Major Pathway (major + pathway)

Distribution by Scientific Domains
Distribution within Life Sciences

Selected Abstracts

Biosynthesis of cellulose-enriched tension wood in Populus: global analysis of transcripts and metabolites identifies biochemical and developmental regulators in secondary wall biosynthesis

Sara Andersson-Gunnerås
Summary Stems and branches of angiosperm trees form tension wood (TW) when exposed to a gravitational stimulus. One of the main characteristics of TW, which distinguishes it from normal wood, is the formation of fibers with a thick inner gelatinous cell wall layer mainly composed of crystalline cellulose. Hence TW is enriched in cellulose, and deficient in lignin and hemicelluloses. An expressed sequence tag library made from TW-forming tissues in Populus tremula (L.) × tremuloides (Michx.) and data from transcript profiling using microarray and metabolite analysis were obtained during TW formation in Populus tremula (L.) in two growing seasons. The data were examined with the aim of identifying the genes responsible for the change in carbon (C) flow into various cell wall components, and the mechanisms important for the formation of the gelatinous cell wall layer (G-layer). A specific effort was made to identify carbohydrate-active enzymes with a putative function in cell wall biosynthesis. An increased C flux to cellulose was suggested by a higher abundance of sucrose synthase transcripts. However, genes related to the cellulose biosynthetic machinery were not generally affected, although the expression of secondary wall-specific CesA genes was modified in both directions. Other pathways for which the data suggested increased activity included lipid and glucosamine biosynthesis and the pectin degradation machinery. In addition, transcripts encoding fasciclin-like arabinogalactan proteins were particularly increased and found to lack true Arabidopsis orthologs. Major pathways for which the transcriptome and metabolome analysis suggested decreased activity were the pathway for C flux through guanosine 5,-diphosphate (GDP) sugars to mannans, the pentose phosphate pathway, lignin biosynthesis, and biosynthesis of cell wall matrix carbohydrates. Several differentially expressed auxin- and ethylene-related genes and transcription factors were also identified. [source]

Synergistic genotoxicity caused by low concentration of titanium dioxide nanoparticles and p,p,-DDT in human hepatocytes

Yun Shi
Abstract The use of titanium dioxide nanoparticles (nano-TiO2) for the degradation of dichlorodiphenyltrichloroethane (p,p,-DDT) increases the risk of exposure to trace nano-TiO2 and p,p,-DDT mixtures. The interaction of p,p,-DDT and nano-TiO2 at low concentrations may alter toxic response relative to nano-TiO2 or p,p,-DDT alone. In this work, the combined genotoxicity of trace nano-TiO2 and p,p,-DDT on human embryo L-02 hepatocytes without photoactivation was studied. Nano-TiO2 (0.1 g/L) was mixed with 0.01,1 mmol/L p,p,-DDT to determine adsorption isotherms. L-02 cells were exposed to different levels of p,p,-DDT (0, 0.001, 0.01, and 0.1 ,mol/L) and nano-TiO2 (0, 0.01, 0.1, and 1 ,g/mL) respectively. The adsorption of p,p,-DDT by nano-TiO2 was approximately 0.3 mmol/g. Cell viability, apoptosis, and DNA double strand breaks were similar among all test groups. Nano-TiO2 alone (0.01,1 ,g/mL) increased the levels of oxidative stress and oxidative DNA adducts (8-OHdG), but it did not induce DNA breaks or chromosome damage. Addition of trace nano-TiO2 with trace p,p,-DDT synergistically enhanced genotoxicity via increasing oxidative stress, oxidative DNA adducts, DNA breaks, and chromosome damage in L-02 cells. Low concentrations of nano-TiO2 and p,p,-DDT increased oxidativestress by reactive oxygen species (ROS) formation and lipid oxidation. Oxidative stress is a major pathway for DNA and chromosome damage. Dose-dependent synergistic genotoxicity induced by combined exposure of trace p,p,-DDT and nano-TiO2 suggests a potential environmental risk of nano-TiO2 assisted photocatalysis. Environ. Mol. Mutagen., 2010. © 2009 Wiley-Liss, Inc. [source]

Variations of chemical compositions in coarse aerosols and fine aerosols in two successive episodes

Chung-Yih Kuo
Abstract Particulate matter with diameters less than 2.5 ,m (PM2.5) and ranging between 10 to 2.5 ,m (PM10-2.5) were simultaneously collected at four air-quality monitoring stations in the Taichung area of central Taiwan during the period of February 12 to 22, 2004. Two different types of PM10 episodes, a nonlocal dust-storm episode and a local episode, were observed in the present study. High concentrations of coarse aerosols occurred during the dust-storm episode, whereas high concentrations of fine aerosols were present during the local episode. Relatively high levels of Na+, Mg2+, Ca2+, and Cl, in coarse aerosols were observed during the dust-storm episode. Very high concentrations of secondary aerosols (NH+4, SO2,4, and NO,3) in fine aerosols were observed during the local episode. The nitrate ion demonstrated the greatest increase in the ratios of ionic species to PM2.5 and ionic species to PM10-2.5 during the local episode. Significantly high ratios (0.444) of NO,3 to NO2 in fine aerosols were present during the local episode, indicating that the relatively high formation rate of NO,3 was one of the important factors leading to the increase of the NO,3 to PM2.5 ratio during the local episode. Results also showed that an abundant quantity of fine ammonium nitrate was formed during the local episode, and chloride depletion probably was the major pathway to form coarse NaNO3 during this episode. [source]

Kinetic and Equilibrium Studies of Reactions of N-Heterocycles with Dimeric and Monomeric Oxorhenium(V) Complexes

