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PubMed1985

VLDL apolipoprotein B determination in blood serum following precipitation of LDL with polyvinylsulphate.

A method is described for the determination of VLDL apolipoprotein B by radial immunodiffusion (RID) in serum supernatants following precipitation of LDL with polyvinylsulphate. The measurement of VLDL apolipoprotein B is based on the incubation of the polyvinylsulphate supernatant with triglyceride lipase (330 kU/l end concentration) for 12-24 hours at 37 degrees C. A good measure of agreement was found for the corresponding VLDL apolipoprotein B values measured by RID in the polyvinylsulphate supernatants (y) and VLDL apolipoprotein B values calculated as tetramethylurea-insoluble protein in the d less than 1.006 kg/l serum fraction (x) (r = 0.88, y = 0.96x + 0.004, n = 54). Within the tested range of 1.2 mmol/l to 6.7 mmol/l triglycerides, the concentration of apolipoprotein B measured in the polyvinylsulphate supernatant showed a linear relationship. Correlation analysis of VLDL apolipoprotein B values and serum triglycerides and VLDL cholesterol, respectively, showed a good correlation (r = 0.77 and r = 0.75, respectively, n = 54). In the determination of VLDL apolipoprotein B measured in polyvinylsulphate supernatant, a variation coefficient of 4.3% (means = 10.1 mmol/l, n = 20) was found in relation to the precision in the series, and a variation coefficient of 11.4% (means = 5.3 mmol/l, n = 15) in relation to day to day precision.

Apolipoproteins B↗
PubMed1993

Effects of free radical scavengers on cytokine actions on islet cells.

We investigated the effect of free radical scavengers on the actions of cytokines on islet cells. Interferon-gamma and tumor necrosis factor-alpha reduced the nicotinamide adenine dinucleotide content of mouse islet cells; the combination of interferon-gamma (4 x 10(5) U/l) and tumor necrosis factor-alpha (4 x 10(5) U/l) caused nicotinamide adenine dinucleotide reduction by approximately 40%. Dimethyl urea and dimethyl sulfoxide prevented the decrease, whereas superoxide dismutase, catalase, and mannitol were not effective. Dimethyl urea and dimethyl sulfoxide protected islet cells from the synergistic cytotoxic action of interferon-gamma and tumor necrosis factor-alpha. Major histocompatibility complex class II antigen induction by interferon-gamma and tumor necrosis factor-alpha was also inhibited by dimethyl urea and dimethyl sulfoxide, but not by superoxide dismutase, catalase and mannitol. Since superoxide dismutase of a membrane-penetrable form attenuated the class II antigen induction, the inefficiency of superoxide dismutase, catalase and mannitol may be attributable to their inability to penetrate islet cells. These results suggest that the intracellular generation of free oxygen radicals is involved in islet cell cytotoxicity and class II molecule expression by interferon-gamma and tumor necrosis factor-alpha, and that nicotinamide adenine dinucleotide reduction may be associated with islet cell dysfunction caused by the cytokines.

Animals↗
PubMed2001

Fluorometric determination of N-nitroso-N-methylurea with nicotinamide and acetophenone.

A fluorometric method for the determination of N-nitroso-N-methylurea (NMU) has been developed. It is based on the N-methylation reaction of nicotinamide with NMU and a subsequent condensation reaction with acetophenone, followed by an acid treatment to form a fluorescent 2,7-naphthyridine derivative. This method enabled the determination of NMU in the range 0.05 - 2 nmol/200 microl with a relative standard deviation of ca. 3%. It was applied to the determination of NMU formed from a precursor N-methylurea (MU) under simulated gastric conditions containing nitrite and thiocyanate ions at pH 3.0 in the presence of fresh orange juice and milk. NMU was extracted by an Extrelut 20 column and then determined. The mean recoveries of NMU added to the simulated gastric juice containing water, orange juice and milk were 86.5, 85.1 and 69.8%, respectively. The amounts of NMU formed from MU were found to decrease to below 25% in the presence of orange juice and milk.

Acetophenones↗
PubMedDate not supplied

Soil surface structure effect on isoproturon and diflufenican loss in runoff.

