Effects Of Chemical Inhibition Research Articles

Effects of chemical inhibition of N-WASP, a critical regulator of actin polymerization on aqueous humor outflow through the conventional pathway

The integrity of actin cytoskeletal organization in aqueous humor outflow pathway is thought to play a critical role in modulation of aqueous humor outflow through the trabecular meshwork. Our understanding of the regulation of actin cytoskeletal dynamics in outflow pathway, however, is very limited. To explore the potential importance of Neural Wiskott–Aldrich syndrome protein (N-WASP), a critical regulator of actin polymerization/nucleation in aqueous humor outflow pathway, the effects of Wiskostatin, a selective pharmacological inhibitor of N-WASP, on aqueous humor outflow facility were evaluated using enucleated porcine eyes and a constant pressure perfusion system. Further, drug induced effects on actin cytoskeletal organization, cell adhesions, myosin II phosphorylation, matrix metalloproteinase (MMP) activity, and cytoskeletal protein profile in porcine trabecular meshwork (TM) cells were determined by immunofluorescence, zymography, and mass spectrometry. Aqueous humor outflow facility was increased significantly and progressively in the Wiskostatin perfused porcine eyes. The Wiskostatin perfused eyes appear to exhibit increased giant vacuoles in the inner wall of aqueous plexi and deformation of aqueous plexi. The Wiskostatin treated TM cells demonstrated extensive vacuoles in their cytosol, and both actin stress fibers and focal adhesions were decreased in a reversible manner. The drug-treated TM cells also revealed decreased myosin II and actin in the cytoskeletal enriched triton insoluble fraction but did not affect myosin II phosphorylation or MMP-2 activity. These data demonstrate that the chemical inhibition of N-WASP increases aqueous humor outflow facility in association with decreased actomyosin interaction and cell adhesive interactions revealing the importance of N-WASP in homeostasis of aqueous humor outflow.

Combining chemical genomics screens in yeast to reveal spectrum of effects of chemical inhibition of sphingolipid biosynthesis.

BackgroundSingle genome-wide screens for the effect of altered gene dosage on drug sensitivity in the model organism Saccharomyces cerevisiae provide only a partial picture of the mechanism of action of a drug.ResultsUsing the example of the tumor cell invasion inhibitor dihydromotuporamine C, we show that a more complete picture of drug action can be obtained by combining different chemical genomics approaches – analysis of the sensitivity of ρ0 cells lacking mitochondrial DNA, drug-induced haploinsufficiency, suppression of drug sensitivity by gene overexpression and chemical-genetic synthetic lethality screening using strains deleted of nonessential genes. Killing of yeast by this chemical requires a functional mitochondrial electron-transport chain and cytochrome c heme lyase function. However, we find that it does not require genes associated with programmed cell death in yeast. The chemical also inhibits endocytosis and intracellular vesicle trafficking and interferes with vacuolar acidification in yeast and in human cancer cells. These effects can all be ascribed to inhibition of sphingolipid biosynthesis by dihydromotuporamine C.ConclusionDespite their similar conceptual basis, namely altering drug sensitivity by modifying gene dosage, each of the screening approaches provided a distinct set of information that, when integrated, revealed a more complete picture of the mechanism of action of a drug on cells.

Cell-cycle Checkpoint Control and Radiosensitivity after Low-dose X-irradiation: Implications for IMRT

Low-dose hyper-radiosensitivity has been established in tumors and normal tissues. Our previous work has indicated the importance of a specific G2-phase cell cycle checkpoint in this response. After low-dose irradiation, this checkpoint fails to prevent a subset of damaged G2-phase cells from entering mitosis, which eventually leads to caspase 3-mediated apoptosis. Radiation doses above ∼0.3 Gy produce sufficient damage for complete checkpoint activation and repair induction. The purpose of the current study was to (1) define the complete dose and temporal response of the G2-checkpoint in normal fibroblasts, (2) determine the position of the checkpoint in the G2-phase of the cell cycle, (3) define the signaling pathways involved in this response and (4) investigate the effects of chemical inhibition of checkpoint function.

The cytotoxic effect of bromoenol lactone, a calcium-independent phospholipase A2 inhibitor, on rat cortical neurons in culture.