James H. Espenson
Abstract Equilibrium constants have been evaluated for the reaction {MeReO(edt)}2 + 2 L , 2 MeReO(edt)L, where edt is 1,2-ethanedithiolate and L is any of 13 N-donor heterocyclic ligands. The values of K range from 1.37(27)×10,2 for pyrimidine to 1.95(6)×106 for imidazole at 25 °C in chloroform. A successful correlation of logK with log (Ka) of HL+ was realized except in the case of the 2-substituted ligands 2-picoline and quinoline, where steric effects make K smaller than expected from the proton basicity of L. The kinetics of the same reactions were studied; the rate law for the reaction in the forward direction is given by ,d[{MeReO(edt)}2]/dt = {ka + kb[L]}[L] × [{MeReO(edt)}2]. Except for 2-picoline and quinoline, the major pathway is provided by the term that shows the quadratic dependence on [L]. Values of log (kb) also correlate with log K, and therefore necessarily with log (Ka). [source]

The ubiquitin-proteasome system and its role in ethanol-induced disorders

Terrence M. Donohue Jr
The levels of these proteins are controlled by their rates of degradation. Similarly, protein catabolism plays a crucial role in prolonging cellular life by destroying damaged proteins that are potentially cytotoxic. A major player in these catabolic reactions is the ubiquitin-proteasome system, a novel proteolytic system that has become the primary proteolytic pathway in eukaryotic cells. Ubiquitin-mediated proteolysis is now regarded as the major pathway by which most intracellular proteins are destroyed. Equally important, from a toxicological standpoint, is that the ubiquitin-proteasome system is also widely considered to be a cellular defense mechanism, since it is involved in the removal of damaged proteins generated by adduct formation and oxidative stress. This review describes the history and the components of the ubiquitin-proteasome system, its regulation and its role in pathological states, with the major emphasis on ethanol-induced organ injury. The available literature cited here deals mainly with the effects of ethanol consumption on the ubiquitin-proteasome pathway in the liver. However, since this proteolytic system is an essential pathway in all cells it is an attractive experimental model and therapeutic target in extrahepatic organs such as the brain and heart that are also affected by excessive alcohol consumption. [source]

Effect of monovalent cations and G-quadruplex structures on the outcome of intramolecular homologous recombination

FEBS JOURNAL, Issue 11 2009
Paula Barros
Homologous recombination is a very important cellular process, as it provides a major pathway for the repair of DNA double-strand breaks. This complex process is affected by many factors within cells. Here, we have studied the effect of monovalent cations (K+, Na+, and NH4+) on the outcome of recombination events, as their presence affects the biochemical activities of the proteins involved in recombination as well as the structure of DNA. For this purpose, we used an in vitro recombination system that includes a protein nuclear extract, as a source of recombination machinery, and two plasmids as substrates for intramolecular homologous recombination, each with two copies of different alleles of the human minisatellite MsH43. We found that the presence of monovalent cations induced a decrease in the recombination frequency, accompanied by an increase in the fidelity of the recombination. Moreover, there is an emerging consensus that secondary structures of DNA have the potential to induce genomic instability. Therefore, we analyzed the effect of the sequences capable of forming G-quadruplex on the production of recombinant molecules, taking advantage of the capacity of some MsH43 alleles to generate these kinds of structure in the presence of K+. We observed that the MsH43 recombinants containing duplications, generated in the presence of K+, did not include the repeats located towards the 5,-side of the G-quadruplex motif, suggesting that this structure may be involved in the recombination events leading to duplications. Our results provide new insights into the molecular mechanisms underlying the recombination of repetitive sequences. [source]

Characterization of a novel silkworm (Bombyx mori) phenol UDP-glucosyltransferase

FEBS JOURNAL, Issue 3 2002
Teresa Luque
Sugar conjugation is a major pathway for the inactivation and excretion of both endogenous and exogenous compounds. We report here the molecular cloning and functional characterization of a phenol UDP-glucosyltransferase (UGT) from the silkworm, Bombyx mori, which was named BmUGT1. The complete cDNA clone is 1.6 kb, and the gene is expressed in several tissues of fifth-instar larvae, including fat body, midgut, integument, testis, silk gland and haemocytes. The predicted protein comprises 520 amino acids and has ,,30% overall amino-acid identity with other members of the UGT family. The most conserved region of the protein is the C-terminal half, which has been implicated in binding the UDP-sugar. BmUGT1 was expressed in insect cells using the baculovirus expression system, and a range of compounds belonging to diverse chemical groups were assessed as potential substrates for the enzyme. The expressed enzyme had a wide substrate specificity, showing activity with flavonoids, coumarins, terpenoids and simple phenols. These results support a role for the enzyme in detoxication processes, such as minimizing the harmful effects of ingested plant allelochemicals. This work represents the first instance where an insect ugt gene has been associated with a specific enzyme activity. [source]

DNA base repair , recognition and initiation of catalysis

Bjørn Dalhus
Abstract Endogenous DNA damage induced by hydrolysis, reactive oxygen species and alkylation modifies DNA bases and the structure of the DNA duplex. Numerous mechanisms have evolved to protect cells from these deleterious effects. Base excision repair is the major pathway for removing base lesions. However, several mechanisms of direct base damage reversal, involving enzymes such as transferases, photolyases and oxidative demethylases, are specialized to remove certain types of photoproducts and alkylated bases. Mismatch excision repair corrects for misincorporation of bases by replicative DNA polymerases. The determination of the 3D structure and visualization of DNA repair proteins and their interactions with damaged DNA have considerably aided our understanding of the molecular basis for DNA base lesion repair and genome stability. Here, we review the structural biochemistry of base lesion recognition and initiation of one-step direct reversal (DR) of damage as well as the multistep pathways of base excision repair (BER), nucleotide incision repair (NIR) and mismatch repair (MMR). [source]

Interspecific carbon exchange and cost of interactions between basidiomycete mycelia in soil and wood

