsic mechanism. Consistent with previously reported observations, we hypothesized that ADAM10 overexpression dysregulated Notch by uncoupling the highly regulated proteolysis of Notch receptors. This was confirmed using an in vitro model of hematopoiesis via culturing A10Tg hematopoietic Lineage(-)Sca-1(+)c-Kit(+) cells with OP-9 stromal cells in the presence or absence of Delta-like 1, a primary ligand for Notch. Blockade of the site 2 (S2) and site 3 (S3) cleavage of the Notch receptor demonstrated differential effects on hematopoiesis. OP9-DL1 cultures containing the ADAM10 inhibitor (S2 cleavage site) enhanced and rescued B cell development from wild-type and A10Tg Lineage(-)Sca-1(+)c-Kit(+) cells, respectively. In contrast, blockade of γ-secretase at the S3 cleavage site induced accumulation of the S2 product and consequently prevented B cell development and resulted in myeloid cell accumulation. Collectively, these findings indicate that the differential cleavage of Notch into S2 and S3 products regulated by ADAM10 is critical to hematopoietic cell-fate determination.

Isolation and characterization of a bile acid inducible 7alpha-dehydroxylating operon in Clostridium hylemonae TN271

Primary bile acids are synthesized from cholesterol in the liver, conjugated to either glycine or taurine and secreted into bile. Bile salts undergo enterohepatic circulation several times each day. During this process, they are biotransformed into a variety of metabolites by gut bacteria. The major biotransformation is the 7alpha-dehydroxylation of cholic acid and chenodeoxycholic acid yielding deoxycholic acid and lithocholic acid, respectively. 7alpha-Dehydroxylation is a multi-step pathway. The genes encoding enzymes in this pathway have been identified in two species of "high" activity strains of clostridia. Here, we report the isolation and characterization of a bile acid inducible (bai) operon in Clostridium hylemonae, a "low" activity 7alpha-dehydroxylating strain. The gene organization and sequence of the baiBCDEFGHI operon was highly conserved between C. hylemonae and "high" activity strains. Surprisingly, the baiA gene was missing from the bai operon of C. hylemonae. The baiA gene was isolated using PCR and degenerate oligonucleotide primers. The mRNA start site for the large bai operon was determined and shown to be only 11bp from the initiation codon of the first gene. It was also discovered that allocholic acid (5alpha) induced the bai operon and stimulated the conversion of [24-(14)C] cholic acid to [24-(14)C] allodeoxycholic acid in cultures of C. scindens and C. hylemonae allodeoxycholic acid. Finally, it was discovered that the addition of testosterone to the growth medium markedly increased 7alpha-dehydroxylation of cholic acid in Clostridium scindens and C. hylemonae. We hypothesize that testosterone may be a gratuitous inducer of genes involved in the reductive arm of the bile acid 7alpha-dehydroxylation pathway.

High dielectric loss in graphite-coated Ti nanocapsules

Graphite-coated Ti nanocapsules, with Ti nanoparticles as core and onion-like graphite layers as shell, have been prepared by a modified arc-discharge method in ethanol atmosphere, and characterized by means of X-ray diffraction, transmission electron microscopy and Raman spectroscopy. The dielectric properties of the graphite-coated Ti nanocapsules have been investigated in the 2-18 GHz range. An equivalent circuit model was used to interpret the non-linear dielectric resonance behavior of the graphite-coated Ti nanocapsules. The high dielectric loss is mainly attributed to conductance loss and dipole-relaxation loss in the graphite-coated Ti nanocapsules. The graphite-coated Ti nanocapsules exhibit promising properties for application as a new type of shield or absorbent of electromagnetic waves.

ADAM10 is essential for Notch2-dependent marginal zone B cell development and CD23 cleavage in vivo

The proteolytic activity of a disintegrin and metalloproteinase 10 (ADAM10) regulates cell-fate decisions in Drosophila and mouse embryos. However, in utero lethality of ADAM10^−/− mice has prevented examination of ADAM10 cleavage events in lymphocytes. To investigate their role in B cell development, we generated B cell–specific ADAM10 knockout mice. Intriguingly, deletion of ADAM10 prevented development of the entire marginal zone B cell (MZB) lineage. Additionally, cleavage of the low affinity IgE receptor, CD23, was profoundly impaired, but subsequent experiments demonstrated that ADAM10 regulates CD23 cleavage and MZB development by independent mechanisms. Development of MZBs is dependent on Notch2 signaling, which requires proteolysis of the Notch2 receptor by a previously unidentified proteinase. Further experiments revealed that Notch2 signaling is severely impaired in ADAM10-null B cells. Thus, ADAM10 critically regulates MZB development by initiating Notch2 signaling. This study identifies ADAM10 as the in vivo CD23 sheddase and an important regulator of B cell development. Moreover, it has important implications for the treatment of numerous CD23- and Notch-mediated pathologies, ranging from allergy to cancer.

ADAM10 regulates B cell development and immunoglobulin production (138.6)

Members of the disintegrin and metalloprotease (ADAM) family can regulate lymphocyte development and function by cleaving membrane receptors. Previous studies showed that ADAM10 cleaves the B cell receptors, CD23 and Notch2, in vitro. However, in the absence of in vivo models, the physiologic impact of these events has not been examined. Thus, we generated B cell-specific ADAM10 KO and transgenic (Tg) mice to determine the role of ADAM10 in B cell development and function. Notch signaling regulates the differentiation of common lymphoid progenitors (CLPs) by promoting T cell fate. Accordingly, overexpression of ADAM10 in CLPs completely blocked B cell development. Deletion of ADAM10 from B cells in ADAM10fl/fl, CD19-cre+ mice prevented differentiation of marginal zone B cells, which is dependent on Notch2 signaling. In addition, expression of CD23 on ADAM10null B cells was dramatically elevated while levels of soluble CD23 were reduced in serum. As a result, IgE production by ADAM10fl/fl, CD19-cre+ mice was remarkably suppressed upon immunization, mimicking the response of CD23Tg mice. Finally, production of IgG1 and IgG2b was profoundly inhibited, suggesting a novel role for ADAM10 in class-switching to IgG. These results illustrate the physiologic role of ADAM10 in Notch signaling and CD23 cleavage. Moreover, they identify ADAM10 as a critical regulator of B cell development and immunoglobulin production.