This study characterized the phospholipase A(2) (PLA(2)) activity in cerebral cortex of fetal rat brain and investigated effects of chemical inhibition of Ca(2+)-independent PLA(2) (iPLA(2)) on neurite outgrowth and cell development of cortical neurons in vitro. The PLA(2) activity in fetal brain was insensitive to a Ca(2+)-chelator EGTA and was significantly impaired by an iPLA(2) inhibitor, bromoenol lactone (BEL). Following treatment with BEL, cortical neurons showed acute loss of neurites and impaired cell body, which were clearly dose- and time-dependent. Nuclear staining revealed nuclear regression (shrinkage), but not fragmentation, in BEL-treated cells. The cytotoxic effect of BEL was additive with arachidonic acid (AA) and AA alone also induced neurite demise. BEL treatment resulted in increased production of prostaglandin E(2). Overall data suggest that iPLA(2), a primary PLA(2) isoform in cerebral cortex, displays a housekeeping role in development and neurite outgrowth in cortical neurons in vitro probably via maintaining phospholipid membrane remodeling rather than generating free fatty acids and lysophospholipids.

The effect of chemical inhibition of matrix metalloproteinases on the size of experimentally induced apical periodontitis

To determine the effect of matrix metalloproteinase (MMP) inhibition on periapical lesion formation in a rat model. The pulp chambers of mandibular fist molars of adult SD rats were exposed to be infected by oral microbes. The experimental group was fed 20 mg kg(-1) MMP-inhibitor chemically modified tetracycline-3 (CMT-3) daily in an oral gavage and the controls were fed the vehicle. After 2 and 4 weeks, the mandibles (n = 10 in both groups at both times) were radiographed, decalcified and subjected to histological analysis. Extension of necrosis in first molar distal root canals was measured from the histological sections, and periapical lesion sizes in the same roots were determined from radiographs and histological sections. Mann-Whitney U-test was used for the statistical analysis. There was a statistically significant difference in the extension of necrosis in root canals between 2 and 4 weeks in the control group (P < 0.05), but not with MMP inhibition. Radiographically, MMP inhibition increased the periapical lesion size by 70% and 34% after 2 and 4 weeks respectively (P < 0.05 in after 2 weeks). In histological measurements, lesion size increased with MMP inhibition by 26% and 8% after 2 and 4 weeks respectively. MMP inhibition affects pulpal and periapical inflammation, increasing the rate of spreading of necrosis in root canals and the rate of periapical lesion formation.

Chemical modulation of receptor signaling inhibits regenerative angiogenesis in adult zebrafish

We examined the role of angiogenesis and the need for receptor signaling using chemical inhibition of the vascular endothelial growth factor receptor in the adult zebrafish tail fin. Using a small-molecule inhibitor, we were able to exert precise control over blood vessel regeneration. An angiogenic limit to tissue regeneration was determined, as avascular tissue containing skin, pigment, neuronal axons and bone precursors could regenerate up to about 1 mm. This indicates that tissues can regenerate without direct interaction with endothelial cells and at a distance from blood supply. We also investigated whether the effects of chemical inhibition could be enhanced in zebrafish vascular mutants. We found that adult zebrafish, heterozygous for a mutation in the critical receptor effector phospholipase Cgamma1, show a greater sensitivity to chemical inhibition. This study illustrates the utility of the adult zebrafish as a new model system for receptor signaling and chemical biology.

The Necessity of Studying Chemical Reactions of the Clean Agent Heptafluoropropane in Fire Extinguishment

Halon-based products for gas protection systems against fire will be abandoned completely, probably in China by 2008. Clean agents with zero ozone depletion potential and low global warming potential now are actively being developed. One of the candidates is heptafluoropropane and total flooding systems based on it are starting to be widely used in computer rooms, switching facilities and many other facilities. However, the extinguishing mechanism of heptafluoropropane with afire is not well-understood. It is believed that physical flame cooling is the main mechanism. Heat will be absorbed efficiently from the flame reaction zone to reduce its temperature. Apart from flame cooling, whether there are chemical inhibition effects must be further investigated in order to give a better understanding on the extinguishing properties of the agent. Pointing out the importance of studying the associated gas-phase chemistry is the objective of this paper. Results in the literature will be briefly reviewed. In unfavourable cases, using a clean agent with a low capability to suppress a fire might generate more pollutants which damage the environment.

