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J P Nicolas

Publications and source records attributed to J P Nicolas.

At least 19 recordsLinked to original sources
PubMed2005

A molecular dynamics study of an archaeal tetraether lipid membrane: comparison with a dipalmitoylphosphatidylcholine lipid bilayer.

Molecular dynamics simulations of an archaeal membrane made up of bipolar tetraether lipids and a dipalmitoylphosphatidylcholine (DPPC) lipid membrane were performed and compared for the first time. The simulated archaeal membrane consists of a pure monolayer of asymmetrical lipids, analogous to the main polar lipid [MPL; Swain, M., Brisson, J.-R., Sprott, G.D., Cooper, F.P., and Patel, G.B., (1997) Identification of beta-L-Gulose as the Sugar Moiety of the Main Polar Lipid of Thermoplasma acidophilum, Biochim. Biophys. Acta 1345, 56-64] found in T. acidophilum, an extremophile archaeal organism. This simulated membrane lipid contains two cyclopentane rings located on one of the two aliphatic chains of the lipid. The archaeal membrane is simulated at 62degreesC, slightly above the optimal growth temperature of T. acidophilum. We compared the organization of this tetraether lipid monolayer with a DPPC bilayer simulated at 50degreesC, both of them being modeled in a partially hydrated state. Our results assess the singularity of the tetraether lipid organization, in particular the influence of the spanning structure on the molecular ordering within the archaeal membrane.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2004

Molecular dynamics study of the n-hexane-water interface: towards a better understanding of the liquid-liquid interfacial broadening.

By molecular dynamics simulations, we have studied the hydrophilic-hydrophobic interface between water and n-hexane liquid phases. For all temperatures studied our computed interfacial tension agrees very well with the experimental value. However, the interfacial width calculated from capillary wave theory systematically overestimates the width obtained from fitting either the total density or composition profile. We rationalize the applicability of capillary wave theory for our system by reconsidering the usual value taken for the correlation length. This is motivated by the presence of order at the interface. Possible implications for recent experimental studies on the structure of model alkane-water interfaces are discussed, including the significance of the intrinsic width parameter.

Journal Article↗
PubMed2004

[Food allergy: effect of proteins-lipids and proteins-polysaccharides interactions].

The most widely used ingredients in food formulation are proteins, lipids and polysaccharides. Proteins-lipids and proteins-polysaccharides interactions play a key role in the structure, stability, sensorial and nutritional properties of formulated foods. The objective of the present study is to highlight the importance of proteins-lipids and proteins-polysaccharides interactions, on the immuno-reactivity of allergenic proteins. Two models have been studied, on the one hand refined and not refined oils (soya and sunflower) and soya lecithin, on the other hand mixtures based on peanut proteins and polysaccharides (arabic gum, pectin, xylan). STUDY OF OILS: We have extracted proteins, using a PBS buffer, from refined and not refined oils from soya, sunflower and from soya lecithin, determined protein concentrations and identified allergenic proteins using SDS-PAGE electrophoresis and immuno-blotting. Phospholipids are determined by atomic absorption spectrometry. The protein determination and SDS-PAGE show the presence of a higher amount of proteins in not refined oils and lecithin as compared to refined oils. An important amount of proteins associated to phospholipids are eliminated by degumming on the form of lecithin. On the other hand, residual proteins from refined oils are accompanied by phospholipids. Immuno-blots reveal the presence of a 56 kDa allergen in oils issued from soya seeds and soya lecithin, and the presence of a 67 kDa allergen in oils issued from sunflower seeds. We conclude that the presence or elimination of proteins, especially allergens from oils is linked to amphiphilic association to phospholipids. STUDY OF PEANUT PROTEINS-POLYSACCHARIDES MIXTURES: We have digested in vitro proteins in a dialysis bag using a multi-enzymatic method and characterized proteins and peptides using SDS-PAGE electrophoresis and immuno-blotting. Our results confirm that peanut proteins alone are digested by proteases and that a number of large peptides still have epitopes recognized by anti-peanut proteins antibodies. Our results also show that the presence of polysaccharides changes the peptidic profile after digestion and that, depending on the polysaccharide type, smaller or larger peptides can be obtained in the dialysis bag. Smaller peptides are obtained using pectin whereas larger peptides are obtained using arabic gum and xylan. In the latter case, an increasing amount of peptides reacts to antibodies. Our first observations clearly show the need to better understand modifications of proteins allergenicity induced by the presence of other ingredients such as polysaccharides and lipids, in relation to technological treatments.

Allergens↗
PubMed2003

Molecular dynamics simulation of surfactin molecules at the water-hexane interface.

