C.W. Won

Macrolide Treatment for Mycobacterium abscessus and Mycobacterium massiliense Infection and Inducible Resistance

RATIONALE Macrolides, such as clarithromycin (CLR) and azithromycin (AZM), are frequently the only oral antibiotics that are active against Mycobacterium abscessus and M. massiliense infections. OBJECTIVES To compare the activity of CLR and AZM in experimental models. METHODS We compared the treatment efficacies of CLR and AZM and determined the correlation between efficacy and induced erythromycin ribosome methyltransferase gene (erm)(41) expression in experimental models of M. abscessus and M. massiliense infections. MEASUREMENTS AND MAIN RESULTS In all tested M. abscessus isolates, a high level of inducible CLR resistance developed (minimal inhibitory concentration [MIC] on Day 3 versus Day 14; P < 0.001). Whereas the AZM MIC increased on Day 14 (P < 0.01 versus Day 3), the level was significantly lower than the CLR MIC on Day 14 (P < 0.001). However, the MICs of CLR and AZM for the M. massiliense isolates did not change. Compared with CLR, AZM presented greater antibiotic activity against M. abscessus in vitro, ex vivo, and in vivo (P < 0.05), whereas both macrolides were comparably effective against M. massiliense. In M. abscessus infection, the level of erm(41) expression was higher after exposure to CLR than after exposure to AZM (P < 0.001). Experiments using an erm(41)-knockout M. abscessus mutant and an M. massiliense transformant expressing M. abscessus erm(41) confirmed that erm(41) was responsible for inducible CLR resistance. CONCLUSIONS CLR induces greater erm(41) expression and thus higher macrolide resistance than AZM in M. abscessus infection. AZM may be more effective against M. abscessus, whereas both macrolides appear to be equally effective against M. massiliense.

The effects of processing parameters on the microstructure and mechanical properties of modified B390 alloy in direct squeeze casting

Abstract The direct squeeze casting of B390 has been investigated as a function of melt temperature and applied pressure. Commercial finite volume method (FVM) computer code for heat transfer analysis, MAGMAsoft, was used to simulate cooling curves obtained from the direct squeeze casting process. The experimental and modeling results are discussed, and the correlation between cooling rate and microstructure is studied. The effects of applied pressures and melt temperature on the formation of primary Si and Chinese scripts are also discussed in connection with mechanical properties such as hardness and tensile strength.

Effect of the gap distance on the cooling behavior and the microstructure of indirect squeeze cast and gravity die cast 5083 wrought Al alloy

Abstract An indirect squeeze casting process applied to a wrought 5083 Al alloy (Al–4.7Mg–0.7Mn) was investigated experimentally and numerically. A two-dimensional finite element computer code for fully coupled heat transfer and deformation analysis, abaqus , was used to simulate the cooling curves obtained from the experiments. Thermal contraction of the material during solidification creates an air gap between the mold and the cooling material. The formation of this air gap is explained using the calculated results. The experimental and predicted results are discussed in conjunction with the relationships between the cooling rate, microstructure, die geometry and applied pressure. The effect of applied pressure and cooling rate on the macrosegregation is also discussed.

Combustion characteristics of TiO2/Al/C system

Abstract The formation of TiC-Al 2 O 3 composite powder was studied by a combustion reaction on the system TiO 2 /Al/C. The effects of the molar ratios of raw materials, compaction pressure and initial temperature of reactants on the products and combustion process were studied. The most important variable affecting the synthesis of TiC-Al 2 O 3 was the molar ratio of C and Al. The highest yield of TiC-Al 2 O 3 was obtained at the molar ratio of TiO 2 :Al:C=3.0:4.0:2.7∼3.0. The combustion temperature and the combustion velocity were increased with increasing preheating temperature. On the other hand, the cooling rate was decreased with increasing of preheating temperature. The cooling rate after completing the combustion was related to grain size of products. The grain size was increased with decreasing cooling rate.

Targeting of Mycobacterium tuberculosis Heparin-Binding Hemagglutinin to Mitochondria in Macrophages

Mycobacterium tuberculosis heparin-binding hemagglutinin (HBHA), a virulence factor involved in extrapulmonary dissemination and a strong diagnostic antigen against tuberculosis, is both surface-associated and secreted. The role of HBHA in macrophages during M. tuberculosis infection, however, is less well known. Here, we show that recombinant HBHA produced by Mycobacterium smegmatis effectively induces apoptosis in murine macrophages. DNA fragmentation, nuclear condensation, caspase activation, and poly (ADP-ribose) polymerase cleavage were observed in apoptotic macrophages treated with HBHA. Enhanced reactive oxygen species (ROS) production and Bax activation were essential for HBHA-induced apoptosis, as evidenced by a restoration of the viability of macrophages pretreated with N-acetylcysteine, a potent ROS scavenger, or transfected with Bax siRNA. HBHA is targeted to the mitochondrial compartment of HBHA-treated and M. tuberculosis-infected macrophages. Dissipation of the mitochondrial transmembrane potential (ΔΨm) and depletion of cytochrome c also occurred in both macrophages and isolated mitochondria treated with HBHA. Disruption of HBHA gene led to the restoration of ΔΨm impairment in infected macrophages, resulting in reduced apoptosis. Taken together, our data suggest that HBHA may act as a strong pathogenic factor to cause apoptosis of professional phagocytes infected with M. tuberculosis.

