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Probable Mechanism (probable + mechanism)
Selected AbstractsDietary iron overload in the African and hepatocellular carcinomaLIVER INTERNATIONAL, Issue 6 2007Michael C. Kew Abstract Dietary iron overload occurs commonly in parts of sub-Saharan Africa. It results from the consumption of large volumes of traditional beer that is home-brewed in iron pots or drums and consequently has a high iron content. The liver becomes iron overloaded and may develop portal fibrosis or, less often, cirrhosis. A genetic predisposition to the condition has been suggested, but no putative gene has yet been identified. Although originally believed not to cause hepatocellular carcinoma, recent case,control studies have shown African Blacks with dietary iron overload to be at increased risk for the tumour and a causal association has been confirmed in an animal model. The mechanisms of iron-induced malignant transformation are yet to be fully characterised, but the close association between cirrhosis and hepatocellular carcinoma in patients with hereditary haemochromatosis and the lesser association in those with dietary iron overload, suggests that chronic necroinflammatory hepatic disease contributes to the malignant transformation. Increased hepatic iron may, however, also be directly carcinogenic. Probable mechanisms include the generation of reactive oxygen intermediates and the resultant chronic oxidative stress that damages hepatocytes and proteins, causes lipid peroxidation, and induces strand breaks, DNA unwinding, and mutations in tumour-suppressor genes and critical DNA repair genes. [source] Reaction kinetics for the degradation of phenol and chlorinated phenols using Fenton's reagentENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 1 2006Asim K. De Abstract Fenton's reaction is an advanced treatment technology often used for the removal of hazardous and refractory organic compounds from industrial wastewaters. It can effectively be used to degrade phenol and chlorophenols. The initial contaminant concentrations as well as the concentration of hydrogen peroxide and ferrous ions in aqueous solution have a significant effect on the effective degradation of contaminants. For a particular concentration of initial substrate in solution there should be an optimum level of ferrous ion concentration in the reaction medium. Based on experimental observations, a probable mechanism for Fenton's degradation kinetics has been proposed and a rate equation developed. From the rate expression, OH· radical reaction rate constants for the degradation of three compounds,phenol and o- and p-chlorophenols,in Fenton reaction were calculated to have values of 2.53 × 107, 2.38 × 107, and 2.45 × 107 m3 mol,1 s,1, respectively. © 2005 American Institute of Chemical Engineers Environ Prog, 2005 [source] Postictal Central Apnea as a Cause of SUDEP: Evidence From Near-SUDEP IncidentEPILEPSIA, Issue 11 2000Elson L. So Summary: While undergoing video-EEG monitoring, a 20-year-old woman had a 56-second convulsive seizure, after which she developed persistent apnea. The rhythm of the electrocardiogram complexes was unimpaired for approximately 10 seconds, after which it gradually and progressively slowed until it stopped 57 seconds later. Evaluation after successful cardiorespiratory resuscitation showed no evidence of airway obstruction or pulmonary edema. The patient had a previous cardio-respiratory arrest after a complex partial seizure without secondary generalization. Although epileptic seizures are known to be potentially arrhythmogenic to the heart, our observations strongly suggest that one probable mechanism of sudden unexplained death in epilepsy is the marked central suppression of respiratory activity after seizures. [source] Electro-Oxidation of Methanol and Ethanol on Poly(3,4-Ethylenedioxythiophene) with Dispersed Pt, Pt + Sn, and Pt + Pb Particles,FUEL CELLS, Issue 1-2 2003S. Biallozor Abstract The influence of tin and lead additives on the catalytic activity of platinum particles dispersed on a poly(3,4-dioxyethylenethiophene) (PEDT) layer deposited on gold or steel towards anodic oxidation of methanol and ethanol was studied. It was found that these additives increase the rate of anodic oxidation of both alcohols. It was also found that the electro-catalytic properties of PEDT depend on the kind of support used for its deposition. The authors have shown that these additives (Pb and Sn) increase the rate of anodic oxidation of both alcohols on platinum deposited on PEDT, but tin was evidently more effective than lead. In the presence of Sn, the steady-state current density of methanol oxidation increases about 100 times, while Pb only promotes the platinum catalyst activity by about 2 times. In the authors opinion the most probable mechanism for the tin promotion effect seems to be a homogenous catalytic reaction with the participation of the Sn (IV) and Sn (II) ions as mediators. [source] The concept of the taxon cycle in biogeographyGLOBAL ECOLOGY, Issue 5 2002Robert E. Ricklefs Abstract Taxon