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E Samain

Publications and source records attributed to E Samain.

At least 37 records · Page 2Linked to original sources
PubMed1999

Production of O-acetylated and sulfated chitooligosaccharides by recombinant Escherichia coli strains harboring different combinations of nod genes.

High cell density cultivation of recombinant Escherichia coli strains harboring the nodBC genes (encoding chitooligosaccharide synthase and chitooligosaccharide N-deacetylase, respectively) from Azorhizobium caulinodans has been previously described as a practical method for the preparation of gram-scale quantities of penta-N-acetyl-chitopentaose and tetra-N-acetylchitopentaose (Samain, E., Drouillard, S., Heyraud, A., Driguez, H., Geremia, R.A., 1997. Carbohydr. Res. 30, 235-242). We have now extended this method to the production of sulfated and O-acetylated derivatives of these two compounds by coexpressing nodC or nodBC with nodH and/or nodL that encode chitooligosaccharide sulfotransferase and chitooligosaccharide O-acetyltransferase, respectively. In addition, these substituted chitooligosaccharides were also obtained as tetramers by using nodC from Rhizobium meliloti instead of nodC from A. caulinodans. These compounds should be useful precursors for the preparation of Nod factor analogues by chemical modification.

Acetylation↗
PubMed1999

Ligand specificity of a high-affinity binding site for lipo-chitooligosaccharidic Nod factors in Medicago cell suspension cultures.

Rhizobial lipo-chitooligosaccharides (LCOs) are signaling molecules involved in host-range recognition for the establishment of the symbiosis with leguminous plants. The major LCO of Rhizobium meliloti, the symbiont of Medicago plants contains four or five N-acetylglucosamines, O-acetylated and N-acylated with a C16:2 fatty acid on the terminal nonreducing sugar and O-sulfated on the reducing sugar. In this paper, the ligand specificity of a high-affinity binding site (Nod factor binding site 2 or NFBS2), enriched in a plasma membrane-enriched fraction of Medicago cell suspension cultures, is reported. By using chemically synthesized LCOs, the role of structural elements, important for symbiotic activities, as recognition motifs for NFBS2 was determined. The results show that the substitutions on the nonreducing sugar of the LCOs (the O-acetate group, the fatty acid, and the hydroxyl group on the C4 of the sugar) are determinants for high-affinity binding to NFBS2. In contrast, the sulfate group, which is necessary for all biological activities on Medicago, is not discriminated by NFBS2. However, the reducing sugar of the LCO seems to interact with NFBS2, because ligand binding is affected by the reduction of the free anomeric carbon and depends on the number of N-acetyl glucosamine residues. These results suggest that the recognition of the LCOs by NFBS2 is mediated by structural elements in both the lipid and oligosaccharidic moities, but not by the sulfate group.

Journal Article↗
PubMed1999

The living factory: in vivo production of N-acetyllactosamine containing carbohydrates in E. coli.

Scientific and commercial interest in oligosaccharides is increasing, but their availability is limited as production relies on chemical or chemo-enzymatic synthesis. In search for a more economical, alternative procedure, we have investigated the possibility of producing specific oligosaccharides in E. coli that express the appropriate glycosyltransferases. The Azorhizobium chitin pentaose synthase NodC (a beta(1,4)GlcNAc-oligosaccharide synthase), and the Neisseria beta(1,4)galactosyltransferase LgtB, were co-expressed in E. coli. The major oligosaccharide isolated from the recombinant strain, was subjected to LC-MS, FAB-MS and NMR analysis, and identified as betaGal(1,4)[betaGlcNAc(1,4)]4GlcNAc. High cell density culture yielded more than 1.0 gr of the hexasaccharide per liter of culture. The compound was found to be an acceptor in vitro for betaGal(1,4)GlcNAc alpha(1,3)galactosyltransferase, which suggests that the expression of additional glycosyltransferases in E. coli will allow the production of more complex oligosaccharides.