The dynamics of surfactin, a lipopeptide surfactant from Bacillus subtilis, has been studied by molecular dynamics at different interfacial concentrations in a water-hexane medium reproducing a hydrophilic/hydrophobic biphasic system. The shapes and orientations of surfactin molecules, as hydrogen bonds and Ramachandran angles, have been recorded to investigate the environment effect on the molecular structure. We demonstrate that the peptidic backbone can exhibit a large flexibility and that conformational motions and structural fluctuations depend strongly on the interfacial concentration. Moreover, we have measured the surface activity of this biosurfactant by computing the interfacial tension and lateral and rotational diffusion coefficients.

Algorithms↗
PubMed2002

Obesity is associated with decreasing levels of the circulating soluble leptin receptor in humans.

OBJECTIVE: Leptin plays a major role in the regulation of body weight. It circulates in both free and bound form. One of the leptin receptor isoforms exists in a circulating soluble form that can bind leptin. In the present study, we measured the soluble leptin receptor (SLR) levels in lean and obese humans. We investigated the relationship between plasma SLR levels, plasma leptin levels and the degree of obesity. We also examined whether SLR concentrations could be modulated by fat mass loss induced by a 3 month weight-reducing diet. SUBJECTS: A total of 112 obese (age 18-50 y; body mass index (BMI) 30-44 kg/m2; 23 men and 89 women), 38 overweight (age 19-48 y; BMI 25-29 kg/m2; 10 men and 28 women) and 63 lean (age 18-50 y; BMI 17-24 kg/m2; 16 men and 47 women) humans. MEASUREMENTS: A direct double monoclonal sandwich enzyme-linked immunosorbent assay (ELISA) was used for the quantitative measurement of the soluble human leptin receptor. Leptin was measured by radioimmunoassay (RIA). Body composition was assessed by biphotonic absorptiometry DEXA (dual energy X-ray absorptiometry). RESULTS: We observed that the SLR is present in human plasma (range 10-100 ng/ml). SLR levels were lower in obese and overweight than lean subjects (28.7+/-8.8, 40.2+/-14.9, 51.2+/-12.5 ng/ml, respectively) and were inversely correlated to leptin and percentage of body fat (r=-0.74 and r=-0.76; respectively; P<0.0001). The ratio of circulating leptin to SLR was strongly related to the percentage of body fat (r=0.91; P<0.0001). Interestingly a gender difference was observed in SLR levels, which were higher in obese and overweight men than in obese and overweight women. In obese subjects after a 3 month low-calorie diet, SLR levels increased in proportion to the decrease in fat mass. In the gel filtration profile, SLR coeluted exactly with the bound leptin fractions. CONCLUSION: Obesity, in humans is associated with decreasing levels of the circulating soluble leptin receptor (SLR). The relationship of SLR with the degree of adiposity suggests that high SLR levels may enhance leptin action in lean subjects more than in obese subjects.

Adipose Tissue↗
PubMed2002

Allergenicity of some isoforms of white sesame proteins.

BACKGROUND: Allergy to sesame seeds is often associated with particularly severe reactions, with a high risk of anaphylaxis. The increase in reports of allergic reactions to sesame is probably due to the growing use of sesame seeds or sesame oil in food. OBJECTIVE: To determine the molecular weights of the proteins in three variety of sesame seeds and to study the isoelectric points and the allergenicity of white sesame proteins. METHODS: Extracts of white, brown and black sesame seeds were prepared. The white sesame extract, mostly used in bakery, was run on SDS-PAGE and two dimensional electrophoresis. Six sera from patients sensitized or symptomatic to sesame seed were used for Western blotting. RESULTS: The protein patterns of the white, brown and black sesame extracts showed major quantitative differences. The white extract had the higher protein concentration and contained 15 proteins of 12-79 kDa, some of them having several acidic isoelectric points. The lowest isoelectric point was 4.9 and the highest was 6.4, giving 35 isoforms. Ten of the 15 proteins (12-57.5 kDa) were recognized by specific IgE. The 12-13 kDa and 22-33 kDa proteins could correspond to the main allergens. CONCLUSION: White sesame seeds contain at least 10 allergenic proteins with acidic isoelectric points. In accordance with previous results, two of them seem to contain the major allergens.

Adolescent↗
PubMed2002

[Allergenicity of oils].

Cases of allergy to the oils of groundnut, sunflower, soya and sesame have been described in the literature. In parallel, other authors have affirmed that these oils are not allergenic. The objective of this article is to make the point on this question, to cite the procedures to which the seeds are submitted to extract the oil, to remember that the oils are not composed only of triglycerides and to describe the results of our work. Allergy of oils is a subject that is constantly submitted to controversy and the bibliography does not cease to give contradictory examples. This may be explained by the variations in extraction procedures used by the manufactures, as well as by the conditions of extraction of the proteins in the laboratory.

