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Biomedical subjects

M Tixier

Publications and source records attributed to M Tixier.

At least 19 recordsLinked to original sources
PubMed2004

Experimental impact of the history of packing on the mean pressure in silos.

The role played by the history of packing in the behaviour of a granular material confined in a column is studied experimentally. The mean pressure applied by the granular assembly to the base is measured as a function of the height of material poured in the column. We obtain reproducible mean vertical normal stress measurements without using a particular procedure to mobilise the wall friction. We focus on the influence of the filling method on the mean vertical normal stress. Filling the column via the edges induces a higher apparent mass of grain than filling it via the centre. Particular attention is devoted to the measurement of the effect of the force sensor stiffness. We show that the lower the base stiffness, the lower the mean pressure on the base. We also vary the packing fraction. We obtain an increasing relation between the apparent mass and the mean packing fraction, and show that this relation depends on the filling method.

Journal Article↗
PubMed1990

Positional specificity of a Lupinus albus lipoxygenase in relation to enzyme concentration and effect of a double dioxygenation product of arachidonic acid.

When arachidonic acid was incubated with Lupinus Albus lipoxygenase, a trienoic fatty acid, 8,15-dihydroperoxy-5,9,11,13-eicosatetraenoic acid was formed in addition to the three HPETEs, 15-HPETE, 8-HPETE and 5-HPETE. The formation of the two major monohydroperoxy acids (15- and 5-HPETE) has been shown to depend on enzyme concentration. At low enzyme concentration (less than or equal to 1 unit), Lupinus Albus lipoxygenase displays its highest regiospecificity at pH 5.8, resulting in the formation of 5-HPETE as the major product (80%). As the enzyme concentration increased, the proportion of 5-HPETE decreased, while the one of 15-HPETE increased. On the other hand, the preincubation of the enzyme with 8,15-diHPETE led to the gradual inactivation of the lipoxygenase activity. The inhibitory effect of 8,15-diHPETE was abolished by using high enzyme concentration. Based on these observations, it is proposed that the trienoic fatty acid, 8,15-diHPETE stemmed from further lipoxygenation of 15-HPETE, blocked the formation of the 15(S) hydroperoxide by Lupinus Albus lipoxygenase but not the formation of 5(S) hydroperoxide.

Arachidonic Acids↗
PubMed1989

Cytotoxicity of arachidonic acid and of its lipoxygenase metabolite 15-hydroperoxyeicosatetraenoic acid on human breast cancer MCF-7 cells in culture.

Monolayer cultures of MCF-7 human breast cancer cell line were treated with arachidonic acid (AA) and 15-L-(s)-hydroperoxyeicosatetraenoic acid (15-L-(s)-HPETE) in a concentration range of 10(-5)-10(-11) M and their relative cytotoxic potential was determined. Both compounds had a time and dose-dependent cytotoxic effect on MCF-7 cells. 15-L-(S)-HPETE, the 15-lipoxygenase product of AA was the most effective.

Arachidonic Acid↗
PubMed1989

Properties of a Lipoxygenase in Green Algae (Oscillatoria sp.).

A lipoxygenase preparation was obtained from green algae Oscillatoria sp. and was shown to differ from previous described lipoxygenases in the positional specificity and pH characteristics of the dioxygenation reaction. The enzyme had a pH optimum at 8.8 and was inactive at pH 6. Oscillatoria lipoxygenase converted linoleic acid into two products: 13-hydroperoxylinoleic acid (52%) and 9-hydroperoxylinoleic acid (48%). The molecular weight of the enzyme was estimated at 124,000. Esculetin was found to be the best inhibitor of the enzyme activity.

Journal Article↗
PubMed1989

An Enzymatic Conversion of Lipoxygenase Products by a Hydroperoxide Lyase in Blue-Green Algae (Oscillatoria sp.).

An enzyme has been isolated from blue-green algae Oscillatoria sp. which utilizes the product, 13-hydroperoxy-9, 11-octadecadienoic acid (13-HPOD), of lipoxygenase for its substrate. This enzyme, termed hydroperoxide lyase, converts the conjugated diene 13-hydroperoxide of linoleic acid to 13-oxotrideca-9, 11-dienoic acid. The structure of the latter has been determined by ultraviolet spectroscopy and mass spectrometry. 9-HPOD is not a substrate for this enzyme. The hydroperoxide lyase from Oscillatoria sp. has a maximum of activity at pH 6.4 and 30 degrees C. The molecular weight of the enzyme was estimated at 56,000. The enzyme was not inhibited by BW 755C, but was inhibited by molecules containing more than one hydroxyl group. Quercetin was found to be the best inhibitor of the enzyme activity. The purified hydroperoxide lyase from Oscillatoria sp. showed an apparent K(m) of 7.4 micromolar and a V(max) of 35 nanomoles per minute per milligram of protein for 13-HPOD. An enzymatic pathway for the biogenesis of oxodienoic acid from linoleic acid is proposed. This involves the sequential activity of lipoxygenase and hydroperoxide lyase enzymes.