Because soil surface structure has a considerable influence on infiltration rate, the sealing process is postulated to have a significant effect on herbicide loss through runoff. We evaluated the effect of degraded soil surface structures on herbicide loss in runoff, and used the experimental data to test the uniform mixing zone concept and two-site sorption kinetics for modeling herbicide transfer to runoff. The experiments were done with simulated rainfall on 10-m2 plots in the field and 0.25-m2 plots in the laboratory after a surface application of 1.5 kg ha(-1) of isoproturon [3-(4-isopropylphenyl)-1,1-dimethylurea] and 0.187 kg ha(-1) of diflufenican [2',4'-difluoro-2-(alpha,alpha,alpha-trifluoro-m-tolyloxy) nicotinanilide]. Isoproturon (IPU) and diflufenican (DFF) concentrations were very high in the first runoff (up to 60 mg L(-1) for IPU and 2 mg L(-1) for DFF) when simulated rainfall was applied 24 h after the treatment. The concentrations decreased very rapidly with total rainfall depth. Degradation of the structural state of the soil surface increased the ratio of pesticide loss to application rate from 0.3 to 10% for IPU and from 0.7 to 7.8% for DFF for a runoff depth of less than 1 mm. The structural state of the soil surface influences the rapidity at which runoff begins after the onset of rain, and the runoff coefficient at steady state. Furthermore, the development of a surface seal seems to limit the depth of soil-runoff interaction and thus influences the dynamics of herbicide mobilization. Concentrations of IPU in the runoff were satisfactorily described with a model incorporating a uniform mixing zone and two-site sorption-desorption.

Forecasting↗
PubMed2005

Poisoning due to urea herbicides.

Urea herbicides, which act by inhibiting photosynthesis, were introduced in 1952 and are now used as pre- and post-emergence herbicides for general weed control in agricultural and non-agricultural practices. Urea herbicides are generally of low acute toxicity and severe poisoning is only likely following ingestion when nausea, vomiting, diarrhoea and abdominal pain may occur. As urea herbicides are metabolised to aniline derivatives, which are potent oxidants of haemoglobin, methaemoglobinaemia (18-80%) has been documented, as well as haemolysis. Treatment is supportive and symptomatic. Methylthioninium chloride (methylene blue) 1-2mg (the dose depending on the severity of features) should be administered intravenously over 5-10 minutes if there are symptoms consistent with methaemoglobinaemia and/or a methaemoglobin concentration >30%.

Herbicides↗
PubMed2004

Pharmacologic evaluation of neurokinin-2 receptor antagonists in the guinea pig respiratory tract.

OBJECTIVE: To evaluate 3 neurokinin-2 (NK2) receptor antagonists on the basis of their ability to block neurokinin A (NKA)-induced contractile responses in various regions of the guinea pig respiratory tract. ANIMALS: 48 clinically normal guinea pigs. PROCEDURE: After euthanasia, the trachea and lungs were removed en bloc. The spirally cut trachea was divided into lower, middle, and upper portions. The main bronchus was spirally cut. A lung strip was cut from the edge of the lung. Tissue strips were mounted in organ baths containing Tyrode solution at 37 degrees C and attached to force transducers interfaced with a polygraph. Lung strips were set at a tension of 1 g; other tissue strips were set at 2 g. After 45 minutes of equilibration, cumulative concentration-response (CR) relationships to graded concentrations of NKA were determined. In the treatment groups, tissues were incubated (30 minutes) with antagonists (MEN 10376, SR 48968, and SR 144190) at 3 concentrations (10(-9), 10(-7), and 10(-5)M) before CR relationships were determined. Effectiveness of SR 48968 against NKA was also tested in vivo. RESULTS: Lung strips failed to contract, but all others responded in a concentration-dependent manner. Bronchial spirals were most sensitive. SR 48968 had the highest pA2 value and effectively blocked NKA. CONCLUSIONS AND CLINICAL RELEVANCE: The bronchial region where airflow resistance is high was the most sensitive to NKA, suggesting the importance of NKA in bronchoconstriction. Nonpeptide antagonists (SR 48968 and SR 144190) were more potent than the peptide antagonist (MEN 10376), indicating their greater therapeutic potential as antiasthmatic agents.