SUPPRESSION CHEMISTRY OF WATER MISTS ON DIFFUSIONAL FLAMES

It is well-known that fire suppression by water mist is mainly based on physical effects such as heat extraction through evaporation, oxygen displacement, and attenuation of thermal radiation. However, there might be chemical inhibition effects which are not clearly understood. Chemical kinetics associated with the interaction of water with flames should be studied, but the reaction chemistry depends on the flame to be suppressed. It would be very interesting to investigate the suppression chemistry of water mist on burning different fuels of polymers. Suppression chemistry of water mist on diffusion flames from burning different fuels will be reviewed first. Homogeneous interaction of water with gas fuel in the combustion will then be discussed. Heterogeneous oxidation of carbon in the existence of water will be briefly introduced. The kinetics and mechanisms of selected reactions involving hydrogen (H), carbon monoxide (CO), carbon-based fuels (C), and small hydrocarbons such as methane (CH4) will also be discussed. Those are considered key combustion reactions which can provide useful information for understanding burning polymers. Note that polymeric materials have been widely used in modern buildings. Fire safety associated with burning plastics is a great concern. In such interaction reactions, water is taken as interacting with the flame by converting the oxygen (O) radicals to hydroxyl groups (OH). These products would have direct involvement in the water-gas reaction system by acting as efficient collision partners in the chemical kinetics of the combustion reactions.

PARP-1, PARP-2, and the cellular response to low doses of ionizing radiation

Purpose Poly(ADP-ribose) polymerase-1 (PARP-1) is rapidly and directly activated by single-strand breaks and is required for efficient base excision repair. These properties indicate that inhibition of PARP-1 might enhance the cellular response to low doses of radiation. We tested the effect of chemical inhibition of PARP-1 on low-dose clonogenic survival in a number of cell lines and the low-dose radiation response of a PARP-1 knockout murine cell line. Methods and materials Clonogenic cell survival of V79-379A and CHO-K1 hamster fibroblasts, T98G and U373-MG human glioma cells, and 3T3 mouse embryo fibroblast PARP-1 knockout cells was measured using a precise flow cytometry-based plating assay. Chemical inhibitors of PARP enzymes were tested for their effect on clonogenic survival after a range of ionizing radiation doses. Results Chemical inhibition of PARP activity induced marked radiosensitization of V79, CHO, and exponentially growing T98G cells in the 0.05–0.3-Gy range. This effect was not seen in U373 cells or in confluent T98G populations. Low-dose radiosensitization was not apparent in PARP-1 knockout cells. Conclusion Low-dose radiosensitization of actively dividing tumor cells by PARP-1 inhibitors suggests that they may have a role in enhancing the efficacy of ultrafractionated or low-dose-rate radiotherapy regimens. We hypothesize that PARP-2 compensates for the absence of PARP-1 in the knockout cell line.

The Structure of Laminar Diffusion Flames Inhibited with CF3Br

Abstract The paper presents a study of the chemical inhibition effects of CF3Br (halon-1301) in laminar diffusion flames of CH4-air and CO/H2/N2 fuels. Comparisons are made between measurements and computations for flames of pure fuel, fuel premixed with CF3Br and for flames of pure fuel with the surrounding air premixed with CF3Br. The measurements of temperature and the concentration of many stable species including HF, H Br and CF3Br as well as the hydroxyl radical, OH are made in axisymmetric flames using the Raman-Rayleigh-LIF technique. Calculations are performed for laminar counterflow nonpremixed flames using complex chemistry and detailed transport properties. It is found that the addition of halon-1301 increases the peak temperature of the flame and causes little change in the concentrations of stable species. However, the minor species and flame radicals are significantly affected. The rate of decomposition of CF3Br is not well predicted and significant discrepancy exists in the computations of...

Responses of blue-green and green algae to streptomycin in unialgal and paired culture

Streptomycin sulfate prevented growth of six blue-green algae at concentrations (0.09 to 0.86 mg/l) substantially lower than needed to prevent growth of 7 of 8 green algae tested. Chlorella vulgaris, Scenedesmus obliquus and Ulothrix sp. grew in active streptomycin concentrations less than 21 mg/l, while Chlamydomonas reinhardtii growth was prevented at concentrations of 0.66 mg/l. Algal growth in sublethal concentrations of streptomycin was slowed or delayed, and the maximum density attained by several species was decreased. These data suggest that attempts to select ‘representative’ species for toxicity testing may have mixed success: any blue-green alga would be a suitable representative of Cyanophyta with respect to streptomycin, but no single green alga would adequately represent the wide range of response to streptomycin seen among the Chlorophyta species tested. To test for interactions between competition and chemical inhibition, paired cultures of S. obliquus with Anabaena cylindrica, Ankistrodesmus sp., C. vulgaris and Selenastrum capricornutum were observed with and without 6.6 mg/l streptomycin. The outcome of competition was consistent with predictions based on single-species assays, where major differences in chemical sensitivity were present, although significant interactions were observed. S. obliquus populations when treated with streptomycin were competitively superior to A. cylindrica and S. capricornutum. Significant interactions between competition and streptomycin treatement were also observed for paired cultures of C. vulgaris and S. obliquus; neither population fit the model of additive effects of chemical inhibition and competition.