cycles are sequential phases of expansion and contraction of the ranges of species, associated generally with shifts in ecological distribution. The important contribution of the taxon cycle to biogeographical analysis is its emphasis on evolutionary and ecological interactions among colonizing and resident species, which influence their extinction dynamics and establish patterns of geographical distribution. Taxon cycles were inferred originally from the distribution of species across island archipelagos, where a correlation was noted between gaps in island occupancy and the degree of phenotypic differentiation. This pattern implied that phases of colonization were followed by range contraction, while endemic Antillean species that were undifferentiated between islands suggested secondary expansion and the beginning of a new cycle. This interpretation was met with scepticism, but reconstruction of phylogenetic relationships from gene sequences has now permitted us to characterize taxon cycles in Lesser Antillean birds. The relative timing of phases of the cycle can be deduced from genetic divergence between island populations. We have found that taxon cycles have periods in the order of 106 years and that cycles in different lineages occur independently of each other and independently of Pleistocene climate cycles. Individual island populations may persist for several millions of years on the larger islands of the Lesser Antilles; occasional expansion phases lead to the replacement of island populations that have disappeared, thus reducing the archipelago-wide rate of extinction to nil. What drives taxon cycles is unknown, but we speculate that they may be caused by co-evolution with enemy populations, and a probable mechanism would involve infrequent mutations influencing parasite virulence and avian host disease resistance. Taxon cycles undoubtedly occur on continents, but the geographical configuration of island archipelagos reveals more clearly their presence and invites their study. [source] A convenient one-pot synthesis of 1,2-azaphospholanium saltsHETEROATOM CHEMISTRY, Issue 7 2003Inga M. Aladzheva A novel facile one-pot synthesis of the 1,2-azaphospholanes by intramolecular alkylation of 3-halopropyl amides of tricoordinate phosphorus has been suggested. Using this method, a series of the differently N-substituted 1,2-azaphospholanium salts were synthesized. 3-Aminopropylphosphine oxides were obtained by hydrolysis of the salts. A probable mechanism of the 1,2-azaphospholanium salts formation is discussed. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:596,602, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10209 [source] Effects and probable mechanisms of electroacupuncture at the Zusanli point on upper gastrointestinal motility in rabbitsJOURNAL OF GASTROENTEROLOGY AND HEPATOLOGY, Issue 10 2007Wei-Xin Niu Abstract Background and Aim:, The purposes of this study were to investigate the regulative effect of acupuncture on gastrointestinal motility in rabbits and to explore the probable mechanism of electroacupuncture. Methods:, The experiment was performed on 30 rabbits implanted with three pairs of electrodes, which were equally divided into three groups: the control group, the Zusanli group, and the non-acupuncture point group. The gastrointestinal myoelectrical activity of each conscious rabbit was recorded when acupuncture was applied. Motilin in plasma, cholecystokinin (CCK) in serum, the activity of acetylcholine esterase, nitric oxide synthase (NOS), and the vesicle of nerve endings in the stomach tissue and jejunum were investigated. Results:, It was found that electroacupuncture did not exert much influence on the slow wave of gastrointestinal myoelectrical activity, but significantly increased the number and amplitude of spikes. In the Zusanli group, the concentration of motilin and CCK was much higher at the post-acupuncture stage than at the pre-acupuncture stage. Electroacupuncture significantly enhanced the activity of acetylcholine esterase. Moreover, we found out that in the Zusanli group, the number of vesicles without granula was significantly fewer than in the control group. The activity of NOS was less in the Zusanli group than in the control group. Conclusions:, Acupuncture may enhance the gastrointestinal myoelectrical activity of conscious rabbits. The cholinergic nerve, nitric oxide, motilin, and CCK may contribute to acupuncture mechanisms. [source] Effect of solvent on the inversion of pyramidal sulfonium and selenonium compoundsJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 4 2001Andreas Wiegrefe Abstract The effects of temperature and solvent on the cis,trans equilibrium and isomerization rates of different cyclic sulfonium and selenonium compounds were investigated by 1H NMR spectroscopy. A non-dissociative process was considered to be the most probable mechanism for inversion of configuration. While the temperature had no apparent effect on the equilibrium, in which the trans -diastereoisomer dominated in all cases, changing the solvent from dimethylformamide to