Synergistic Enhanced Thermal Conductivity and Crack Resistance of Reactor Epoxy Insulation with Boron Nitride Nanosheets and Multiwalled Carbon Nanotubes.

Epoxy composites with high thermal conductivity, excellent dielectric, and mechanical properties are very promising for solving epoxy cracking faults in reactors and for extending their service life. In this work, we report on epoxy composites enhanced by ternary fillers of boron nitride nanosheets (BNNSs), multiwalled carbon nanotubes (MWCNTs), and silica (SiO2) nanoparticles. The obtained BNNSs/MWCNTs/SiO2/epoxy composites exhibit a high thermal conductivity of 0.9327 W m-1 K-1, which is more than 4-fold higher than that of pure epoxy. In addition, the resultant composites present an improved mechanical strength (from 2.7% of epoxy to 3.47% of composites), low dielectric constant (4.6), and low dielectric loss (0.02). It is believed that the integration of multifunctional properties into epoxy composites provides guidance for optimizing the design of high-performance materials.

Suppressing stimulated Raman scattering in kW-level continuous-wave MOPA fiber laser based on long-period fiber gratings.

Two long-period fiber gratings (LPFGs) used to separately suppress the stimulated-Raman-scattering (SRS) in the seed and amplifier of kW-level continuous-wave (CW) MOPA fiber laser are developed in this paper. A process that combines constant-low-temperature and dynamic-high-temperature annealing was employed to reduce the thermal slopes of 10/130 µm (diameter of core/cladding fiber) and 14/250 LPFGs, used in the seed and amplifier respectively, from 0.48 °C/W to 0.04 °C/W and from 0.53 °C/W to 0.038 °C/W. We also proposed a reduced-sensitivity packaging method to effectively reduce the influence of axial-stress, bending, and environmental temperature on LPFGs. Further, we established a kW-level CW MOPA system to test SRS suppression performance of the LPFGs. Experimental results demonstrated that the SRS suppression ratios of the 10/130 and 14/250 LPFGs exceed 97.0% and 99.6%, respectively.

Metabolism and disposition of ABT-894, a novel α4ß2 neuronal acetylcholine receptor agonist, in mice and monkeys.

1. Metabolism and disposition of ABT-894 was investigated in hepatocytes, in mice and monkeys receiving [(14)C]ABT-894. 2. In hepatocytes, turnover rate of ABT-894 was slow in all species with more than 90% of parent remaining. M3 (carbamoyl glucuronide) and M6 (mono-oxidation) were detected across species. 3. ABT-894 showed species-specific disposition profiles. ABT-894 was primarily eliminated by renal secretion in mice. Whereas, monkey mainly cleared ABT-894 metabolically. 4. ABT-894 underwent two primary routes of metabolism in monkeys: N-carbamoyl glucuronidation to form M3 and oxidation product M1. M3 was the major metabolite in monkey excreta. M3 was observed in mice urine. Circulating levels of M3 in terms of M3/ABT-894 ratios were essentially absent in mice, but were high in monkeys. 5. Understanding the species difference in the clearance mechanism is the key to the accurate projection of the human clearance and preclinical safety assessment. Lack of species difference in the metabolism of ABT-894 in hepatocytes certainly creates a challenge in predicting its metabolism and pharmacokinetics in human. Based on available metabolism and pharmacokinetic data of ABT-894 in human, monkey is the preferred species in predicting human clearance since it presents a similar clearance mechanism from that observed in human.

Species-dependent metabolism of a novel selective α7 neuronal acetylcholine receptor agonist ABT-107.

Metabolism of ABT-107 was investigated in in vitro hepatic systems, in rat and monkey receiving [¹4C]ABT-107, and in vivo plasma in rat, dog, monkey and human. In in vitro hepatic systems, ABT-107 was primarily cleared via oxidative metabolism, and proceeded via two parallel pathways. Pathway 1, ABT-107 was oxidized at the nitrogen of quinuclidine moiety to form M1. Pathway 2, oxidation occurred at indole-containing moiety to form M2. Metabolism via N-oxidation was predominant in dog and rat, while in monkey and human, metabolism proceeded primarily via oxidation of indole-containing moiety. ABT-107 was extensively metabolized in vivo in rat and monkey. M1 was primarily found in rat urine and bile; whereas, M2 was the major metabolite in monkey urine and feces. M1 was the predominant circulating metabolite in dog and rat. M2 was the primary circulating metabolite in monkey and human. Enzymatic studies suggested M1 formation was primarily mediated by renal FMO1. CYP3A4, 1A2, 2J2 and 2D6 were primary enzymes catalyzing M2 formation. Biotransformation of ABT-107 in human and monkey is markedly different from that in dog and rat, suggesting that monkey is an appropriate model for predicting human biotransformation and toxicology of ABT-107.

