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At least 253 records · Page 14Linked to original sources

PubMed2000

Mobility of isoproturon from an alginate-bentonite controlled release formulation in layered soil.

The mobility of isoproturon [3-(4-isopropylphenyl)-1,1-dimethylurea] from an alginate-based controlled release (CR) formulation was investigated by using soil columns. A layered bed system simulating the typical arrangement under a plastic greenhouse, which is composed of sand, peat, amended soil and native soil was used. The CR formulation was based on sodium alginate (1.87%), isoproturon (1.19%), natural bentonite (3.28%), and water (93.66%), and was compared to technical grade isoproturon. The use of the alginate-bentonite CR formulation produced less vertical mobility of the active ingredient as compared to the technical product. There was no presence of herbicide in the leachate when the alginate-bentonite CR formulation was used. However, 0.90% of isoproturon appeared when the treatment was carried out with technical grade material. Isoproturon mobility was modelled using the programme CMLS, which showed the peat layer to retard pesticide leaching. Analysis of the soil columns showed the highest isoproturon concentration in the peat layer.

Adsorption↗

PubMed2000

Fate of seven pesticides in an aerobic aquifer studied in column experiments.

The fate of selected pesticides (bentazone, isoproturon, DNOC, MCPP, dichlorprop and 2,4-D) and a metabolite (2,6-dichlorobenzamide (BAM)) was investigated under aerobic conditions in column experiments using aquifer material and low concentrations of pesticides (approximately 25 microg/l). A solute transport model accounting for kinetic sorption and degradation was used to estimate sorption and degradation parameters. Isoproturon and DNOC were significantly retarded by sorption, whereas the retardation of the phenoxy acids (MCPP, 2,4-D and dichlorprop), BAM and bentazone was very low. After lag periods of 16-33 days for the phenoxy acids and 80 days for DNOC, these pesticides were degraded quickly with 0.-order rate constants of 1.3-2.6 microg/l/day. None of the most probable degradation products were detected.

2,4-Dichlorophenoxyacetic Acid↗

PubMed2004

Seasonal changes in the sensitivity of river microalgae to atrazine and isoproturon along a contamination gradient.

A study was undertaken to investigate the environmental impact of herbicides on natural communities of freshwater periphyton and phytoplankton in the river Ozanne and in related nearby water reservoirs, including both pristine and pesticide- (atrazine and isoproturon) contaminated stations. The microalgal toxicity of both herbicides was investigated by short-term studies, using the in vivo fluorescence pattern to perform dose-effect experiments. The taxonomic composition of the communities sampled was assessed by microscopy and by HPLC pigment analysis. The EC50 (periphyton) or EC125 (phytoplankton) values, calculated using in vivo fluorescence endpoints, increased with the herbicide concentration found in the water. In contrast, the structure of the algal communities (periphyton) inhabiting the contaminated stations seemed to be permanently affected when compared to the reference community. A 'memory effect' could be detected, both in herbicide sensitivity and in the structure of periphytic communities that persisted even when peak contaminations had disappeared. This study shows that the response of algal communities is likely to reflect past selection pressures, and suggests that the function and structure of a community could both be modified by the persistent or repeated presence of microcontaminants in natural environments. We could use short-term ecotoxicological tests on freshwater microalgae to assess the effects of past temporary contaminations by agricultural pesticides, and combining this with diversity indices could make it possible to assess the ecotoxicological risk of herbicide contamination even when a complete chemical analysis of the contamination is not feasible.

Agriculture↗

PubMed1999

The role of intermolecular interactions: studies on model systems for bacterial biofilms.

The mechanical stability of biofilms and other microbial aggregates is of great importance for both the maintenance of biofilm processes and the removal of undesired biofilms. The binding forces are weak interactions such as London dispersion forces, electrostatic interactions and hydrogen bonds. In a first attempt to rank their contribution, the viscosity of solutions of extracellular polymeric substances (EPS) from a mucoid strain of Pseudomonas aeruginosa is measured. In order to distinguish the binding forces, substances are chosen which individually address the different types of bonds. Polyacrylic acid is identified as a suitable model system for EPS when molecular interactions are studied. Electrostatic interactions and hydrogen bonds are found to be the dominating forces among macromolecules within the biofilm.