J. M. Wells
Summary 1.,The outcome of interactions between wood decay basidiomycete fungi is affected by the size of territory held by a mycelium. We investigated the outcomes of interactions between the cord-forming saprotrophs Phanerochaete velutina (DC: Pers.) Parm., Phallus impudicus (L.) Pers. and Hypholoma fasciculare (Huds: Fr) Kumner over 152,155 days, determined as ability to capture or share territory in soil and wood, in terms of decay partitioning and the carbon cost of interactions. 2.,The outcome of interactions in wood alone differed from those in which the fungi competed for an opponents' inoculum in soil microcosms. Competitive ability (the ability to capture or co-occupy an opponent's inoculum) varied according to species and inoculum age. In wood block pairings in the absence of soil there was evidence that P. velutina opportunistically utilized C previously mobilized within an opponent's inoculum. 3.,In soil systems, short-term (28-day) respiratory losses of preloaded 14C (supplied as glucose) indicated that interaction could have a substantial C cost, depending on the resource quality of the opponents' inocula. Phallus impudicus inocula accumulated 14C from opponents' mycelia during ,deadlock' interactions, although reciprocal interspecific 14C transfer was not observed. 4.,Saprotrophic cord-forming basidiomycetes are considered to be highly conservative of acquired nutrients, representing a significant nutrient reservoir in woodland ecosytems. Here we demonstrate that a potential major pathway for nutrient mineralization by this group is nutrient loss during competitive interactions in soil. [source]

Requirement of Runx1/AML1/PEBP2,B for the generation of haematopoietic cells from endothelial cells

GENES TO CELLS, Issue 1 2001
Tomomasa Yokomizo
Recent studies revealing that endothelial cells derived from E8.5-E10.5 mouse embryos give rise to haematopoietic cells appear to correspond to previous histological observations that haematopoietic cell clusters are attached to the ventral aspect of dorsal aorta in such a way as if they were budding from the endothelial cell layer. Gene disruption studies have revealed that Runx1/AML1 is required for definitive haematopoiesis but not for primitive haematopoiesis, but the precise stage of gene function is not yet known. We found that mice deficient in Runx1/AML1 (an , subunit of the transcription factor PEBP2/CBF) lack c-Kit+ haematopoietic cell clusters in the dorsal aorta, omphalomesenteric and umbilical arteries, as well as yolk sac vessels. Moreover, endothelial cells sorted from the embryo proper and the yolk sac of AML1,/, embryos are unable to differentiate into haematopoietic cells on OP9 stromal cells, whereas colonies of AML1,/, endothelial cells can be formed in culture. These results strongly suggest that the emergence of haematopoietic cells from endothelial cells represents a major pathway of definitive haematopoiesis and is an event that also occurs in the yolk sac in vivo, as suggested by earlier in vitro experiments. [source]

Novel EGF pathway regulators modulate C. elegans healthspan and lifespan via EGF receptor, PLC-,, and IP3R activation

AGING CELL, Issue 4 2010
Hiroaki Iwasa
Summary Improving health of the rapidly growing aging population is a critical medical, social, and economic goal. Identification of genes that modulate healthspan, the period of mid-life vigor that precedes significant functional decline, will be an essential part of the effort to design anti-aging therapies. Because locomotory decline in humans is a major contributor to frailty and loss of independence and because slowing of movement is a conserved feature of aging across phyla, we screened for genetic interventions that extend locomotory healthspan of Caenorhabditis elegans. From a group of 54 genes previously noted to encode secreted proteins similar in sequence to extracellular domains of insulin receptor, we identified two genes for which RNAi knockdown delayed age-associated locomotory decline, conferring a high performance in advanced age phenotype (Hpa). Unexpectedly, we found that hpa-1 and hpa-2 act through the EGF pathway, rather than the insulin signaling pathway, to control systemic healthspan benefits without detectable developmental consequences. Further analysis revealed a potent role of EGF signaling, acting via downstream phospholipase C-,plc-3 and inositol-3-phosphate receptor itr-1, to promote healthy aging associated with low lipofuscin levels, enhanced physical performance, and extended lifespan. This study identifies HPA-1 and HPA-2 as novel negative regulators of EGF signaling and constitutes the first report of EGF signaling as a major pathway for healthy aging. Our data raise the possibility that EGF family members should be investigated for similar activities in higher organisms. [source]

The norepinephrine transporter and its regulation

Prashant Mandela
Abstract For many years, the norepinephrine transporter (NET) was considered a ,static' protein that contributed to the termination of the action of norepinephrine in the synapse of noradrenergic neurons. The concept that the NET is dynamically regulated, adjusting noradrenergic transmission by changing its function and/or expression, was considered initially in the mid 1980s. Since that time, a plethora of studies demonstrate that the NET is regulated by several intracellular and extracellular signaling molecules, and that phosphorylation of the NET is a major pathway regulating its cell surface expression and thereby its function. The NET is a target of action of a number of drugs that are used long-term therapeutically or abused chronically. This has driven numerous investigations of how the NET and its function are regulated by long-term exposure to drugs. While repeated exposure to many drugs has been shown to affect NET function and expression, the intracellular mechanisms for these effects remains elusive. [source]

Canopy leaching of cations in Central European forest ecosystems , a regional assessment