acetonitrile and to water led to increasing amounts of the cis -diastereoisomer. Additionally, the rate of stereomutation of the thiolanium compound was slowed by a factor of 2 and that of the selenolanium compound by a factor of 85. While the pyramidal (vertex) inversion is the most probable mechanism for the sulfonium compounds investigated, some evidence is presented that indicates that the selenonium compound could isomerize via an edge inversion mechanism. Copyright © 2001 John Wiley & Sons, Ltd. [source] Peripheral Subcutaneous Neurostimulation in the Management of Neuropathic Pain: Five Case ReportsNEUROMODULATION, Issue 2 2009Claudio Reverberi MD, FIPP ABSTRACT Introduction., Spinal cord stimulation (SCS) is an effective treatment option for neuropathic pain. However, because of the obvious procedural issues, SCS is unable to reach certain areas, such as the face, thorax, coccyx, the cervico-dorsal and lumbar areas, and the sacral, abdominal, and inguinal regions. On the other hand, these areas are easily reached by subcutaneous field stimulation. Methodology., We report the analgesic results, using a visual analog scale (VAS), of five patients with neuropathic pain treated with subcutaneous field stimulation to the area. We also discuss the probable mechanism of action, and highlight the technical issues inherent to this approach. Results., Significant pain reduction and reduction in analgesic medication were reported in all patients during the study period, with VAS scores consistently lowered by more than 50% from baseline levels. As a result of pain reduction, the patients' quality of life improved. There were no adverse events reported except for early electrode array displacement in two of our patients. Conclusion., When SCS is not appropriate for certain neuropathic pain syndromes, subcutaneous field stimulation may be used with some degree of efficacy. [source] Synthesis of new superhydrophobic nanosilica and investigation of their performance in reinforcement of polysiloxanePOLYMER COMPOSITES, Issue 9 2010XianLi Fang We reported a new facile method to synthesize superhydrophobic nanosilica using glycidoxypropyltrimethoxysilane and dodecylamine as treatment agents. Also, we systemically investigate their performance in reinforcement of poly(dimethylsiloxane) (PDMS) rubber. Fourier transform infrared spectrum, contact angle (CA) and thermogravimetric analysis (TGA) measurements were used to characterize the modified nanosilica. Results show that the inherent hydrophilicity of parent nanosilica surface can be greatly altered through this modification method. The CA of as-prepared superhydrophobic nanosilica can reach 160.2°. The properties of as-prepared modified nanosilica-filled PDMS composites were systemically investigated by dynamic rheological test, scanning electron microscopy, TGA, dynamic mechanical analysis. These as-prepared superhydrophobic nanosilica exhibit uniform dispersion in the PDMS matrix, and their composites also show good mechanical properties and distinct advantage on thermal stability compared with those of the pure silica-filled PDMS composites. Also described is the probable mechanism for the reinforcement of as-prepared superhydrophobic nanosilica-filled PDMS. POLYM. COMPOS., 31:1628,1636, 2010. © 2009 Society of Plastics Engineers [source] Possible human chimera detected prenatally after in vitro fertilization: a case reportPRENATAL DIAGNOSIS, Issue 11 2003B. Simon-Bouy Abstract Background Chimerism is the coexistence of more than one cell line in an individual, due to the fusion of originally separate zygotes. It has been very rarely described in humans. Methods A 36-year-old woman who was referred for in vitro fertilization (IVF) for unexplained infertility had three embryos transferred. Results Four weeks and five days after the transfer, ultrasound examination detected a single fetus in the uterus. Ultrasound examination at 17 weeks for metrorrhagia showed severe intrauterine growth retardation. Amniocentesis revealed a mixture of 46,XY and 46,XX clones. Histopathologic examination showed a dysmorphic fetus with female phenotype and severe growth retardation. Conclusions Although demonstration by fingerprinting has not been possible, fusion of two of the three transferred embryos (one male and one female) seems to be the most probable mechanism that could explain both cytogenetic and histopathologic observations. No chimera has yet been described after IVF. It would be interesting to collect any such observations from other IVF centers. Copyright © 2003 John Wiley & Sons, Ltd. [source] A Novel Point Variant in NTRK3, R645C, Suggests a Role of this Gene in the Pathogenesis of Hirschsprung DiseaseANNALS OF HUMAN GENETICS, Issue 1 2009R. M. Fernández Summary Hirschsprung disease (HSCR) is a developmental disorder characterized by the absence of ganglion cells in the myenteric and submucosal plexuses due to a defect in the migration process of neural crest neuroblasts. Manifestation of the disease has been linked to the dysfunction of two principal signalling pathways involved in the enteric