Acrylic Resins↗

PubMed1999

Effect of lysine modification on the conformation and indomethacin binding properties of human serum albumin.

In order to study the involvement of lysine residues of human serum albumin (HSA) in the binding of indomethacin, HSA was treated with different molar excess of acetic anhydride, succinic anhydride and O-methylisourea which resulted in differently modified preparations: 30%, 62% and 87% acetylated, 20%, 34%, 64% and 78% succinylated and 21%, 43% and 86% guanidinated HSAs. All the preparations were found to be homogeneous with respect to charge as well as size as judged by polyacrylamide gel electrophoresis and gel filtration on a Seralose-6B column. Hydrodynamic and circular dichroic results showed that pronounced conformational changes (both tertiary and secondary structures) were induced in the maximally acetylated (87%) and succinylated (78%) preparations. On the other hand, guanidinated preparations showed no expansion in the hydrodynamic volume. The percent decrease in alpha-helical content was 34% for 87% acetylated, 31% for 78% succinylated and 10% for 86% guanidinated HSAs. A significant increase in the values of Stokes radii and frictional ratios (from 3.43 nm and 1.29 for native HSA to 4.07 nm and 1.52 for 87% acetylated and 4.35 nm and 1.60 for 78% succinylated HSAs, respectively) was also noticed in these highly modified preparations. Fluorescence quench titration results obtained at pH 7.4 and ionic strength 0.15 showed that only 54.1% and 64.7% binding of indomethacin at 4:1 drug/protein molar ratio was retained by 87% acetylated and 78% succinylated HSAs, respectively, as compared to 91% retention in binding in 86% guanidinated preparation. No reversal in the binding of drug to 87% acetylated and 78% succinylated HSA preparations was observed on increasing the ionic strength to 1.0. Therefore, it seems that one or two critical lysine residue(s) that can form salt linkage with the carboxyl group of indomethacin, was (were) probably modified in these preparations. A small decrease in the binding of drug to the guanidinated preparation also confirms the involvement of positive charge, probably contributed by lysine residue(s), in the binding of indomethacin to HSA.

Acetic Anhydrides↗

PubMed1997

Biochemical and pharmacological activities of SR 144190, a new potent non-peptide tachykinin NK2 receptor antagonist.

(R)-3-(1-[2-(4-benzoyl-2-(3,4-difluorophenyl)-morpholin-2-yl)- ethyl]-4-phenylpiperidin-4-yl)-1-dimethylurea (SR 144190) is a new non-peptide antagonist of tachykinin NK2 receptors. SR 144190 potently and selectively inhibited neurokinin A binding to NK2 receptors from various species, including humans. In in vitro functional assays, it was a potent, selective and competitive antagonist of NK2 receptors with apparent affinities (pA2 values) between 9.08 and 10.10. In vivo, SR 144190 blocked [Nle10]neurokinin A-(4-10)-induced bronchoconstriction in guinea pigs (ID50 = 21 micrograms kg-1 i.v. and 250 micrograms kg-1 i.d.) and [beta Ala8]neurokinin A-(4-10)-induced urinary bladder contraction in rats (ID50 = 11 micrograms kg-1 i.v. and 190 micrograms kg-1 i.d.). It prevented citric acid-induced cough and airway hyperresponsiveness to acetylcholine in guinea pigs (1 mg kg-1 i.p.) as well as castor oil-induced diarrhoea in rats (0.01-10 micrograms kg-1 s.c. or p.o). Finally, it blocked the turning behaviour induced by intrastriatal injections of [Nle10]neurokinin A-(4-10) in mice (ID50 = 3 micrograms kg-1 i.v. and 16 micrograms kg-1 p.o.).

Animals↗

PubMed2001

Role of tachykinin receptors in the central processing of afferent input from the acid-threatened rat stomach.