Analysis of Variance↗
PubMed1980

Studies on the protein composition of human serum very low density lipoproteins with particular reference to the presence or absence of late pre-beta lipoprotein (Lp beta).

The amount of tetramethylurea and isopropanol soluble protein, total protein, triglycerides and cholesterol was determined in very low density lipoprotein (VLDL) showing either pre-beta mobility, or combined pre-beta and late pre-beta (Lp beta) or beta-mobility from twenty-two different sera. The ratios cholesterol to triglyceride of the VLDL preparations varied between 0.30 and 1.75. A very strong positive linear correlation between soluble protein and triglycerides over the whole range of VLDL preparations was obtained. There was no difference between sera with and without Lp beta for this relationship. When apolipoprotein B, was plotted against triglycerides, a weak correlation was obtained, and VLDL preparations without Lp beta separated into a group below the regression line, indicating that Lp beta is triglyceride poor in relation to apolipoprotein B. The corresponding plot against cholesterol gave a better correlation but with an even distribution of values of VLDL with and without Lp beta. Total and soluble protein put against cholesterol showed a pronounced tendency of VLDL with pure pre-beta mobility and those with Lp beta mobility to separate into groups, demonstrating that Lp beta is cholesterol rich relative to protein. The findings indicate that Lp beta-containing VLDL may represent the presence of a partly degraded VLDL.

Apolipoproteins↗
PubMed1988

Ketomethylureas. A new class of angiotensin converting enzyme inhibitors.

The design rationale for a new series of tripeptide derived angiotensin converting enzyme (ACE) inhibitors, which we term "ketomethylureas", is described. Analogs of tripeptide substrates (i.e. N-benzoyl-Phe-Ala-Pro) in which the nitrogen atom of the scissile amide bond and the adjacent asymmetric carbon atom of the penultimate amino acid residue are formally transposed give rise to this novel class of inhibitors. The most potent ketomethylureas inhibit ACE with I50 values in the nM range.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1998

Rational design of inhibitors for drug-resistant HIV-1 aspartic protease mutants.

This report describes a method for the assessment of inhibitor binding affinities to wild type HIV-1 aspartic protease and to its drug-resistant mutant forms. We have elaborated a refined method for molecular modeling of the 3D structures of mutant enzymes and enzyme-inhibitor complexes based on the crystal structure of the wild type form, which employs a full thermodynamic cycle. Model complexes of four HIV-1 aspartic protease mutants with ten analogs of the A77003 inhibitor were considered. Predictions of inhibition efficiency, resistance potential, and hydrophilicity of the redesigned A77003 analogs were obtained by employing molecular mechanics for the evaluation of enzyme-inhibitor complexation energy and the polarizable continuum model for the estimation of solvent effects. Simple qualitative indicators for structural modifications aimed at overcoming the emergence of HIV resistance to protease inhibitors and at increasing the bioavailability of pseudopeptide inhibitors are examined. A semi-quantitative method for the description of enzyme-ligand binding and its implications for the rational design of inhibitors with higher binding affinity towards emerging HIV PR mutants is presented.

Aspartic Acid Endopeptidases↗
PubMed2001

Evaluation of cytogenetic effects of isoproturon on the root meristem cells of Allium sativum.

OBJECTIVE: To validate the use of Allium sativum as a reliable test model for genotoxicity, isoproturon, a substituted phenylalkylurea herbicide, was evaluated on the root meristem cells by this plant system. METHOD: Test concentrations were selected by determining EC50 and root tips were exposed to various concentrations for 6 or 24 hr. EC50 concentration was calculated to be 70. 8 ppm for the root growth. In addition to root growth retardation exposure to isoproturon induced morphological changes like discolouration and stiffness of roots. RESULTS: Exposure to various experimental concentrations of isoproturon (35-280 ppm), including EC50, significantly and dose-dependently inhibited the mitotic index and induced chromosome breaks/mitotic aberrations at 6 or 24 hr. CONCLUSION: The frequency of aberrations was found to be decreased in a dose dependent manner at 24 or 48 hr post exposure, however in comparison of control cells the frequency of aberrations was considerably high which indicates genotoxicity potentials of isoproturon. Further, present study also suggests that Allium sativum is a sensitive, efficient, and reliable test system for measuring the genotoxicity potential of environmental chemicals.