Amino Sugars↗
PubMed1999

Placebo-controlled study of inhaled nitric oxide to treat hypoxaemia during one-lung ventilation.

The aim of this prospective, placebo-controlled study was to assess if unilaterally inhaled nitric oxide 20 ppm could treat hypoxaemia during one-lung ventilation. Sixty patients undergoing pulmonary resection using a lateral thoracotomy were allocated randomly to a control or nitric oxide group (NO group). During one-lung ventilation in the lateral decubitus position, the lungs were ventilated mechanically with 90% oxygen--10% nitrogen. After randomization, if PaO2 decreased to less than 9.3 kPa during one-lung ventilation, nitric oxide 20 ppm or nitrogen was added to the inspired gas. The criterion for treatment efficacy was an increase in PaO2 to greater than 9.3 kPa after gas administration. Eight patients in the control group and eight in group NO experienced hypoxaemia during one-lung ventilation. PaO2 was not significantly different in the two groups at the time of gas administration (control group mean 8.0 (SD 0.6) kPa; NO group 8.5 (0.5) kPa). The efficacy criterion was reached in two of eight patients in the control and NO groups. The results of this study showed that inhaled nitric oxide 20 ppm, administered in the dependent lung, was not superior to nitrogen in the treatment of hypoxaemia during one-lung ventilation. Nitric oxide should not be recommended as an alternative to conventional management of hypoxaemia in this condition.

Adult↗
PubMed1999

Dual effect of cicletanine on the Na+-H+ exchanger in chick embryonic cardiomyocytes.

Na+-H+ exchanger is thought to play an important role in the regulation of the intracellular pH (pHi) and in the cardiac cell injury induced by ischemia and reperfusion. The aim of this study was to assess the effect of cicletanine, an antihypertensive compound in humans, which has been reported to have cardioprotective effect under an ischemia-reperfusion process, on Na+-H+ exchanger activity in ventricular cardiomyocytes isolated from chick embryo. Na+-H+ exchanger activity was assessed by the rate of pHi recovery after an acid load. A dual effect was observed: at low concentration of cicletanine (10(-7) M), Na+-H+ exchanger activity was significantly decreased, whereas at higher concentrations (10(-6)-10(-5) M), a significant stimulation of the exchanger was observed. These results suggest that cicletanine modulates pHi recovery in cardiac cells after cellular acid load.

Animals↗
PubMed1999

ANG II-induced Ca(2+) increase in smooth muscle cells from SHR is regulated by actin and microtubule networks.

We hypothesized that the cytoskeletal network in vascular smooth muscle cells (VSMC) is critical to the signaling pathways from angiotensin (ANG) II-receptor subtype 1 (AT(1)) activation to intracellular Ca(2+) (Ca(2+)(i)) release from internal stores and Ca(2+) influx. This was tested in spontaneously hypertensive rats (SHR), in which differences were reported in cultured aortic VSMC Ca(2+)(i) regulation and G protein function compared with those in normotensive Wistar-Kyoto (WKY) rats. In cultured aortic VSMC, disorganization of actin filaments with cytochalasin D (2 micromol/l) decreased the ANG II-induced Ca(2+)(i) release from internal stores and the ANG II-induced Ca(2+) influx in SHR in a reversible fashion, whereas it was without effect in WKY rats. On the other hand, blocking the dynamic state of the microtubule network significantly reduced ANG II-induced Ca(2+)(i) release from internal stores but was without effect on Ca(2+) influx in either SHR or WKY rats. This study demonstrates for the first time that, in the SHR, actin filaments play a major role in linking AT(1)-receptor activation to both Ca(2+)(i) release mechanisms and capacitative Ca(2+) influx. Furthermore, a functionally intact microtubule system is a necessary prerequisite for ANG II-induced Ca(2+)(i) release in both strains.

Actins↗
PubMed1999

[Cellular adhesion to elements of the extracellular matrix in the hypertensive rat modulates the effect of angiotensin II].