Allergens↗
PubMed2001

Comparative pharmacological studies of melatonin receptors: MT1, MT2 and MT3/QR2. Tissue distribution of MT3/QR2 .

The neurohormone melatonin is the central switch of the circadian rhythm and presumably exerts its activities through a series of receptors among which MT1 and MT2 have been widely studied. The third binding site of melatonin, MT3, has been recently characterized as a melatonin-sensitive form of the quinone reductase 2 (QR2, EC 1.6.99.2). In the present work, we showed that the binding of melatonin at MT3/QR2 was better described with 2-[125I]-iodomethoxy-carbonylamino-N-acetyltryptamine (2-[125I]-I-MCA-NAT) and, most importantly, that it was measurable at 20 degrees while it has been initially described and thoroughly studied using 2-[125I]-iodomelatonin at 4 degrees. Under these novel conditions, binding to MT3 could be traced without cross-reactivity with MT1 and MT2 receptors and, moreover, under conditions similar to those used to measure MT3/QR2 catalytic activity. The pharmacology established here on hamster kidney samples using the reference compounds remained essentially as already described using other experimental conditions. A new series of compounds with nanomolar affinity for the MT3 binding site and a high MT3 selectivity versus MT1 and MT2 is reported. In addition, we further document the MT3/QR2 binding site by demonstrating that it was widely distributed among mammals, although inter-species and inter-tissues differences exist. The present report details new experimental conditions for the pharmacological study of melatonin-sensitive QR2 isoforms, and suggests that, in addition to an already demonstrated inter-species difference, inter-tissues differences in QR2 sensitivity to melatonin may exist in primates and, therefore, represent an original and interesting route of investigation on the effect of melatonin on MT3/QR2.

Animals↗
PubMed2001

Detection of moderate hyperhomocysteinemia: comparison of the Abbott fluorescence polarization immunoassay with the Bio-Rad and SBD-F high-performance liquid chromatographic assays.

The importance of accurate methods for homocysteine measurement has been emphasized. We compared the results obtained with the most commonly used high-performance liquid chromatography (HPLC) assay, and two recently commercially available methods: another HPLC and a fluorescence polarization immunoassay, in plasmas from normo- or hyperhomocysteinemic patients. A significant agreement between the different methods in classifying the results as hyper or normal-homocysteinemia was observed. However, a significant difference between the results was found. Standardization is urgently necessary to improve the concordance of homocysteine determination.

Chemistry, Clinical↗
PubMed2001

The cholesterol-lowering property of soybeans fed to rats is related to the fasting duration.

Numerous factors affect plasma cholesterol and, therefore, represent potential interferences with the specific effects of diet on lipid metabolism. After casein intake, serum cholesterol levels depend on many experimental conditions in rats, such as the type of casein, the presence or absence of cholesterol in the diet, the age and strain of rat, the diet composition, the nutritional status. The effect of fasting duration on selected parameters was studied in adult male Wistar rats fed a 20% casein and 1% cholesterol-based diet. No changes were observed in total serum, lipoproteins-B and HDL cholesterol and in triglyceride values after an 8 h-fast compared to non-fasted animals. A significant decrease was induced in total and lipoproteins-B cholesterol with a 12 h-fast. A prolonged fast resulted in a significant decrease in these parameters and in triglycerides and in HDL-cholesterol levels. Fasted animals fed heated soybean meal instead of casein did not display a marked decrease in serum lipids. It appeared that the fasting effect was more marked in animals fed casein than in animals fed soybeans. These results showed the importance of experimental conditions such as nutritional status of animals when blood samples are taken in studies of the hypocholesterolemic effect of soy protein compared to casein.

Animals↗
PubMed2001

Parallel synthesis and pharmacological screening of nonpeptide ligands of the neuropeptide Y receptor subtype Y5.

Several series of low-molecular-mass ligands of the neuropeptide receptor subtype Y5 were prepared using a mixed strategy of synthesis on solid phase and in solution. Collections of single compounds were obtained by an automated parallel procedure which allowed quick variation and investigation of the central spacer moiety, as well as of the aromatic substituents on each side. The strategy of parallel synthesis and screening of partially purified analogs helped to select rapidly potent and selective leads which displayed comparable antagonistic potency against neuropeptide Y activity on the Y5 receptor and better receptor selectivity than the original reference compounds.