Noxious challenge of the rat gastric mucosa by hydrochloric acid (HCl) is signalled via vagal afferent neurons to several brain nuclei in which tachykinins and tachykinin receptors are present. Therefore, we tested whether tachykinin receptor antagonists would modify the central transmission of input from the acid-threatened stomach. Neuronal excitation was visualized by in situ hybridization autoradiography (ISH) of c-fos messenger ribonucleic acid (mRNA) 45 min after intragastric (IG) administration of HCl (0.5 M; 10 ml/kg). This stimulus has previously been shown to cause neurons in the nucleus tractus solitarii (NTS), lateral parabrachial nucleus (LPB), paraventricular (Pa) nuclei, supraoptic (SO) nucleus, central amygdala (CeA), area postrema (AP), subfornical organ (SFO) and habenula (Hb) to express c-fos mRNA. Intraperitoneal (IP) pretreatment with the NK1 receptor antagonist GR-205,171 (3 mg/kg) attenuated the acid-induced transcription of c-fos mRNA in NTS and augmented it in SFO. The NK2 receptor antagonist SR-144,190 (0.1 mg/kg, IP) had no effect. Subcutaneous administration of the NK3 receptor antagonist SB-222,200 (20 mg/kg) reduced the c-fos mRNA response in AP and SFO and enhanced it in Hb. These data show that the transmission of input from the acid-threatened stomach in distinct brain nuclei involves tachykinins acting at NK1 and NK3 receptors, but not NK2 receptors.

Afferent Pathways↗

PubMed2001

Evaluating non-equilibrium solute transport in small soil columns.

Displacement studies on leaching of bromide and two pesticides (atrazine and isoproturon) were conducted under unsaturated steady state flow conditions in 24 small undisturbed soil columns (5.7 cm in diameter and 10 cm long) each collected from two sites differing in soil structure and organic carbon content in North Germany. There were large and irregular variabilities in the characteristics of both soils, as well as in the shapes of breakthrough curves (BTCs) of different columns, including some with early breakthrough and increased tailing, qualitatively indicating the presence of preferential flow. It was estimated that one preferential flow column (PFC) at site A, and four at site B, contributed, respectively to 11% and 58% of the accumulated leached fraction and to more than 80% of the maximum observed standard deviation (SD) in the field-scale concentration and mass flux of pesticides at two sites. The bromide BTCs of two sites were analyzed with the equilibrium convection-dispersion equation (CDE) and a non-equilibrium two-region/mobile-immobile model. Transport parameters of these models for individual BTCs were determined using a curve fitting program, CXTFIT, and by the time moment method. For the CDE based equilibrium model, the mean values of retardation factor, R, considered separately for all columns, PFCs or non-preferential flow columns (NPFCs) were comparable for the two methods; significant differences were observed in the values of dispersion coefficients of two sites using the two estimation methods. It was inferred from the estimated parameters of non-equilibrium model that 5-12% of water at site A, and 12% at site B, was immobile during displacement in NPFCs. The corresponding values for PFCs of two sites were much larger, ranging from 25% to 51% by CXTFIT and from 24% to 72% by the moment method, suggesting the role of certain mechanisms other than immobile water in higher degrees of non-equilibrium in these columns. Peclet numbers in PFCs of both sites were consistently smaller than five, indicating the inadequacy of the non-equilibrium model to incorporate the effect of all forms of non-equilibrium in PFCs. Overall, the BTCs of individual NPFCs, PFCs and of field average concentration at the two sites were better reproduced with parameters obtained from CXTFIT than by the moment method. The moment method failed to capture the peak concentrations in PFCs, but tended to describe the desorption and tail branches of BTCs better than the curve fitting approach.

Atrazine↗

PubMed2001

Spatial variability in the degradation rate of isoproturon in soil.

Thirty samples of soil were taken at 50-m intersections on a grid pattern over an area of 250 x 200 m within a single field with nominally uniform soil characteristics. Incubations of isoproturon (3-(4-isopropylphenyl)-1,1-dimethylurea) under standard conditions (15 degrees C; -33 kPa soil water potential) indicated considerable variation in degradation rate of the herbicide, with the time to 50% loss (DT50) varying from 6.5 to 30 days. The kinetics of degradation also varied between the sub-samples of soil. In many of them, there was an exponential decline in isoproturon residues; in others, exponential loss was followed by more rapid rates of decline; in a few soil samples, rapid rates of loss began shortly after the start of the incubations. In more detailed studies with soils from a smaller number of sub-sites (20), measurements were again made of isoproturon degradation rate, and the soils were analysed for organic matter content, pH, and nutrient status (N, P, K). Measurements were also made of isoproturon adsorption by the soils and of soil microbial biomass. Patterns of microbial metabolism were assessed using 95 substrates in Biolog GN plates. Soils showing rapid biodegradation were generally of higher pH and contained more available potassium than those showing slower degradation rates. They also had a larger microbial biomass and greater microbial metabolic diversity as determined by substrate utilisation on Biolog GN plates. The implications of the results for the efficacy and environmental behaviour of isoproturon are discussed.