Thienopyridine ureas as dual inhibitors of the VEGF and Aurora kinase families.

In an effort to identify multi-targeted kinase inhibitors with a novel spectrum of kinase activity, a screen of Abbott proprietary KDR inhibitors against a broad panel of kinases was conducted and revealed a series of thienopyridine ureas with promising activity against the Aurora kinases. Modification of the diphenyl urea and C7 moiety of these compounds provided potent inhibitors with good pharmacokinetic profiles that were efficacious in mouse tumor models after oral dosing. Compound 2 (ABT-348) of this series is currently undergoing Phase I clinical trials in solid and hematological cancer populations.

Lys842 in neuronal nitric-oxide synthase enables the autoinhibitory insert to antagonize calmodulin binding, increase FMN shielding, and suppress interflavin electron transfer.

Neuronal nitric-oxide synthase (nNOS) contains a unique autoinhibitory insert (AI) in its FMN subdomain that represses nNOS reductase activities and controls the calcium sensitivity of calmodulin (CaM) binding to nNOS. How the AI does this is unclear. A conserved charged residue (Lys(842)) lies within a putative CaM binding helix in the middle of the AI. We investigated its role by substituting residues that neutralize (Ala) or reverse (Glu) the charge at Lys(842). Compared with wild type nNOS, the mutant enzymes had greater cytochrome c reductase and NADPH oxidase activities in the CaM-free state, were able to bind CaM at lower calcium concentration, and had lower rates of heme reduction and NO synthesis in one case (K842A). Moreover, stopped-flow spectrophotometric experiments with the nNOS reductase domain indicate that the CaM-free mutants had faster flavin reduction kinetics and had less shielding of their FMN subdomains compared with wild type and no longer increased their level of FMN shielding in response to NADPH binding. Thus, Lys(842) is critical for the known functions of the AI and also enables two additional functions of the AI as newly identified here: suppression of electron transfer to FMN and control of the conformational equilibrium of the nNOS reductase domain. Its effect on the conformational equilibrium probably explains suppression of catalysis by the AI.

PTEN functions to 'prioritize' chemotactic cues and prevent 'distraction' in migrating neutrophils.

Neutrophils encounter and 'prioritize' many chemoattractants in their pursuit of bacteria. Here we tested the possibility that the phosphatase PTEN is responsible for the prioritization of chemoattractants. Neutrophils induced chemotaxis by two separate pathways, the phosphatidylinositol-3-OH kinase (PI(3)K) phosphatase and tensin homolog (PTEN) pathway, and the p38 mitogen-activated protein kinase pathway, with the p38 pathway dominating over the PI(3)K pathway. Pten(-/-) neutrophils could not prioritize chemoattractants and were 'distracted' by chemokines when moving toward bacterial chemoattractants. In opposing gradients, PTEN became distributed throughout the cell circumference, which inhibited all PI(3)K activity, thus permitting 'preferential' migration toward bacterial products via phospholipase A(2) and p38. Such prioritization was defective in Pten(-/-) neutrophils, which resulted in defective bacterial clearance in vivo. Our data identify a PTEN-dependent mechanism in neutrophils to prioritize, 'triage' and integrate responses to multiple chemotactic cues.

Pharmacokinetic enhancement of the hepatitis C virus protease inhibitors VX-950 and SCH 503034 by co-dosing with ritonavir.

Inhibitors of hepatitis C virus (HCV) protease have shown marked antiviral activity in short-term clinical studies in HCV-infected individuals. The interaction of the investigational HCV protease inhibitors VX-950 and SCH 503034 with ritonavir, a potent inhibitor of cytochrome P450 3A, was studied in vitro and in vivo. In rat and human liver microsomes, the metabolism of VX-950 and SCH 503034 was strongly inhibited by the presence of 4 microM ritonavir. Upon co-dosing either VX-950 or SCH 503034 with ritonavir in rats, plasma exposure of the HCV protease inhibitors was increased by > 15-fold, and plasma concentrations 8 h after dosing were increased by > 50-fold. A human pharmacokinetic model of VX-950 co-administered with low-dose ritonavir suggested that improved efficacy and/or dosing convenience may be feasible by pharmacokinetic enhancement with ritonavir.