Animals↗
PubMed2001

Antiparkinsonian agent piribedil displays antagonist properties at native, rat, and cloned, human alpha(2)-adrenoceptors: cellular and functional characterization.

Compared with cloned, human (h)D(2) receptors (pK(i) = 6.9), the antiparkinsonian agent piribedil showed comparable affinity for halpha(2A)- (7.1) and halpha(2C)- (7.2) adrenoceptors (ARs), whereas its affinity for halpha(2B)-ARs was less marked (6.5). At halpha(2A)- and halpha(2C)-ARs, piribedil antagonized induction of [(35)S]guanosine-5'-O-(3-thio)triphosphate (GTPgammaS) binding by norepinephrine (NE) with pK(b) values of 6.5 and 6.9, respectively. Furthermore, Schild analysis of the actions of piribedil at halpha(2A)-ARs indicated competitive antagonism, yielding a pA(2) of 6.5. At a porcine alpha(2A)-AR-Gi1alpha-Cys351C (wild-type) fusion protein, piribedil competitively abolished (pA(2) = 6.5) GTPase activity induced by epinephrine. However, at a alpha(2A)-AR-Gi1alpha-Cys351I (mutant) fusion protein of amplified sensitivity, although still acting as a competitive antagonist (pA(2) = 6.2) of epinephrine, piribedil itself manifested weak partial agonist properties. Similarly, piribedil weakly induced mitogen-activated protein kinase phosphorylation via wild-type halpha(2A)-ARs, although attenuating its phosphorylation by NE. As demonstrated by functional [(35)S]GTPgammaS autoradiography in rats, piribedil antagonized activation by NE of alpha(2)-ARs in cortex, amygdala, and septum. Antagonist properties were also expressed in a dose-dependent enhancement of the firing rate of adrenergic neurons in locus ceruleus (0.125-4.0 mg/kg i.v.). Furthermore, piribedil (2.5-4.0 mg/kg s.c.) accelerated hippocampal NE synthesis, elevated dialysis levels of NE in hippocampus and frontal cortex, and blocked hypnotic-sedative properties of the alpha(2)-AR agonist xylazine. Finally, piribedil showed only modest affinity for rat alpha(1)-ARs (5.9) and weakly antagonized NE-induced activation of phospholipase C via halpha(1A)-ARs (pK(b) = 5.6). In conclusion, piribedil displays essentially antagonist properties at cloned, human and cerebral, rat alpha(2)-ARs. Blockade of alpha(2)-ARs may, thus, contribute to its clinical antiparkinsonian profile.

Adrenergic alpha-1 Receptor Antagonists↗
PubMed2000

Synthesis of phenalene and acenaphthene derivatives as new conformationally restricted ligands for melatonin receptors.

Conformationally restricted phenalene and acenaphthene derivatives 5 were synthesized from phenalen-1-one and acenaphthen-1-one derivatives using the Horner-Emmons reaction. The amines were prepared through the corresponding isocyanates by the Curtius reaction on the acids or by the reduction of the nitriles. Amido derivatives (R(3) = Me, Et, n-Pr, c-Pr) were prepared by acylation of the amines with the appropriate anhydrides or acid chlorides or by the reductive acylation of the nitriles. The affinities of the compounds for melatonin binding sites were evaluated in vitro in binding assays using chicken brain melatonin and the human mt(1) and MT(2) receptors expressed in HEK-293 cells. The functionality of the compounds was determined by the potency to lighten the skin of Xenopus laevis tadpoles. Highly potent compounds were obtained. The data highlighted the role of the methoxy group located in the ortho position to the ethylamido chain as compounds with picomolar affinities such as 14c were obtained (chicken brain, hmt(1), hMT(2) K(i) values = 0.02, 0.008, 0.069 nM, respectively). Compound 14c was equipotent to the corresponding dimethoxy derivative 15c (chicken brain, hmt(1), hMT(2) K(i) values = 0.07, 0.016, 0.1 nM, respectively). On the other hand, the restricted conformation of the amido chain did not influence selectivity for the cloned hmt(1) and hMT(2) receptors. These compounds were also potent agonists of melanophore aggregation in X. laevis. 15a,c were several hundred fold more potent than melatonin (EC(50) = 0.025, 0.004 nM, respectively). Conformational studies indicated that the minimum energy folded conformation of the ethylamido chain could constitute the putative active form in the receptor site in agreement with previous results.

Acenaphthenes↗
PubMed2000

Inhibition of vitamin B12 metabolism by OH-cobalamin c-lactam in rat oligodendrocytes in culture: a model for studying neuropathy due to vitamin B12 deficiency.