Rv0315, a novel immunostimulatory antigen of Mycobacterium tuberculosis , activates dendritic cells and drives Th1 immune responses

Tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) is one of the most deadly infectious diseases, with approximately two million people dying of TB annually. An effective therapeutic method for activating dendritic cells (DCs) and driving Th1 immune responses would improve host defenses and further the development of a TB vaccine. Given the importance of DC maturation in eliciting protective immunity against TB, we investigated whether Rv0315, a newly identified Mtb antigen, can prompt DC maturation. We found that Rv0315 functionally activated DCs by augmenting the expression of the co-stimulatory molecules CD80 and CD86 as well as MHC class I/II molecules. Moreover, it increased DC secretion of the pro-inflammatory cytokines IL-6, IL-1β, and TNF-α. Unlike LPS, however, Rv0315 induced the secretion of IL-12p70, but not IL-10. In addition, Rv0315-treated DCs accelerated the proliferation of CD4+ and CD8+ splenic T cells from Mtb-infected mice, with increased levels of IFN-γ, in syngeneic and allogeneic mixed lymphocyte reactions, indicating that Rv0315 contributes to Th1 polarization of the immune response. Importantly, both mitogen-activated protein kinases and nuclear factor κB signaling mediated the expression of DC surface markers and cytokines. Taken together, our results indicate that Rv0315 is a novel DC maturation-inducing antigen that drives T cell immune responses toward Th1 polarization, suggesting that Rv0315 plays a key role in determining the nature of the immune response to TB.

Sintering behavior of Al2O3-TiC composite powder prepared by SHS process

Al2O3-TiC composite powder was prepared by the self-propagating high-temperature synthesis (SHS) process, using TiO2, Al, and C powders as raw materials. The effects of keeping the TiO2:Al:C molar ratio fixed at 3:4:2.7 while varying the carbon sources and cooling time on the products were studied. The highest combustion temperature and combustion velocity were obtained at activated carbon. But, microstructure and mechanical properties of sintered Al2O3-TiC composite did not show any significant differences according to the carbon sources. Hot pressing was found to be very effective in hindering the formation of pore and obtaining a dense sintered body at 1650°C. The sintered body produced by hot-pressing was about 98.8% and 99.2% of the theoretical density for synthesized and commercial powder respectively.

Effect of current application methods on the preparation of Fe–Al intermetallic compounds by field-activated combustion synthesis

Abstract Pure FeAl intermetallic compound was prepared by the field-activated combustion synthesis (FACS) process. Effects of compaction pressure (150, 250, and 350 MPa) and particle size (−25, −80, and −325 mesh) on the characteristics of products were investigated. As the compaction pressure and electric field increased, the combustion temperature and velocity increased. The influences of different current application methods on the reaction in this system were investigated. In the absence of an electric field, the reaction could not sustain a steady combustion wave and was not completed. The reaction products were characterized by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy to determine the structures and compositions.

Characteristics of Al2O3–SiC composite powder prepared by the self-propagating high-temperature synthesis process and its sintering behavior

Abstract Al 2 O 3 –SiC composite powder was prepared by the self-propagating high-temperature synthesis (SHS) process, using SiO 2 , Al, and C powders as raw materials. The effects of keeping the SiO 2 :Al molar ratio fixed at 3:4 while varying the relative carbon amount, compaction pressure, initial temperature of reactants, and combustion process on the products were studied. SHS of the SiO 2 /Al/C system required preheating above 400°C, because of the low combustion temperature. It was found that, as a result of the combustion reaction, the purity of the final product was better than that of the reactants. The optimum molar ratio of SiO 2 :Al:C in the system was found to be 3:4:6. The free carbon was removed by roasting at 650°C for 30 min. Pressureless sintering was found to be very effective in hindering the disintegration of the specimen with a Al 2 O 3 –SiC powder bed and obtaining a dense sintered body at 1700°C. The sintered body produced by hot-pressing was about 98% of the relative density.

Synthesis of tungsten monocarbide by self-propagating high-temperature synthesis in the presence of an activative additive

Tungsten monocarbide was synthesized by Self-Propagating High-Temperature Synthesis. A SHS technique was developed in this work for W-C system characterized by a low adiabatic combustion temperature of 1000 K. Samples were synthesized by in combustion wave propagating along compacts of elemental tungsten, carbon and a highly exothermal mixture [Mg + (-C2F4-)n] as an activative additive under argon atomsphere of 1 atm. A quite high conversion rate was achieved at a combustion temperature of 2109 K. It is shown that in the presence of a small amount of (about 10 wt.%) the additive mixture acquires the capacity to burn and sustain the combustion front wave propagating. The lattic of tungsten monocarbide obtained was hexagonal and its particle size was 1 ∼ 2 μm. In the final product, MgF2 and asmall amount of W2C, both byproducts, were completely removed by acidic leaching. The purity of the tungsten monocarbide was 99% after leaching.