Human neuronal nitric oxide synthase can catalyze one-electron reduction of adriamycin: role of flavin domain.

We have analyzed the mechanism of one-electron reduction of adriamycin (Adr) using recombinant full-length human neuronal nitric-oxide synthase and its flavin domains. Both enzymes catalyzed aerobic NADPH oxidation in the presence of Adr. Calcium/calmodulin (Ca(2+)/CaM) stimulated the NADPH oxidation of Adr. In the presence or absence of Ca(2+)/CaM, the flavin semiquinone radical species were major intermediates observed during the oxidation of the reduced enzyme by Adr. The FAD-NADPH binding domain did not significantly catalyze the reduction of Adr. Neither the FAD semiquinone (FADH*) nor the air-stable semiquinone (FAD-FMNH*) reacted rapidly with Adr. These data indicate that the fully reduced species of FMN (FMNH(2)) donates one electron to Adr, and that the rate of Adr reduction is stimulated by a rapid electron exchange between the two flavins in the presence of Ca(2+)/CaM. Based on these findings, we propose a role for the FAD-FMN pair in the one-electron reduction of Adr.

Mechanistic studies on the intramolecular one-electron transfer between the two flavins in the human neuronal nitric-oxide synthase and inducible nitric-oxide synthase flavin domains.

Neuronal nitric-oxide synthase (nNOS) differs from inducible NOS (iNOS) in both its dependence on the intracellular Ca2+ concentration and the production rate of NO. To investigate what difference(s) exist between the two NOS flavin domains at the electron transfer level, we isolated the recombinant human NOS flavin domains, which were co-expressed with human calmodulin (CaM). The flavin semiquinones, FADH* and FMNH*, in both NOSs participate in the regulation of one-electron transfer within the flavin domain. Each semiquinone can be identified by a characteristic absorption peak at 520 nm (Guan, Z.-W., and Iyanagi, T. (2003) Arch. Biochem. Biophys. 412, 65-76). NADPH reduction of the FAD and FMN redox centers by the CaM-bound flavin domains was studied by stopped-flow and rapid scan spectrometry. Reduction of the air-stable semiquinone (FAD-FMNH*) of both domains with NADPH showed that the extent of conversion of FADH2/FMNH* to FADH*/FMNH2 in the iNOS flavin domain was greater than that of the nNOS flavin domain. The reduction of both oxidized domains (FAD-FMN) with NADPH resulted in the initial formation of a small amount of disemiquinone, which then decayed. The rate of intramolecular electron transfer between the two flavins in the iNOS flavin domain was faster than that of the nNOS flavin domain. In addition, the formation of a mixture of the two- and four-electron-reduced states in the presence of excess NADPH was different for the two NOS flavin domains. The data indicate a more favorable formation of the active intermediate FMNH2 in the iNOS flavin domain.

Electron transfer is activated by calmodulin in the flavin domain of human neuronal nitric oxide synthase.

The objective of this study was to clarify the mechanism of electron transfer in the human neuronal nitric oxide synthase (nNOS) flavin domain using the recombinant human nNOS flavin domains, the FAD/NADPH domain (contains FAD- and NADPH-binding sites), and the FAD/FMN domain (the flavin domain including a calmodulin-binding site). The reduction by NADPH of the two domains was studied by rapid-mixing, stopped-flow spectroscopy. For the FAD/NADPH domain, the results indicate that FAD is reduced by NADPH to generate the two-electron-reduced form (FADH(2)) and the reoxidation of the reduced FAD proceeds via a neutral (blue) semiquinone with molecular oxygen or ferricyanide, indicating that the reduced FAD is oxidized in two successive one-electron steps. The neutral (blue) semiquinone form, as an intermediate in the air-oxidation, was unstable in the presence of O(2). The purified FAD/NADPH domain prepared under our experimental conditions was activated by NADP(+) but not NAD(+). These results indicate that this domain exists in two states; an active state and a resting state, and the enzyme in the resting state can be activated by NADP(+). For the FAD/FMN domain, the reduction of the FAD-FMN pair of the oxidized enzyme with NADPH proceeded by both one-electron equivalent and two-electron equivalent mechanisms. The formation of semiquinones from the FAD-FMN pair was greatly increased in the presence of Ca(2+)/CaM. The air-stable semiquinone form, FAD-FMNH(.), was further rapidly reduced by NADPH with an increase at 520 nm, which is a characteristic peak of the FAD semiquinone. Results presented here indicate that intramolecular one-electron transfer from FAD to FMN is activated by the binding of Ca(2+)/CaM.