This study was to assess the role of different components of the extracellular matrix (ECM) on the mobilization of Cai++ induced by angiotensin II in vascular smooth muscle cells (VSMC) from hypertensive (SHR) and normotensive (WKY) rats. The effect of AII (10-6 M) on Cai++ release was studied in VSMC isolated from the aorta of 5-week-old WKY and SHR using fluorescent imaging microscopy (fura-2). Cai++ mobilization was characterized by amplitude, slope of Cai++ increase and total amount of Cai++. Cells were cultured on glass coverslips (control) or coated with either collagen I, collagen IV, vitronectin, fibronectin and extracellular matrix (ECM) and studied at confluence between passage 3 and 9. A significant increase of Cai++ released by AII has been observed with cells from WKY cultured on collagen I (meam +/- SEM, amplitude: 192 +/- 12% of control values, slope: 194 +/- 13%, total amount Cai++: 173 +/- 12%, n = 270, p < or = 0.0001 for each, unpaired t-test). Conversely, response with SHR was not significatively modified. Cai++ mobilization was not significatively modified after culture of VSMC from SHR and WKY on collagen IV. A significative decrease of the slope (WKY: 66 +/- 6%, p < or = 0.0001; SHR: 83 +/- 5%, p < or = 0.03) and of the amount of Cai++ (WKY: 74 +/- 7%, p < or = 0.01; SHR: 74 +/- 5%, p < or = 0.01) has been observed after culture of VSMC from the 2 strains on vitronectin. A decrease in amplitude (53 +/- 3%, p < or = 0.0001), slope (38 +/- 4%, p < or = 0.0001) and Cai++ release (69 +/- 5%, p < or = 0.004, n = 106) has been observed in VSMC from SHR seeded on fibronectin. Conversely, in VSMC from WKY, Cai++ mobilisation has not been modified compared with control cells. Culture of VSMC from SHR on ECM induced a significative decrease of amplitude (49 +/- 2%), slope (54 +/- 4%) and Cai++ release (53 +/- 3%, p < or = 0.0001 for each, n = 122), while in WKY, ECM induced a significative stimulation of these parameters (amplitude: 157 +/- 11%, slope: 149 +/- 13% and Cai++ release: 130 +/- 9%, p < or = 0.0001 for each, n = 247). These results show that the Cai++ mobilization induced by AII is modified by the adhesion of cells to different ECM components. This suggests a modulation of the A II-associated signalling events via the focal adhesion points. Furthermore, a difference in this modulation is observed between SHR and WKY when cells are seeded on collagen I, fibronectin or ECM. These modulations of Cai++ mobilization could play a role in the regulation of growth and differentiation of cells during the development of hypertension.

Angiotensin II↗
PubMed1999

[How to handle cardiovascular treatments during general anesthesia?].

The risk of interference with anaesthesia and the risk of decompensation of the disease must be considered for each drug. Beta-blockers reduce the body's capacity to react to hypovolaemia, but they are beneficial by limiting the response to nociceptive stimuli and by reducing the incidence of myocardial ischaemia. Treatment should therefore be continued. Interferences with the dihydropyridine class of calcium channel blockers on peripheral vasomotor activity are moderate and additive. These agents are well tolerated and can be continued until the operation. Verapamil and diltiazem have a chronotropic and negative inotropic effect which is additive with that of anaesthetics. Administration of these drugs before the operation does not raise any major problems, nor does their discontinuation. Angiotensin-converting enzyme (ACE) inhibitors, used in hypertension and heart failure, considerably reduce the tolerance of factors modifying the blood pressure equilibrium, especially hypovolaemia or haemorrhage. In practice, ACE inhibitors carry a risk of intraoperative hypotension, requiring the use of vasopressor amines to maintain blood pressure. Continuation of treatment has only minimal advantages, regardless of the indication and there is no risk of rebound effect after stopping treatment. The treatment washout period depends on the duration of action of the product. However, discontinuation of treatment is never imperative, regardless of the context.

Adrenergic beta-Antagonists↗
PubMed1998

[Areactive unilateral mydriasis after diagnostic celioscopy under general anesthesia].