Journal Article↗
PubMed1989

Mitogenic effect of estradiol on MCF-7 human breast cancer cells can be modulated by serum.

The MCF-7 human breast cancer cell line responds to estradiol stimulation in vitro by increased proliferation only if prolonged subcultures in dextran-coated charcoal-treated fetal calf serum have been made previously. This growth stimulation is not obtained when cells are grown in medium containing 5% untreated fetal calf serum. We describe here the culture conditions under which we obtain a reproducible estradiol effect on cell growth.

Breast Neoplasms↗
PubMed1986

Effect of isoquinoline alkaloids on soybean lipoxygenase activity in vitro.

Novel isoquinoline alkaloids were evaluated for their effect on the kinetics of a soybean lipoxygenase type I using linoleic acid as substrate. Some of these alkaloids were found to increase the initial reaction velocity, this property seems related to phenolic groups present in the molecule. The effect of these compounds on the soybean lipoxygenase activity was compared to that of others products which are known to affect this reaction. A reaction mechanism is then proposed: it appeared, in this reaction a correlative structure-activity of phenolic compounds we tested.

Alkaloids↗
PubMed1986

Amino Acids Content in Germinating Seeds and Seedlings from Castanea sativa L.

During germination the chestnut (Castanea sativa L.) var ecotype 33 accumulates a large amount of asparagine in the cotyledons. This compound also accumulates in the growing axis:shoots and roots. In the cotyledons, gamma-aminobutyrate (GABA) represents a major amino compound during germination and early seedling growth. In young seedlings, 35 days old, arginine predominates over the other soluble amino acids, particularly in roots. Five enzymic activities involved in arginine and GABA have been measured in the storage organ of the seed: arginase and ornithine carbamyltransferase decrease during germination indicating the slowing down of the urea cycle. In contrast, ornithine aminotransferase increases. Glutamate decarboxylase is particularly active about 21 days after imbibition and GABA aminotransferase activity decreases during germination. These two activities are in good agreement with the likely transport of GABA from cotyledons to growing axis. Asparagine, arginine, and GABA are the three amino compounds obviously involved in the mobilization of nitrogen reserves in the germinating chestnut seeds Castanea sativa.

Journal Article↗
PubMed1984

[The frequency of chromosome abnormalities in farm animals and their economic consequences].

Examinations during the last two decades of the chromosome complements of various species of domestic animals have revealed the existence of a considerable number of abnormalities, including inherited rearrangements: approximately 20 in cattle, 15 in pigs (predominantly reciprocal translocations), 3 in sheep, 2 in horses (predominantly monosomy X), and 1 in goats. (The accumulation of data on the frequency of such abnormalities and evaluation of their effects on reproductive performances of carriers of inherited rearrangement depends on a number of factors including the use of artificial insemination, number or progeny per sire or dam, and differences in generation intervals of the species concerned). The economic value of the cytogenetic findings depends on the degree of exchange of information between the breeders and the cytogenetics laboratories. An example of a successful collaboration is a Swedish study of a centric fusion translocation in Swedish Red and White cattle, one that affects chromosomes 1 and 29. There, the fertility-reducing effects of the translocation led to a loss of approximately $250,000. Recognition of the significance of the translocation prompted a search for carrier bulls and their elimination from the artificial insemination units. In swine, in which artificial insemination is used much less than in cattle, data on the frequency of reciprocal translocations in general must be obtained from the farms themselves. The main effect of an inherited chromosome rearrangement is a reduction in the number of offspring, perhaps to 50%, i.e., five piglets per litter.(ABSTRACT TRUNCATED AT 250 WORDS)

Animal Husbandry↗
PubMed1978

[Characterization and quantification by impulse analysis of sugar regulation disorders in man].

Proposed model offers three transfer functions answering to a second order hypothesis and allowing to study separately blood sugar evolution and insulin release or synthesis functions by cell B. The model separates subjects in several classes (normals, chemical diabetes and patent insulin-dependent or independent diabetes) and quantifies treatment efficiency by its effects on blood sugar regulation.

Blood Glucose↗