Vitamin B12 is implicated in methylation processes. Myelin basic protein is methylated on one arginine group. A defect in methylation could produce an unstable protein, leading to neurological disorders. In order to study myelin basic protein, we have developed the cultures of newborn rat oligodendrocytes in vitamin B12-depleted medium. As these cells do not grow without serum, vitamin B12 is always present. We overcame this problem by using OH-cobalamin c-lactam, an antagonist of B12. To ensure that the system was vitamin B12 deficient, we measured the concentrations of homocysteine and methylmalonic acid whose accumulations reflect a vitamin B12 deficiency. Methylmalonic acid was measured by mass spectrometry and homocysteine by HPLC. We obtained a powerful model for studying the influence of B12 deficiency on the synthesis of myelin compounds.

Animals↗
PubMed2000

Serotonin(2C) receptors tonically suppress the activity of mesocortical dopaminergic and adrenergic, but not serotonergic, pathways: a combined dialysis and electrophysiological analysis in the rat.

The present study evaluated, via a combined electrophysiological and dialysis approach, the potential influence of serotonin (5-HT)(2C) as compared to 5-HT(2A) and 5-HT(2B) receptors on dopaminergic, adrenergic, and serotonergic transmission in frontal cortex (FCX). Whereas the selective 5-HT(2A) antagonist MDL100,907 failed to modify extracellular levels of dopamine (DA), noradrenaline (NA) or 5-HT simultaneously quantified in single dialysate samples of freely-moving rats, the 5-HT(2B)/5-HT(2C) antagonist SB206,553 dose-dependently increased levels of DA and NA without affecting those of 5-HT. This action was attributable to 5-HT(2C) receptor blockade inasmuch as the selective 5-HT(2C) antagonist SB242,084 likewise increased FCX levels of DA and NA, whereas the selective 5-HT(2B) antagonist SB204,741 was ineffective. Further, the preferential 5-HT(2C) receptor agonist Ro60-0175 dose-dependently depressed FCX levels of DA. The suppressive influence of 5-HT(2C) receptors on DA release was also expressed on mesolimbic and nigrostriatal dopaminergic pathways, in that levels of DA in nucleus accumbens and striatum were likewise reduced by Ro60-0175 and elevated, though less markedly, by SB206,553. In line with the above findings, Ro60-0175 dose-dependently decreased the firing rate of ventrotegmental dopaminergic and locus coeruleus (LC) adrenergic perikarya, whereas their activity was dose-dependently enhanced by SB206,553. Furthermore, SB206,553 transformed the firing pattern of ventrotegmental dopaminergic neurons into a burst mode. In contrast to SB206,553, MDL100,907 had little affect on the firing rate of dopaminergic or adrenergic neurons. In conclusion, as compared to 5-HT(2A) and 5-HT(2B) receptors, 5-HT(2C) receptors exert a tonic, suppressive influence on the activity of mesocortical - as well as mesolimbic and nigrostriatal - dopaminergic pathways, likely via indirect actions expressed at the level of their cell bodies. Frontocortical adrenergic, but not serotonergic, transmission is also tonically suppressed by 5-HT(2C) receptors.

Animals↗
PubMed2000

Hydrolysis of phospholipids by purified milk lipoprotein lipase. Effect of apoprotein CII, CIII, A and E, and synthetic fragments.

Different pyrene-labeled phospholipid monolayer vesicles were used as substrates for the bovine milk lipoprotein lipase activity. The effects of synthetic fragments of apoprotein C II were measured on the hydrolysis of 1-myristoyl-2[9(1pyrenyl)-nonanoyl] phosphatidylcholine in vesicles: The activating capacity of fragments 30-78 and 43-78, 50-78 and 55-78, compared to entire apo CII, were similar to that obtained with hydrolysable triglycerides. Our study shows that the longer the carboxy terminal fragment is, the higher is the activation. The phospholipid hydrolysis activity represents in the presence of apo C II, 36% of the triglycerides hydrolysis activity. Phospholipid hydrolysis is less dependent on activator than triglycerides hydrolysis (100% and 300% of increase with apo CII for phosphatidyl-choline and triglycerides respectively). The ratio hydrolysis without apo C II/hydrolysis with apo CII was different when other phospholipids than myrystoyl-phospatidylcholine were assayed: phosphatidyl-serine, ethanolamine, -choline, -glycerol, or diglycerides and butanoylglycerols. Fragment CIII(1) (1-40) which did not bind to lipids, had no inhibitory effect. The entire sugar moiety and the first 40 amino acids are not required for the total inhibition of LPL. Inhibition was also obtained with Apo A I, A II,C I and fragments of apo E.

Animals↗