Adsorption↗

PubMed2001

Effect of isoproturon pretreatment on the biochemical toxicodynamics of anilofos in male rats.

Anilofos and isoproturon are important herbicides of organophosphorus and substituted phenylurea groups, respectively. Isoproturon is an inducer of hepatic drug-metabolizing enzymes. Animals and humans have the potential to be exposed to the mixture of these intentionally introduced environmental xenobiotics, but toxicological interactions between these herbicides are not known. Effects of isoproturon pretreatment (675 mg/kg/day for 3 consecutive days) on the toxic actions of anilofos administered orally as a single dose (850 mg/kg) were evaluated by determining some biochemical attributes in blood (erythrocyte/plasma), brain and liver of rats. Anilofos or isoproturon alone or in combination failed to produce any noticeable signs of cholinergic hyperactivity and behavioural alterations. Isoproturon did not potentiate the anticholinesterase action of anilofos in blood and liver. Inhibition of brain acetylcholinesterase was significantly protected. No significant alteration in anilofos-mediated production of lipid peroxidation was observed in erythrocyte and brain of isoproturon-pretreated rats, but it was significantly increased in liver. Anilofos did not affect GSH and GST. The isoproturon-mediated increase in GSH levels of brain (threefold) and liver (3.6-fold) was also not affected following combined administration. GST activity was increased in liver of rats given isoproturon alone (fourfold) or in combination with anilofos (2.8-fold). Activities of total ATPase, Mg2+-ATPase and Na+-K+-ATPase were not affected in rats given either anilofos alone or herbicides in sequence. With these treatments, there were no alterations in the protein content of plasma, brain and liver. Overall findings of the study indicate that isoproturon pretreatment does not alter the toxicity of anilofos, the GSH-GST metabolic pathway may not have a significant implication in the detoxification of anilofos and the production of a reactive oxygen species may be a factor in mediating anilofos toxicity.

Adenosine Triphosphatases↗

PubMed2002

Rheological study on lysozyme/tetramethylurea viscoelastic matrices.

Rheological properties of lysozyme viscoelastic matrices resulting from a sol-gel transition taking place in organic/aqueous media at room temperature were investigated. Gel-like structures, of transparent appearance, developed out of lysozyme (5.0 mmol/dm(3)) dispersed in tetramethylurea (TMU)/water binary mixtures, at TMU mass fraction (w) ranging from w(TMU) 0.6 to 0.9. The wide linear viscoelastic region (LVR) observed, up to strains of 10%, was invariant throughout the TMU concentration range investigated, indicating that the 3D structures of protein matrices, although fragile, are quite flexible and able to withstand great deformation before rupture. Storage (G') and loss (G") moduli continuously increased with increasing TMU concentration, the former at a greater rate, consequently leading systems to a decrease in the loss angle, tandelta. For gels developed out of binary systems at w(TMU)=0.9, creep curves revealed behaviour that very nearly approaches that of a perfect elastic solid. Although gelification under the experimental conditions employed is macroscopically accomplished in a time interval that does not exceed 24 h (for the gel developed out of the solvent mixture of lowest TMU concentration, w(TMU)=0.6), a slight decrease in loss angle can still be detected after that period. Such changes, however, have no effect on the LVR. Relaxation tests indicate that systems comprise at least two dynamically distinct contributions.

Elasticity↗

PubMed2002

Lysozyme viscoelastic matrices in tetramethylurea/water media: a small angle X-ray scattering study.