Jens-Johann Langusch
Abstract The leaching of Ca, Mg, and K from canopies is a major pathway of these cations into forest soils. Our aim was to quantify rates of canopy leaching and to identify driving factors at the regional scale using annual fluxes of bulk precipitation and throughfall from 37 coniferous and deciduous forests of North and Central Europe. Total deposition of Ca, Mg, K, and H+ was estimated with Na as an index cation. The median canopy leaching increased in the order: Mg (0.11 kmolc ha,1 a,1) < Ca (0.31 kmolc ha,1 a,1) < K (0.39 kmolc ha,1 a,1). Canopy leaching of Ca and K was positively correlated with the calculated total H+ deposition and H+ buffered in the canopy, whereas canopy leaching of Mg was not. With contrasting effects, fluxes of SO4 -S and NH4 -N in throughfall explained to 64,% (P<0.001) of the Ca canopy leaching. Fluxes of NH4 -N and Ca were negatively correlated, suggesting that buffering of H+ by NH3 deposition reduced canopy leaching of Ca. Amount of bulk precipitation and SO4 -S in throughfall were identified as much weaker driving factors for canopy leaching of K (r2=0.28, P<0.01). Our results show that Ca is the dominant cation in buffering the H+ input in the canopy. At the regional and annual scale, canopy leaching of Mg appears to be unaffected by H+ deposition and H+ buffering in the canopy. Kronenauswaschung von Ca, Mg und K in mitteleuropäischen Waldökosystemen Die Kronenauswaschung von Ca, Mg und K mit dem Bestandesniederschlag stellt einen wichtigen Eintrag für die Waldböden dar. Ziel dieser Arbeit war es, die Kronenauswaschung dieser Kationen auf der regionalen Skala zu quantifizieren und Faktoren zu identifizieren, welche die Kronenauswaschung beeinflussen. Hierzu wurden annuelle Flüsse aus Freiland- und Bestandesniederschlägen von 37 nord- und mitteleuropäischen Laub- und Nadelwäldern ausgewertet. Zur Bestimmung der Gesamtdeposition wurde Na als Leitelement benutzt. Der Median der Kronenauswaschung stieg in der Reihenfolge Mg (0,11 kmolc ha,1 a,1) < Ca (0,31 kmolc ha,1 a,1) < K (0,39 kmolc ha,1 a,1) an. Die Kronenauswaschung von Ca und K war positiv mit der berechneten H+ -Deposition und der gepufferten H+ -Menge im Kronenraum korreliert, während Mg keinen Zusammenhang zeigte. Die Kronenauswaschung von Ca ließ sich zu 64,% (P<0.001) mit den Flüssen von SO4 -S und NH4 -N im Bestandesniederschlag erklären, wobei die negative Korrelation zwischen NH4 -N und Ca auf eine Reduzierung der Ca-Kronenauswaschung mit steigender NH3 -Deposition hindeutet. Dagegen konnten nur 28,% der K-Auswaschung (P<0.01) mit dem Freilandniederschlag und dem SO4 -S-Fluss im Bestandesniederschlag als Indikatorvariablen erklärt werden. Unsere Studie zeigt, dass Calcium das dominante Kation bei der Kronenraumpufferung von H+ ist. Auf der regionalen und annuellen Skala scheint die Kronenauswaschung von Mg weder von der H+ -Deposition noch von der Menge im Kronenraum gepufferter H+ -Ionen abzuhängen. [source]

Characterization of urinary metabolites of testosterone, methyltestosterone, mibolerone and boldenone in greyhound dogs

T. M. Williams
Androgenic steroids are used in female greyhound dogs to prevent the onset of estrus; moreover, these steroids also have potent anabolic activity. As anabolic steroids increase muscle mass and aggression in animals, the excessive use of these agents in racing greyhounds gives an unfair performance advantage to treated dogs. The biotransformation of most anabolic steroids has not been determined in greyhound dogs. The objective of the present study was to identify the urinary metabolites of testosterone, methyltestosterone, mibolerone, and boldenone in greyhound dogs. These steroids were administered orally (1 mg/kg) to either male or female greyhound dogs and urine samples were collected pre-administration and at 2, 4, 8, 12, 24, 72, and 96 h post-administration. Urine extracts were analyzed by high-performance liquid chromatography/mass spectrometry (HPLC/MS) to identify major metabolites and to determine their urinary excretion profiles. Major urinary metabolites, primarily glucuronide, conjugated and free, were detected for the selected steroids. Sulfate conjugation did not appear to be a major pathway for steroid metabolism and excretion in the greyhound dog. Phase I biotransformation was also evaluated using greyhound dog liver microsomes from untreated dogs. The identification of several in vivo steroid metabolites generated in this study will be useful in detecting these steroids in urine samples submitted for drug screening. [source]

Mass spectrometry of the photolysis of sulfonylurea herbicides in prairie waters

John V. Headley
Abstract This review of mass spectrometry of sulfonylurea herbicides includes a focus on studies relevant to Canadian Prairie waters. Emphasis is given to data gaps in the literature for the rates of photolysis of selected sulfonylurea herbicides in different water matrices. Specifically, results are evaluated for positive ion electrospray tandem mass spectrometry with liquid chromatography separation for the study of the photolysis of chlorsulfuron, tribenuron-methyl, thifensulfuron-methyl, metsulfuron-methyl, and ethametsulfuron-methyl. LC,MS/MS is shown to be the method of choice for the quantification of sulfonylurea herbicides with instrumental detection limits ranging from 1.3 to 7.2,pg (on-column). Tandem mass spectrometry coupled with the use of authentic standards likewise has proven to be well suited for the identification of transformation products. To date, however, the power of time-of-flight MS and ultrahigh resolution MS has not been exploited fully for the identification of unknown photolysis products. Dissipation of the herbicides under natural sunlight fit pseudo-first-order kinetics with half-life values ranging from 4.4 to 99 days. For simulated sunlight, radiation wavelengths shorter than 400,nm are required to induce significant photolytic reactions. The correlation between field dissipation studies and laboratory photolysis experiments suggests that photolysis is a major pathway for the dissipation of some sulfonylurea herbicides in natural Prairie waters. © 2009 Wiley Periodicals, Inc., Mass Spec Rev 29:593,605, 2010 [source]

A peroxide-induced zinc uptake system plays an important role in protection against oxidative stress in Bacillus subtilis