Extinction phenomenon of premixed flames with alkali metal compounds

In order to investigate the flame suppression mechanism of alkali metal salts, ultrafine powders of these salts with diameters less than 1 μm were introduced into premixed flames in the form of mists of their water solutions. Premixed flames inhibited by the mist suddenly blew offif the mist density was increased beyond a critical value. This sudden extinction of flames was peculiar to alkali metal salts and it was not observed for other inhibitors. From the existence of the extinction condition, the time necessary for the salts to have a chemical inhibition effect was found to be 10 ms at 1200K and 0.5 ms at 1800K. This critical time was found to correspond to the decomposition time of the salts. The result shows that alkali metal compounds must stay in the flames longer than this critical time in order to work as chemical flame suppressants. If the residence time in flames is less than the critical time, the inhibition effect of the powders will be purely thermal, especially for powders with larger diameters. This model for flame suppression of alkali metal compounds can explain many contradictory results in experimental studies reported previously.

Flame retardant effects of CF 3Br and NaHCO 3

Using theoretical results on heterogeneous flame suppression, the thermal and chemical inhibition effects on premixed flames were investigated. First, the chemical effectiveness of CF 3Br was experimentally measured and obtained in an Arrhenius form for the overall inhibition reaction. Second, the chemical effectiveness of NaHCO 3 powders in the gas phase was assumed from that of CF 3Br. The theory then gave flame speed response curves with respect to the addition of NaHCO 3 powders in a premixed H 2O 2N 2 flame, and predicted the amounts necessary to extinguish the flame. The decomposition of condensed materials in the preheat zone of lames was also formulated in order to evaluate the decomposition rate of particles.

A study on thermal and chemical effects of heterogeneous flame suppressants

An asymptotic analysis involving the limit of large activation energy is presented for the study of thermal and chemical inhibition effects on premixed flames by heterogeneous flame suppressants. A formulation analogous to that for heterogeneous laminar flame is employed for evaluating the thermal effect, and extended to include the chemical effect in flame inhibition of decomposed particles or vaporized sprays. The propagation velocity of inhibited flames depends on the loading parameter γ 1, the particle size parameter γ 2, the nondimensional decomposition or latent heat of materials γ 3, the chemical effectiveness γ 4, and the decomposition rate parameter ζ 0 ∗ . The results for thermal inhibition ( γ 4 → 0) show that the response curve of the dependence of flame speed on parameters γ 1 or γ 2 has an S-shaped variation for flame suppressants satisfying γ 1 > γ 1 ∗ and γ 2 < γ 2 ∗ , which correspond to a sufficient concentration of powders consisting of large particles. A slow decomposition rate, ζ 0 ∗ → 1 , is essential for this S-shaped variation of flame speed. The results also show that the chemical effect on flame speeds appears as a virtual increase in the particle size parameter γ 2, by the factor 1 1−γ 1(1−ζ 0 ∗)γ 4 , if the relative rate γ 4 of the chain-breaking reaction by gaseous inhibitors measured at the flame temperature is introduced.

Comparison of experiments and theory on heterogeneous flame suppressants

Experimental results obtained for heterogeneous flame suppression were compared with theoretical results. Flame propagation velocities inhibited by Al 2 O 3 and NaHCO 3 powders were measured by the burner method, and the flame retardant phenomenon was investigated. The results show that: o (1) The experimental results for Al 2 O 3 powders in H 2 −O 2 −N 2 flames support the thermalinhibition theory. Flame speed inhibited by large particles varies along the upper branch solution of the triple-valued function, and the flame suddenly extinguishes at the nose point of the upper branch. (2) Although the flame retardant effect of NaHCO 3 is several times as great as that of Al 2 O 3 , the effectiveness can be explained mostly by the thermal inhibition effect including the decomposition heat of NaHCO 3 . (3) Some behaviors in experimental results can not be clarified only by the thermal effect.Possibilities of the chemical inhibition effect are discussed, although it has not a dominant role in the present flame retardant experiment.