Semi-solid viscoelastic matrices produced out of lysozyme in organic/aqueous media [tetramethylurea (TMU)/water] were characterized by small angle X-ray scattering (SAXS). The scattering curves were modeled in their form and interference factors. Radii of gyration of scattering particles were found to undergo a dramatic increase from 14 A in water to approximately 44 A in the matrices. Average correlation distances d=155 A were consistently verified for the scattering particles in the matrices, irrespective of solvent composition (in the 0.6<or=w(TMU)<or=0.8 range), in contrast to what is observed in water (d=62 A). At w(TMU)=0.9, however, a slight increase in R(g) (to R(g)=49 A) leads to interdigitation with the apolar prevailing medium of the matrix leading to the loss of the interference effect. Low dimensionality derived from the modeling procedure could be taken to indicate mass fractal character of the unfolded species, although polydispersion of samples could also have some contribution to that result. Despite the very significant shape distortion of the unfolded protein forms in the matrices, they still retain considerable globular character, as indicated by the Kratky plots obtained. The morphological results obtained in this work are compatible with the dynamical behavior displayed by the systems.

Animals↗

PubMed2003

Heterogeneous photocatalysed degradation of a herbicide derivative, isoproturon in aqueous suspension of titanium dioxide.

Heterogeneous photocatalysed degradation of a herbicide derivative, N-(4-isopropylphenyl)-N',N'-dimethylurea (Isoproturon, 1) was investigated in aqueous suspensions of titanium dioxide by monitoring the change in absorption intensity and depletion in Total Organic Carbon content as a function of irradiation time. The degradation kinetics was studied under different conditions such as pH, catalyst concentration, substrate concentration, different types of TiO(2) and in the presence of electron acceptors such as hydrogen peroxide (H(2)O(2)), potassium bromate (KBrO(3)) and potassium persulphate (K(2)S(2)O(8)) besides molecular oxygen. The degradation rates were found to be strongly influenced by all the above parameters. The photocatalyst Degussa P25 was found to be more efficient as compared with other photocatalysts. An attempt was made to identify the degradation product through GC-MS analysis technique.

Catalysis↗

PubMed1998

Facilitation of striatal acetylcholine release by dopamine D1 receptor stimulation: involvement of enhanced nitric oxide production via neurokinin-2 receptor activation.

The regulation of striatal cholinergic function by dopamine D1 receptor activation was examined in vivo in urethane-anaesthetized rats with microdialysis probes. Extracellular acetylcholine levels were enhanced by activation of D1 receptors either directly by a striatal application of the D1 receptor agonist (+)-SKF-38393 (3 microM) or indirectly by the release of dopamine evoked by striatal application of neurotensin (0.1 microM) under D2 receptor blockade. SR 144190, a new potent and selective non-peptide neurokinin-2 receptor antagonist (0.03-1 mg/kg, i.p.), dose-dependently reduced the acetylcholine release induced by (+)-SKF-38393 or neurotensin. Furthermore, intrastriatal application of SR 144190 (1 nM) blocked the increase in acetylcholine release induced by the local application of (+)-SKF-38393 (3 microM), neurokinin A (1 microM) or substance P (1 microM). Finally, a role for nitric oxide in mediating the effects of D1 neurokinin-2 receptor activation on acetylcholine release is proposed since local infusion of the competitive inhibitor of nitric oxide synthase, N(G)-monomethyl-L-arginine (0.01-10 microM), blocked the increase in acetylcholine release induced by (+)-SKF-38393 (3 microM), neurotensin (0.1 microM) or neurokinin A (1 microM) without affecting the enhancing effect of the neurokinin-1 agonist septide (0.1 microM).

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

PubMed2002

Characterization of the in vitro adhesion of Actinobacillus pleuropneumoniae to swine alveolar epithelial cells.