Ahmed Gaballa
Summary In Bacillus subtilis, hydrogen peroxide (H2O2) induces expression of the PerR regulon including catalase (KatA), alkyl hydroperoxide reductase and the DNA-binding protein MrgA. We have identified the P-type metal-transporting ATPase ZosA (formerly YkvW) as an additional member of the perR regulon. Expression of zosA is induced by H2O2 and repressed by the PerR metalloregulatory protein, which binds to two Per boxes in the promoter region. Physiological studies implicate ZosA in Zn(II) uptake. ZosA functions together with two Zur-regulated uptake systems and one known efflux system to maintain Zn(II) homeostasis. ZosA is the major pathway for zinc uptake in cells growing with micromolar levels of Zn(II) that are known to repress the two Zur-regulated transporters. A perR mutant is sensitive to high levels of zinc, and this sensitivity is partially suppressed by a zosA mutation. ZosA is important for resistance to both H2O2 and the thiol-oxidizing agent diamide. This suggests that increased intracellular Zn(II) may protect thiols from oxidation. In contrast, catalase is critical for H2O2 resistance but does not contribute significantly to diamide resistance. Growth of cells with elevated zinc significantly increases resistance to high concentrations of H2O2, and this effect requires ZosA. Our results indicate that peroxide stress leads to the upregulation of a dedicated Zn(II) uptake system that plays an important role in H2O2 and disulphide stress resistance. [source]

Xylem sap flow as a major pathway for oxygen supply to the sapwood of birch (Betula pubescens Ehr.)

ABSTRACT The role of xylem sap flow as an aqueous pathway for oxygen supply to the wood parenchyma of Betula pubescens saplings was investigated. Using micro-optode sensors the oxygen status of the sapwood was quantified in relation to mass flow of xylem sap. Sap flow was gradually reduced by an increasing oxygen depletion in the root space. The effect of sap flow on radial O2 transport between stem and atmosphere was assessed by a stoichiometrical approach between respiratory CO2 production and O2 consumption. Restriction of sap flow set in 36.5 h after the onset of O2 depletion, and was complete after 71 h. Interruption of sap flow drastically increased the O2 deficit in the sapwood to 70%. Sap flow contributed about 60% to the total oxygen supply to the sapwood. Diurnal O2 flow rates varied between 3 and 6.3 nmol O2 m,2 leaf area (LA) s,1 during night- and daytime, respectively. Maximum O2 flow rates of 20 nmol O2 m,2 LA s,1 were reached at highest sap flow rates of 5.7 mmol H2O m,2 LA s,1. Sap flow not only affected the oxygen status of the sapwood but also had an effect on radial O2 transport between stem and atmosphere. [source]

In vitro metabolism of , -lapachone (ARQ 501) in mammalian hepatocytes and cultured human cells

Xiu-Sheng Miao
ARQ 501 (3,4-dihydro-2,2-dimethyl-2H -naphthol[1,2-b]pyran-5,6-dione, , -lapachone) is an anticancer agent, currently in multiple phase II clinical trials as monotherapy and in combination with other cytotoxic drugs. This study focuses on in vitro metabolism in cryopreserved hepatocytes from mice, rats, dogs and humans using [14C]-labeled ARQ 501. Metabolite profiles were characterized using liquid chromatography/mass spectrometry combined with an accurate radioactivity counter. Ion trap mass spectrometry was employed for further structural elucidation. A total of twelve metabolites were detected in the mammalian hepatocytes studied; all of which but one were generated from phase II conjugation reactions. Ten of the observed metabolites were produced by conjugations occurring at the reduced ortho -quinone carbonyl groups of ARQ 501. The metabolite profiles revealed that glucuronidation was the major biotransformation pathway in mouse and human hepatocytes. Monosulfation was the major pathway in dog, while, in rat, it appears glucuronidation and sulfation pathways contributed equally. Three major metabolites were found in rats: monoglucuronide M1, monosulfate M6, and glucuronide-sulfate M9. Two types of diconjugation metabolites were formed by attachment of the second glycone to an adjacent hydroxyl or to an existing glycone. Of the diconjugation metabolites, glucosylsulfate M10, diglucuronide M5, and glucuronide-glucoside M11 represent rarely observed phase II metabolites in mammals. The only unconjugated metabolite was generated through hydrolysis and was observed in rat, dog and human hepatocytes. ARQ 501 appeared less stable in human hepatocytes than in those of other species. To further elucidate the metabolism of ARQ 501 in extrahepatic sites, its metabolism in human kidney, lung and intestine cells was also studied, and only monoglucuronide M1 was observed in all the cell types examined. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Lateralization During the Weber Test: Animal Experiments

Jean-Yves Sichel MD
Abstract Objectives/Hypothesis The objective of this study were to present an assessment of a new theory to explain lateralization during the Weber test using an animal model. This theory is based on the discovery that a major pathway in bone conduction stimulation to the inner ear is through the skull contents (probably the cerebrospinal fluid [CSF]). The placement of a bone vibrator or tuning fork on the skull excites the inner ear by the classic osseous pathway and by the suggested CSF pathway. We assume that there is a phase difference between the stimulation mediated by the ossicular chain (inertial and occlusion mechanisms) and the one mediated by the CSF. The presence of a conductive pathology will decrease the magnitude of the sound energy mediated by the ossicular chain. Thus, the out-of-phase signal arriving through the bony pathways will be decreased, hence increasing the resultant sound intensity stimulating the cochlea. Study Design Prospective animal study. Methods The experiment was performed on 10 fat sand rats, which had undergone unilateral cochleostomy and a small craniotomy. The auditory nerve brainstem response (ABR) thresholds were measured to air-conducted stimulation, to stimulation with the bone vibrator applied to the skull, and to stimulation with the bone vibrator applied directly to the brain through the craniotomy. The ossicular chain of the second ear was then fixed to the middle ear walls with cyanoacrylate glue to induce a conductive hearing loss. The ABR thresholds to the same three stimuli were then measured again. Results After ossicular chain fixation, the ABR threshold to air-conducted stimulation increased, to bone vibrator stimulation on the bone decreased (hearing improvement), and to bone vibrator stimulation directly on the brain remained unchanged. Conclusions This experiment confirms the proposed theory. During clinical bone conduction stimulation, there is a phase difference between sound energy reaching the inner ear through the middle ear ossicles and from the CSF. A middle ear conductive pathology removes one of these components, thus increasing the effective sound intensity in the affected ear. On the other hand, when the bone vibrator is applied on the brain, the inner ear is stimulated only through the CSF, so ossicular chain fixation does not change the ABR threshold. Moreover, this study proves that lateralization during the Weber phenomenon is the result, at least in part, of an intensity difference between sound energy reaching the two cochleae. [source]