nervous system (ENS) formation: the RET-GDNF and the EDN3-EDNRB receptor systems. However, the NTF3/NTRK3 signalling pathway plays an essential role in the development of the ENS suggesting a potential role for those genes in the pathogenesis of HSCR. We have sought to evaluate the candidature of the NTRK3 gene, which encodes the TrkC receptor, as a susceptibility gene for Hirschsprung disease. Using dHPLC technology we have screened the NTRK3 coding region in 143 Spanish HSCR patients. A total of four previously described polymorphisms and 12 novel sequence variants were detected. Of note, the novel R645C mutation was detected in 2 affected siblings of a HSCR family also carrying a RET splicing mutation. Using bioinformatics tools we observed that the presence of an additional cysteine residue might implicate structural alterations in the mutated protein. We propose haploinsufficiency as the most probable mechanism for the NTRK3 R645C mutation. NTRK3 and RET mutations in this family only appear together in the HSCR patients, suggesting that they per se are necessary but not sufficient to produce the phenotype. In addition, it is quite probable that the contribution of other still unidentified modifier genes, may be responsible for the different phenotypes (length of aganglionosis) in the two affected members. [source] Methylation of tin(II) by methyl iodide: influences of different environmental factors on the efficiency and reaction kineticsAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 3 2006Chen Baowei Abstract The methylation reaction of Sn(II) with methyl iodide (MeI) in water has been studied using sensitive GC-QSIL-FPD technology. The pH value, amount of MeI and salinity (S) are the three important factors that influence the methylation reaction in an aquatic environment. In all experiments, monomethyltin (MMT) is the only methylation product of the tin(II) reacting with MeI observed. At the 95% confidence level, the pH, MeI and S are significant for the MMT yield. The concentration of MMT in the reactor increases with increase in pH within the selected pH range of 4,9 because four different species of Sn(II),Sn2+, SnOH+, Sn(OH)20 and Sn(OH)3,,have different reaction activities with MeI. The methylation activity of Sn(II) was found to be highest at a salinity of 0.1 M at three different pH levels: 5, 7 and 9. Higher concentration of Cl, (as a relatively weak nucleophilic ion) will obstruct nucleophilic attack of Sn(II) on MeI. MMT production also increases with rising volume of MeI. Moreover, first-order reaction rates have been calculated at different pH, salinity and MeI, and found to be in the range 0.0018,0.0199 h,1. The reaction rate also varies largely under different reaction conditions. One probable mechanism for the methylation reaction of Sn(II) with MeI is a SN2 nucleophilic attack on the methyl group of MeI by Sn(II), via a process of oxidative methyl-transfer. Copyright © 2006 John Wiley & Sons, Ltd. [source] Effect of disaccharides on the stabilization of bovine trypsin against detergent and autolysisBIOTECHNOLOGY PROGRESS, Issue 3 2010Shivcharan Prasad Abstract Osmolytes have been reported to stabilize biomolecules and even whole organisms against exposure to adverse environmental conditions. In this work, we report for the first time the use of some of these osmolytes, viz., the disaccharides trehalose and sucrose, in the stabilization of bovine trypsin against exposure to the anionic detergent sodium dodecyl sulfate and autolysis. Exposure of trypsin to SDS at a molar ratio of 1:45 led to decrease in trypsin activity by 61%. In the presence of 1 M sucrose and 1 M trehalose, the residual trypsin activity was found to increase to that of original enzyme activity. These two disaccharides were also found to slow down the rate of autolysis, resulting in residual activities of 80 and 88%, respectively, after incubation for 24 h. Active site titration showed retention of the fraction of active sites in the presence of trehalose. Fluorescence and CD spectroscopies were used to decipher the probable mechanism of this protective role of the disaccharides. Although complete resumption of secondary structure was not seen in the presence of the two disaccharides, the spectra of trypsin in the presence of stabilizers resembled the spectrum of native trypsin and were significantly different from the spectrum of detergent-denatured enzyme. Correlating the data obtained from spectroscopy with those obtained from activity assay, we propose that the retention of secondary structure of the enzyme is largely responsible for the retention of the functionally active form of trypsin. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] Cobalt Hydroxide Nanosheets and Their Thermal Decomposition to Cobalt Oxide NanoringsCHEMISTRY - AN ASIAN JOURNAL, Issue 4 2008Xiaohe Liu Dr. Abstract We demonstrate herein that single-crystalline ,-cobalt hydroxide (,-Co(OH)2) nanosheets can be successfully synthesized in large quantities by a facile hydrothermal synthetic method with aqueous cobalt nitrate as the cobalt source and triethylamine as both an alkaline and a complexing reagent. This synthetic method has good prospects for the future large-scale production of single-crystalline ,-Co(OH)2 nanosheets owing to its high yield, low cost, and simple reaction apparatus. Single-crystalline porous nanosheets and nanorings of cobalt oxide (Co3O4) were obtained by a thermal-decomposition method with single-crystalline ,-Co(OH)2 nanosheets as the precursor. A probable mechanism of formation of ,-Co(OH)2 nanosheets, porous Co3O4 nanosheets, and Co3O4 nanorings was proposed on the basis of the experimental results. [source] Micellar catalysis on the redox reaction of glycolic acid with chromium(VI)INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 6 2001Kabir-ud-Din Chromium(VI) oxidation of glycolic acid in the absence and presence of cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPB) followed the same mechanism as shown by kinetic study. The reaction followed second-order kinetics, first-order in each reactant. The oxidation is strongly catalyzed by manganese(II) and cationic micelles of CTAB or CPB. The catalytic effect of micelles can be fitted to a model in which the reaction rate depends upon the concentration of both reactants in the micellar pseudophase. Some added inorganic salts (NaCl, NaBr, NaNO3, and Na2SO4) reduce the micellar catalysis by excluding glycolic acid from the reaction site. The reactivity of glycolic acid towards chromium(VI) has been discussed and also compared with those obtained previously for the reaction between chromium(VI) and the reductants oxalic and lactic acids. On the basis of the observed results, probable mechanisms have been proposed. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 377,386, 2001 [source] Effects and probable mechanisms of electroacupuncture at the Zusanli point on upper gastrointestinal motility in rabbitsJOURNAL OF GASTROENTEROLOGY AND HEPATOLOGY, Issue 10 2007Wei-Xin Niu Abstract Background and Aim:, The purposes of this study were to investigate the regulative effect of acupuncture on gastrointestinal motility in rabbits and to explore the probable mechanism of electroacupuncture. Methods:, The experiment was performed on 30 rabbits implanted with three pairs of electrodes, which were equally divided into three groups: the control group, the Zusanli group, and the non-acupuncture point group. The gastrointestinal myoelectrical activity of each conscious rabbit was recorded when acupuncture was applied. Motilin in plasma, cholecystokinin (CCK) in serum, the activity of acetylcholine esterase, nitric oxide synthase (NOS), and the vesicle of nerve endings in the stomach tissue and jejunum were investigated. Results:, It was found that electroacupuncture did not exert much influence on the slow wave of gastrointestinal myoelectrical activity, but significantly increased the number and amplitude of spikes. In the Zusanli group, the concentration of motilin and CCK was much higher at the post-acupuncture stage than at the pre-acupuncture stage. Electroacupuncture significantly enhanced the activity of acetylcholine esterase. Moreover, we found out that in the Zusanli group, the number of vesicles without granula was significantly fewer than in the control group. The activity of NOS was less in the Zusanli group than in the control group. Conclusions:, Acupuncture may enhance the gastrointestinal myoelectrical activity of conscious rabbits. The cholinergic nerve, nitric oxide, motilin, and CCK may contribute to acupuncture mechanisms. [source] Wound healing effects of noni (Morinda citrifolia L.) leaves: a mechanism involving its PDGF/A2A receptor ligand binding and promotion of wound closurePHYTOTHERAPY RESEARCH, Issue 10 2010Afa Palu Abstract Morinda citrifolia L. (Rubiaceae) commonly known as noni, has been used in Polynesia by traditional healers for the treatment of cuts, bruises and wounds. Our objective was to investigate the wound-healing mechanisms of the noni leaf. The investigations of its wound-healing mechanisms were carried out using fresh noni leaf juice (NLJ), noni leaf ethanol extract (NLEE) and its methanol (MFEE) and hexane (HFEE) fractions on the PDGF and A2A receptors in vitro and topically in mice. Fresh noni leaf juice showed significant affinity to PDGF receptors, and displayed 166% binding inhibition of the ligand binding to its receptors, while at the same concentration, it only had 7% inhibition of the ligand binding to the A2A receptors. NLEE, HFEE and MFEE showed significant affinity to A2A receptors, concentration dependently, with IC50 values of 34.1, 42.9 and 86.7,,g/mL, respectively. However, MFEE significantly increased wound closure and reduced the half closure time in mice with a CT50 of 5.4 ± 0.2 days compared with control (p < 0.05). These results suggest that noni leaf significantly accelerated wound healing in mice via its ligand binding to the PDGF and A2A receptors as its probable mechanisms of wound-healing and also support its traditional usage for wound-healing in Polynesia. Copyright © 2010 John Wiley & Sons, Ltd. [source] | ||||||||||||||||