Actinobacillus pleuropneumoniae biovar 1 serotypes 2, 5a, 9 and 10 strains were tested for their ability to adhere to alveolar epithelial cells in culture. For the serotypes 5a, 9 and 10 strains, optimal adherence was observed after growth of bacterial cells in a NAD-restricted medium (0.001% NAD). This condition was also associated with the expression of a 55 kDa outer membrane protein (OMP) and of fimbriae. For the serotype 2 strain, adherence and expression of fimbriae and a 55 kDa OMP was less influenced by the growth conditions. The N-terminal amino acid sequence of the 55 kDa OMP had no homology with any known sequence, suggesting that it is an as yet unknown protein. Adherence capabilities were significantly reduced following treatment of the bacteria with proteolytic enzymes or heat. These findings suggest that proteins are involved in adhesion. The hydrophobic bond-breaking agent tetramethylurea was unable to inhibit the adherence of A. pleuropneumoniae to alveolar epithelial cells. Treatment of the bacteria with sodium metaperiodate resulted in lower adhesion scores for the serotypes 2 and 9 strains but the inhibition of adhesion was clearly lower than after treatment with proteolytic enzymes. This indicates that, besides proteins, carbohydrates might also be involved in adhesion of A. pleuropneumoniae to alveolar epithelial cells. The finding that inhibition of adhesion was very high when bacteria were treated with a combination of sodium metaperiodate and pronase also suggests that more than one adhesin is involved.

Actinobacillus pleuropneumoniae↗

PubMed1986

1,10 phenanthroline, a metal chelator, protects against alloxan- but not streptozotocin-induced diabetes.

The iron chelator, 1,10-phenanthroline (Phen), which inhibits hydroxyl radical formation, was tested in vitro and in vivo against alloxan and streptozotocin (STZ) cytotoxicity. Phen injection reduced the severity of alloxan-induced diabetes in rats and attenuated alloxan-induced toxicity in human fibroblasts (VA 13 line) in culture. These protective effects were not observed against STZ toxic action. These results are consistent with the hypothesis that hydroxyl radicals, generated via an iron-catalyzed reaction, induce the alloxan but not the STZ diabetogenic effects.

Alloxan↗

PubMed2001

Oligomerization of Escherichia coli enterotoxin b through its C-terminal hydrophobic alpha-helix.

Using a chemical cross-linker and gel electrophoresis or a dot blot overlay assay, we studied protein-protein interaction of STb toxin, a 48-residue amphiphilic polypeptide causing intestinal disorders. For the first time, we report on the oligomerization property of STb. This enterotoxin forms hexamers and heptamers in a temperature-independent fashion in presence or absence of its receptor (sulfatide) anchored in a 50-nm liposome or as a free molecule. Full STb structure integrity is necessary for its oligomerization as this process is not observed under reducing conditions in the presence of beta-mercaptoethanol. STb treatment with tetramethylurea (TMU) and different detergents prevented oligomerization. Site-directed mutagenesis decreasing overall STb hydrophobicity in the hydrophobic alpha-helix resulted in the incapacity to form oligomers. Taken together, these data suggest that the C-terminal hydrophobic alpha-helix corresponds to the domain of STb-STb inter-binding where hydrophobic interaction is involved.

Amino Acid Sequence↗

PubMed2004

Simultaneous multi-analyte determination of estrone, isoproturon and atrazine in natural waters by the RIver ANAlyser (RIANA), an optical immunosensor.

In most medical and environmental applications of biosensors, only single analytes are determined. However, the monitoring of several analytes is obviously preferable in order to gather more information about the sample under analysis. In line with this, different technologies are being developed to obtain multi-analyte sensors. In this paper, an analytical method for the simultaneous determination of three different contaminants-atrazine, isoproturon, and estrone-in natural waters by using an optical immunosensor prototype, the so-called "RIver ANAlyser" (RIANA), is described. RIANA is based on a rapid solid-phase fluoroimmunoassay that takes place at an optical transducer chip. The transducer surface is chemically modified with three analytes derivatives placed in different discrete locations. The sensor surface can be regenerated thus allowing the performance of several measurements with the same transducer. Each test cycle, including one regeneration step, is accomplished in 15 min. Detection limits achieved were 0.155, 0.046, and 0.084 microg/l, for atrazine, isoproturon, and estrone, respectively. Satisfactory repetition, with relative standard deviations between 1.06 and 6.98%, was obtained. Excluding a minor non-specifical binding of the isoproturon antibodies, no cross-reactivity effects were observed. Matrix effects were significant only in the case of wastewater samples. Biosensor measurements were validated using conventional liquid chromatography-mass spectrometry. The results obtained with both techniques were in good agreement.

Atrazine↗