New insights into plant transaldolase

Maxime Caillau
Summary The oxidative pentose phosphate pathway (OPPP) provides plants with important substrates for both primary and secondary metabolism via the oxidation of glucose-6-phosphate. The OPPP is also thought to generate large amounts of reducing power to drive various anabolic processes. In animals this major pathway is located within the cytoplasm of cells, but in plants its subcellular compartmentation is far from clear. Although several enzymes of the OPPP were demonstrated to have both cytosolic and plastidic counterparts, there is yet no evidence for a full set of functional enzymes in each compartment. We report here the isolation of two coding sequences from tomato (Lycopersicon esculentum L.) which encode phylogenetically distant sequences (ToTal1 and ToTal2) that putatively encode distinct plastidic TA isoforms. The kinetic characterization of ToTal1 revealed that, unlike other enzymes of the non-oxidative branch of the OPPP, ToTal1 does not follow a Michaelis,Menten mode of catalysis which has implications for its role in regulating carbon flux between primary and secondary metabolism. TA genes appear to be differentially regulated at the level of gene expression in plant tissues and in response to environmental factors which suggests that TA isoforms have a non-overlapping role for plant metabolism. [source]

Anti-thrombin Therapy During Warm Ischemia and Cold Preservation Prevents Chronic Kidney Graft Fibrosis in a DCD Model

F. Favreau
Ischemia reperfusion injury (IRI) is pivotal for renal fibrosis development via peritubular capillaries injury. Coagulation represents a key mechanism involved in this process. Melagatran® (M), a thrombin inhibitor, was evaluated in an autotransplanted kidney model, using Large White pigs. To mimic deceased after cardiac death donor conditions, kidneys underwent warm ischemia (WI) for 60 min before cold preservation for 24 h in University of Wisconsin solution. Treatment with M before WI and/or in the preservation solution drastically improved survival at 3 months, reduced renal dysfunction related to a critical reduction in interstitial fibrosis, measured by Sirius Red staining. Tissue analysis revealed reduced expression of transforming growth factor-, (TGF-,) and activation level of its effectors phospho-Smad3, Smad4 and connective tissue growth factor (CTGF) after M treatment. Fibrinolysis activation was also observed, evidenced by downregulation of PAI-1 protein and gene expression. In addition, M reduced S100A4 expression and vimentin staining, which are markers for epithelial mesenchymal transition, a major pathway to chronic kidney fibrosis. Finally, expression of oxidative stress markers Nox2 and iNOS was reduced. We conclude that inhibition of thrombin is an effective therapy against IRI that reduces chronic graft fibrosis, with a significantly positive effect on survival. [source]

Pathogenesis of equine herpesvirus-1 infection in the mouse model

APMIS, Issue 1 2009
Equine herpesvirus-1 (EHV-1) is a major equine pathogen causing respiratory diseases, abortions and severe neurological disorders. The basis of neurological disturbances is, as in other organs, infection of endothelial cells, followed by vasculitis, thrombosis and ischaemic damage of the parenchyma. Here, a murine model was used to explore the mechanism of entry to, and spread within the brain, the cell affinity of the agent and the modulating role of the immune defence, which are all factors governing the pathogenesis of the neurological disease. Because controversial views exist about these mechanisms, we undertook a neuropathological study with intranasally infected adult mice. EHV-1 entered the brain through the olfactory neuroepithelium and along the olfactory nerves, and spread transsynaptically in rostro-caudal direction, using olfactory and limbic neuronal networks. Exclusively neurons were infected. The cellular immune reaction exerted a restraining effect on virus dissemination. Following nasal infection, the olfactory route was the major pathway for virus entry and dissemination, involvement of the trigeminal nerve in virus spread seems much less probable. In the adult mouse brain EHV-1 behaves as a typical neurotropic agent, using, similarly to other herpesviruses, the neuronal networks for dissemination. Vasculitis, the predominant type of lesion in natural infection, and endothelial cell positivity for EHV-1 were detectable only in the lung. Thus, this agent exhibits in the mouse a dual affinity: it is neurotropic in the brain, and endotheliotropic in visceral organs. Consideration of pathogenetic aspects of equine and experimental murine EHV-1 infections also helps a better understanding of human herpetic brain disease. [source]

Fish movements: the introduction pathway for topmouth gudgeon Pseudorasbora parva and other non-native fishes in the UK

G. H. Copp
Abstract 1.The contamination of fish consignments (for stocking or aquaculture) is a major pathway by which non-native organisms, including fish, are introduced to new areas. One of the best examples of this is the topmouth gudgeon Pseudorasbora parva, which was accidentally imported into Romania and then throughout Europe in consignments of Asian carp species. 2.The introduction and spread of topmouth gudgeon in the UK has been linked to imports and movements of the ornamental variety (golden orfe) of ide Leuciscus idus. To examine this hypothesis, relationships between authorized movements of both native and non-native fish species (in particular ide) and the occurrence in England of topmouth gudgeon were tested at the 10×10,km scale. 3.Topmouth gudgeon occurrence in the wild was significantly correlated with the trajectories of movements of ornamental fish species (ide/orfe, sunbleak Leucaspius delineatus) as well as a few non-ornamental fish species (European catfish Silurus glanis, Atlantic salmon Salmo salar and grass carp Ctenopharyngodon idella). 4.These results highlight the mechanism by which non-native fish species disperse from the point of first introduction, and especially that movements of fish within the country represent an important mechanism for accidental introductions of non-native species. © Crown copyright 2010. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd. [source]

Pharmacokinetics of TDP223206 following intravenous and oral administration to intact rats and intravenous administration to bile duct-cannulated rats