Chromosome Aberrations↗
PubMedDate not supplied

Effects of soil variability and weather conditions on pesticide leaching--a farm-level evaluation.

In line with European regulations, Dutch law imposes an environmental threshold of 0.1 microg L(-1) on pesticide concentrations in ground water. During registration, the risk of exceeding this threshold is assessed through simulations for one or a few standard scenarios that do not reflect spatial variability under field conditions. The introduction of precision agriculture, where soil variability is actively managed, can increase control over pesticide leaching. This study presents a step-wise evaluation of the effects of soil variability and weather conditions on pesticide leaching. The evaluation was conducted on a 100-ha arable farm and aimed at identifying opportunities for precision management. As a first step, a relative risk assessment identified pesticides presenting a relatively high risk to the environment. Second, the effect of weather conditions was analyzed through 20 years of simulations for three distinct soil profiles. Results were summarized in cumulative probability plots to provide a probabilistic characterization of historical weather data. The year matching 90% probability (1981) served as a reference to simulate pesticide leaching from 612 soil profiles. After interpolation, areas where concentrations exceeded the environmental threshold were identified. Out of a total of 19 pesticides, isoproturon [N-dimethyl-N'-(4-(1-methylethyl)phenyl)urea], metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one], and bentazon [2,1,3-benzothiadiazin-4(3H)-one, 3-isopropyl-, 2,2-dioxide] showed the highest risk for leaching. Leaching was strongly affected by soil variability at the within-field, field, and farm levels. Opportunities for precision management were apparent, but depended on the scale level at which environmental thresholds were implemented. When legislation is formulated in this issue, the presented step-wise evaluation can serve as a basis for identification and precision management of high-risk pesticides.

Agriculture↗
PubMed2002

Fate and bioaccumulation of isoproturon in outdoor aquatic microcosms.

To gain information concerning the ecotoxicity of isoproturon (IPU) on aquatic ecosystems, six experimental ponds of 5 m3 each were studied. All the experiments were conducted during the summer over two years. Three different types of ecosystems were tested in 1994 and one type of ecosystem was selected and repeated in 1995 with three replicates. In each case, the initial concentration of IPU contamination was set at 10 microg/L. The IPU concentration was determined in the water column and in different species (mainly plants) of the microcosms. A first-order kinetic decrease in IPU concentration was observed in 1994, with half-life ranging from 15 to 35 d, depending on the microcosms. This relatively fast decrease was also confirmed in 1995, but it reached a constant value after two months. A high variability of the IPU concentration was observed in exposed plants, with bioconcentration factors ranging from 100 to 1,200 with large coefficients of variation. The observed plant bioconcentration factors are higher than those predicted by usual numerical models, probably due to the specific binding of IPU on one protein of the photosynthetic apparatus. Our data show that bioconcentration does not occur in mollusks but is important in photosynthetic organisms. Plant bioconcentration and microbial biodegradation are the main processes involved in the IPU decay in our outdoor aquatic microcosms.

Animals↗
PubMed2002

Fate and sublethal effects of isoproturon on mature earthworm (Lumbricus terrestris L.).

This study was conducted to investigate the effects of isoproturon in mature earthworm (Lumbricus terrestris L.) under laboratory condition. Earthworms were exposed to soils contaminated with different concentrations for various duration. Residues were monitored in soil and earthworms after 7, 15, 30, 45, and 60 days of exposure to different isoproturon concentrations. Acute toxicity of isoproturon was determined together with growth rate and total soluble protein content of worms. These parameters were related to isoproturon concentration in soil and earthworms. No lethal effect of isoproturon was observed even at the highest concentration tested (1.4 g/kg soil) after 60 days after treatment. Residues of isoproturon have caused a significant reduction of the growth rate. Additionally a reduction of total soluble protein was observed in all treated worms. Decrease of isoproturon concentration in soil was slow and depended on herbicide initial concentration. In the worms, it increased during the first 15 days and decreased thereafter. This study is suggesting the use of the growth rate of earthworms as biomarker of exposure to isoproturon.

Animals↗