AHA 0815066E, NIAID R01AI18697, NIAID U19AI077435

Controlled growth of vertically aligned ZnO nanowires with different crystal orientation of the ZnO seed layer

A novel synthesis and growth method achieving vertically aligned zinc oxide (ZnO) nanowires on a silicon dioxide (SiO(2)) coated silicon (Si) substrate is demonstrated. The growth direction of the ZnO nanowires is determined by the crystal structure of the ZnO seed layer, which is formed by the oxidation of a DC-sputtered Zn film. The [002] crystal direction of the seed layer is dominant under optimized thickness of the Zn film and thermal treatment. Vertically aligned ZnO nanowires on SiO(2) coated Si substrate are realized from the appropriately thick oxidized Zn seed layer by a vapor-solid growth mechanism by catalyst-free thermal chemical vapor deposition (CVD). These experimental results raise the possibility of using the nanowires as functional blocks for high-density integration systems and/or photonic applications.

Clostridium scindens baiCD and baiH genes encode stereo-specific 7alpha/7beta-hydroxy-3-oxo-delta4-cholenoic acid oxidoreductases

Secondary bile acids, formed by intestinal bacteria, are suggested to play a significant role in cancers of the gastrointestinal tract in humans. Bile acid 7alpha/beta-dehydroxylation is carried out by a few species of intestinal clostridia which harbor a multi-gene bile acid inducible (bai) operon. Several genes encoding enzymes in this pathway have been cloned and characterized. However, no gene product(s) has yet been assigned to the production of 3-oxo-Delta4-cholenoic acid intermediates of cholic acid (CA), chenodeoxycholic acid (CDCA) or ursodeoxycholic acid (UDCA). We previously reported that the baiH gene encodes an NADH:flavin oxidoreductase (NADH:FOR); however, the role of this protein in bile acid 7-dehydroxylation is unclear. Homology searches and secondary structural alignments suggest this protein to be similar to flavoproteins which reduce alpha/beta-unsaturated carbonyl compounds. The baiH gene product was expressed in Escherichia coli, purified and discovered to be a stereo-specific NAD(H)-dependent 7beta-hydroxy-3-oxo-Delta4-cholenoic acid oxidoreductase. Additionally, high sequence similarity between the baiH and baiCD gene products suggests the baiCD gene may encode a 3-oxo-Delta4-cholenoic acid oxidoreductase specific for CDCA and CA. We tested this hypothesis using cell extracts prepared from E. coli overexpressing the baiCD gene and discovered that it encodes a stereo-specific NAD(H)-dependent 7alpha-hydroxy-3-oxo-Delta4-cholenoic acid oxidoreductase.

Bile salt biotransformations by human intestinal bacteria

Secondary bile acids, produced solely by intestinal bacteria, can accumulate to high levels in the enterohepatic circulation of some individuals and may contribute to the pathogenesis of colon cancer, gallstones, and other gastrointestinal (GI) diseases. Bile salt hydrolysis and hydroxy group dehydrogenation reactions are carried out by a broad spectrum of intestinal anaerobic bacteria, whereas bile acid 7-dehydroxylation appears restricted to a limited number of intestinal anaerobes representing a small fraction of the total colonic flora. Microbial enzymes modifying bile salts differ between species with respect to pH optima, enzyme kinetics, substrate specificity, cellular location, and possibly physiological function. Crystallization, site-directed mutagenesis, and comparisons of protein secondary structure have provided insight into the mechanisms of several bile acid-biotransforming enzymatic reactions. Molecular cloning of genes encoding bile salt-modifying enzymes has facilitated the understanding of the genetic organization of these pathways and is a means of developing probes for the detection of bile salt-modifying bacteria. The potential exists for altering the bile acid pool by targeting key enzymes in the 7alpha/beta-dehydroxylation pathway through the development of pharmaceuticals or sequestering bile acids biologically in probiotic bacteria, which may result in their effective removal from the host after excretion.

Fluorescence scanning near-field optical microscopy of polyfluorene composites

Fluorescence scanning near-field optical microscopy (SNOM) is used to investigate binary polyfluorene-based composites of varying composition. The samples investigated contain blends of the polymer poly(9,9'-dioctylfluorene-cobenzothiadiazole), F8BT, with similar polyfluorenes of wider band gap. Images acquired from a film containing 50% by weight F8BT exhibit a high degree of correlation between the topography and fluorescence, with an F8BT-rich phase which protrudes from the surface of the film forming isolated regions with sizes from hundreds of nanometres to several micrometres. A film containing 10% by weight F8BT also has micrometre-size F8BT-rich regions, but also present are small and locally varying proportions of F8BT in the other polyfluorene component phase, indicating a hierarchy of phases within this sample. The fluorescence and topographic images of a third sample studied, containing 90% by weight F8BT, display no correlation, demonstrating that it is not always appropriate to use topographic information to determine the phase structure within polymer blends. The fluorescence SNOM images acquired from these samples are able to assist our understanding of the photovoltaic efficiency of devices fabricated from these films, which are governed by the extent of the interfacial area between these two constituent polymers.