Yanmin Chen
Abstract The pharmacokinetics of TDP223206 was studied following single intravenous and oral administrations in rats. A mixture of TDP223206 and 14C-TDP223206 were administered to intact and bile duct-cannulated rats. Following intravenous administration, plasma concentrations declined biphasically. The AUCinf increased linearly with dose but was not dose proportional. The PK parameters of TDP223206 indicated low clearance (254,386,ml/h/kg) and a moderate volume of distribution (968,1883,ml/kg). The bioavailability was 32.95% and 24.46% for 10 and 50,mg/kg oral doses, respectively. 14C-TDP223206 was distributed widely into different tissues with small intestine, liver, kidneys and large intestine having large tissue to plasma ratios. 14C-TDP223206 was the major circulating component in the plasma. A total of 91.2% of administered radioactivity of 14C-TDP223206 was recovered in bile indicating that biliary excretion was the major pathway for drug elimination. 14C-TDP223206-acyl glucuronides were the major metabolites in bile. The oxo- 14C-TDP223206 was the major metabolite in plasma and an important metabolite in bile. Two forms of diastereomeric acyl glucuronides of 14C-TDP223206 were detected in bile with similar LC/MS intensities suggesting a similar biotransformation capacity. Only one form of these 14C-TDP223206-acyl glucuronides was detected in plasma suggesting that enterohepatic recirculation was related to the nature of the stereo-isomers. Copyright © 2008 John Wiley & Sons, Ltd. [source]

A Time-Resolved Spectroscopic Study of the Bichromophoric Phototrigger 3,,5,-Dimethoxybenzoin Diethyl Phosphate: Interaction Between the Two Chromophores Determines the Reaction Pathway

Chensheng Ma Dr.
Abstract 3,,5,-Dimethoxybenzoin (DMB) is a bichromophoric system that has widespread application as a highly efficient photoremovable protecting group (PRPG) for the release of diverse functional groups. The photodeprotection of DMB phototriggers is remarkably clean, and is accompanied by the formation of a biologically benign cyclization product, 3,,5,-dimethoxybenzofuran (DMBF). The underlying mechanism of the DMB deprotection and cyclization has, however, until now remained unclear. Femtosecond transient absorption (fs-TA) spectroscopy and nanosecond time-resolved resonance Raman (ns-TR3) spectroscopy were employed to detect the transient species directly, and examine the dynamic transformations involved in the primary photoreactions for DMB diethyl phosphate (DMBDP) in acetonitrile (CH3CN). To assess the electronic character and the role played by the individual sub-chromophore, that is, the benzoyl, and the di- meta -methoxybenzylic moieties, for the DMBDP deprotection, comparative fs-TA measurements were also carried out for the reference compounds diethyl phosphate acetophenone (DPAP), and 3,,5,-dimethoxybenzylic diethyl phosphate (DMBnDP) in the same solvent. Comparison of the fs-TA spectra reveals that the photoexcited DMBDP exhibits distinctly different spectral character and dynamic evolution from those of the reference compounds. This fact, combined with the related steady-state spectral and density functional theoretical results, strongly suggests the presence in DMBDP of a significant interaction between the two sub-chromophores, and that this interaction plays a governing role in determining the nature of the photoexcitation and the reaction channel of the subsequent photophysical and photochemical transformations. The ns-TR3 results and their correlation with the fs-TA spectra and dynamics provide evidence for a novel concerted deprotection,cyclization mechanism for DMBDP in CH3CN. By monitoring the direct generation of the transient DMBF product, the cyclization time constant was determined unequivocally to be ,1,ns. This indicates that there is little relevance for the long-lived intermediates (>10,ns) in giving the DMBF product, and excludes the stepwise mechanism proposed in the literature as the major pathway for the DMB cyclization reaction. This work provides important new insights into the origin of the 3,,5,-dimethoxy substitution effect for the DMB photodeprotection. It also helps to clarify the many different views presented in previous mechanistic studies of the DMB PRPGs. In addition to this, our fs-TA results on the reference compound DMBnDP in CH3CN provide the first direct observation (to the best of our knowledge) showing the predominance of a prompt (,2,ps) heterolytic bond cleavage after photoexcitation of meta -methoxybenzylic compounds. This provides insight into the long-term controversies about the photoinitiated dissociation mode of related substituted benzylic compounds. [source]

Analysis Of Agonist-Evoked Nitric Oxide Release From Human Endothelial Cells: Role Of Superoxide Anion

Monique David-Dufilho
SUMMARY 1. Dichlorofluorescein oxidation and electrochemical monitoring of in situ nitric oxide (NO) release from cultured human endothelial cells reveals that agonists such as thrombin and histamine simultaneously stimulate transient superoxide production. 2. The duration of ·NO release was increased only in the simultaneous presence of extracellular L -arginine and exogenous superoxide dismutase. In contrast, the inhibition of membrane reduced nicotinamide adenine dinucleotide (phosphate) oxidases, the major source of ·O2, in endothelial cells, did not prolong ·NO release, although extracellular L -arginine was also present. Comparison of these two experimental conditions suggested that H2O2 was involved in the extension of the ·NO signal. 3. The present study demonstrates that, in the absence of external L -arginine, ·O2, production does not constitute the major pathway controlling the duration of agonist-induced ·NO signal. These results suggest that L -arginine and H2O2 act jointly to maintain nitric oxide synthase in an activated form. [source]

The contribution of hepatic steroid metabolism to serum estradiol and estriol concentrations in nonylphenol treated MMTVneu mice and its potential effects on breast cancer incidence and latency

Ricardo Acevedo
Abstract The two major pathways for the metabolism of estradiol-17, (E2) are the 2- and 16-hydroxylase pathways. Research has suggested that the increased production of the estrogenically active 16-hydroxy products such as estriol (E3) may be involved in increased susceptibility to breast cancer. 4-Nonylphenol (4-NP) is an environmental estrogen that also can activate the pregnane-X receptor (PXR) and induce P-450 enzymes responsible for the production of E3. It is hypothesized that 4-NP may act in part as an environmental estrogen by increasing E3 production. Based on its affinity for the estrogen receptor (ER) alone, 4-NP may be more potent than predicted at increasing mammary cancer incidence in the MMTVneu mouse. Female mice were treated per os for 7 days at 0, 25, 50 or 75 mg kg,1 day,1 4-NP to investigate the effects of 4-NP on hepatic estrogen metabolism after an acute treatment. 4-Nonylphenol increased the hepatic formation of E3 in a dose-dependent manner. However, serum E3 concentrations were only increased at 25 mg kg,1 day,1 presumably due to direct inhibition of E3 formation by 4-NP. MMTVneu mice were then treated for 32 weeks at 0, 30 or 45 mg kg,1 day,1 4-NP to determine its effects on mammary cancer formation and estrogen metabolism. 4-Nonylphenol increased mammary cancer formation in the MMTVneu mice at 45 mg kg,1 day,1 but not at 30 mg kg,1 day,1. Mice treated with an equipotent dose of E2, 10 µg kg,1 day,1, based on the relative binding affinities of nonylphenol and estradiol for ER,, did not develop mammary cancer. This suggests that nonylphenol is more potent than predicted based on its affinity for the estrogen receptor. However, no changes in serum E3 concentrations or hepatic E3 production were measured after the chronic treatment. Changes in E3 formation were correlated with increased CYP2B levels after the 7 day 4-NP treatment, and repression of CYP2B and CYP3A after 32 weeks of 4-NP treatment. Microarray analysis and Q-PCR of liver mRNA from the mice treated for 32 weeks demonstrated a decrease in RXR,, the heterodimeric partner of the PXR, which may in part explain the repressed transcription of the P450s measured. In conclusion, 4-NP treatment for 32 weeks increased mammary cancer formation at a dose of 45 mg kg,1 day,1. However, chronic treatment with 4-NP did not increase hepatic E3 formation or serum E3 concentrations. The transient induction by 4-NP of hepatic E3 formation and serum concentrations is most likely not involved in the increased incidence of mammary cancer in MMTVneu mice since E3 serum concentrations were only increased at 25 mg kg,1 day,1, a dose that was not sufficient to induce mammary tumor formation. Nevertheless, the induced hepatic E3 production in the acute exposures to 4-NP was indicative of an increase in mammary cancer incidence after the chronic exposure. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Oxidative stress: A cause and therapeutic target of diabetic complications

Eiichi Araki
Abstract Oxidative stress is defined as excessive production of reactive oxygen species (ROS) in the presence of diminished anti-oxidant substances. Increased oxidative stress could be one of the common pathogenic factors of diabetic complications. However, the mechanisms by which hyperglycemia increases oxidative stress are not fully understood. In this review, we focus on the impact of mitochondrial derived ROS (mtROS) on diabetic complications and suggest potential therapeutic approaches to suppress mtROS. It has been shown that hyperglycemia increases ROS production from mitochondrial electron transport chain and normalizing mitochondrial ROS ameliorates major pathways of hyperglycemic damage, such as activation of polyol pathway, activation of PKC and accumulation of advanced glycation end-products (AGE). Additionally, in subjects with type 2 diabetes, we found a positive correlation between HbA1c and urinary excretion of 8-hydroxydeoxyguanosine (8-OHdG), which reflects mitochondrial oxidative damage, and further reported that 8-OHdG was elevated in subjects with diabetic micro- and macro- vascular complications. We recently created vascular endothelial cell-specific manganese superoxide dismutase (MnSOD) transgenic mice, and clarified that overexpression of MnSOD in endothelium could prevent diabetic retinopathy in vivo. Furthermore, we found that metformin and pioglitazone, both of which have the ability to reduce diabetic vascular complications, could ameliorate hyperglycemia-induced mtROS production by the induction of PPAR, coactivator-1, (PGC-1,) and MnSOD and/or activation of adenosine monophosphate (AMP)-activated protein kinase (AMPK). We also found that metformin and pioglitazone promote mitochondrial biogenesis through the same AMPK,PGC-1, pathway. Taking these results, mtROS could be the key initiator of and a therapeutic target for diabetic vascular complications. (J Diabetes Invest, doi: 10.1111/j.2040-1124.2010.00013.x, 2010) [source]

Mechanism for gastric cancer development by Helicobacter pylori infection

Tsutomu Chiba
Abstract Helicobacter pylori (H. pylori) infection plays a crucial role in the development of gastric cancer. There are two major pathways for the development of gastric cancer by H. pylori infection: the indirect action of H. pylori on gastric epithelial cells through inflammation, and the direct action of the bacteria on epithelial cells through the induction of protein modulation and gene mutation. Both pathways work together to promote gastric carcinogenesis. [source]

4-Hydroxynonenal: A membrane lipid oxidation product of medicinal interest

G. Poli
Abstract A comprehensive focus on 4-hydroxynonenal (HNE) as candidate molecule in a variety of pathophysiological conditions occurring in humans is here provided. Despite an active, now well characterized, metabolism in most cells and tissues, HNE can be easily detected and quantified by means of several methods, although with different sensitivity. Measurements of HNE and/or stable metabolites in biological fluids are already applied as lipid peroxidation/oxidative stress markers in a huge number of human disease processes, often sustained by inflammatory reactions. A primary involvement of this aldehydic product of membrane lipid oxidation in inflammation-related events, as well as in regulation of cell proliferation and growth, in necrotic or apoptotic cell death, appears supported by its marked ability to modulate several major pathways of cell signaling and, consequently, gene expression. The actual knowledge of HNE reactivity, metabolism, signaling and modulatory effect in the various human organs should provide a solid background to the investigation of the aldehyde's contribution to the pathogenesis of human major chronic diseases and would likely promote advanced and oriented applications not only in diagnosis and prevention but also in molecular treatment of human diseases. © 2007 Wiley Periodicals, Inc. Med Res Rev, 28, No. 4, 569,631, 2008 [source]