A unilateral areactive mydriasis occurred in a 49-year-old ASA I woman after a coelioscopic procedure while anaesthesia was maintained for an associated procedure. The various causes of brain stem damage were considered. The inability to perform a complete neurologic assessment resulted in the indication of a cerebral computerised tomography (CT) scan. The diagnosis of Adie's tonic pupil was made a posteriori, taking into consideration: 1) complete recovery without neurologic deficit; 2) unremarkable CT scan; 3) previous transient episodes of unilateral areactive mydriasis.

Anesthesia, General↗
PubMed1998

[Cardiovascular effects of anesthesia. Management of cardiovascular therapy during the perioperative period].

General anesthesia changes circulatory haemodynamics in three ways: a decrease in sympathetic tone, a decrease in VO2, and a change in baroreceptor reflex function. These effects may have important consequences in patients with cardiovascular disease whose stability depends on these different factors. In addition, the anaesthesia should be adapted to the intensity of the surgical stimuli which tend to increase sympathetic activity, produce tachycardia and increase the blood pressure which may cause decompensation of some cardiac diseases (coronary artery disease for example). Drugs used in the treatment of cardiac disease may interfere with anaesthesia but they are usually continued in order to operate patients under stable cardiovascular conditions.

Anesthesia, General↗
PubMed1997

High level production of a cellulase-free xylanase in glucose-limited fed batch cultures of a thermophilic Bacillus strain.

Bacillus sp. strain XE and its mutant derivative strain D3 produce a thermostable xylanase which is suitable for enzymatic bleaching of kraft pulp. Xylanase synthesis was shown to be induced by the soluble products of xylan hydrolysis (xylooligosaccharide) and equally, catabolically-repressed when these oligosaccharides accumulate in the medium. An optimal balance between these two antagonistic effects was obtained in a carbon-limited, fed-batch culture with continuous xylooligosaccharide feeding. To reduce substrate cost, the xylooligosaccharide could be 90% substituted by glucose without reduction of the xylanase production rate. Xylanase production ceased when the activity reached approximately 380 U ml-1 due to an amino acid shortage. A continuous supply of exogenous amino acids allowed the production to continue to more than 1000 U ml-1.

Amino Acids↗
PubMed1997

Gram-scale synthesis of recombinant chitooligosaccharides in Escherichia coli.

Cultivation of Escherichia coli harbouring heterologous genes of oligosaccharide synthesis is presented as a new method for preparing large quantities of high-value oligosaccharides. To test the feasibility of this method, we successfully produced in high yield (up to 2.5 g/L) penta-N-acetyl-chitopentaose (1) and its deacetylated derivative tetra-N-acetyl-chitopentaose (2) by cultivating at high density cells of E. coli expressing nodC or nodBC genes (nodC and nodB encode for chitooligosaccharide synthase and chitooligosaccharide N-deacetylase, respectively). These two products were easily purified by charcoal adsorption and ion-exchange chromatography. One important application of compound 2 could be its utilisation as a precursor for the preparation of synthetic nodulation factors by chemical acylation.

Acetylation↗
PubMed1996

Design and chemoenzymatic synthesis of thiooligosaccharide inhibitors of 1,3:1,4-beta-D-glucanases.

A successful chemoenzymatic synthesis of oligosaccharides with an interglucosidic sulfur atom as inhibitors of 1,3:1,4-D-glucanases is described. The key compound 3a was synthesized from acetylated 1-thio-beta-laminaribiose 4 and the methyl 4'-O-triflyl-lactoside 5. After de-O-acylation, the tetrasaccharide 3b was used as an acceptor and glucose-1-P as a donor in a phosphorolytic elongation catalysed by cellodextrin phosphorylase from Clostridium thermocellum. The expected pentasaccharide 2a and hexasaccharide 1 were isolated in 56% and 13% yield, respectively. As expected, the thiooligosaccharides 1, 2a, and 3b were resistant to enzymatic cleavage by 1,3:1,4-beta-D-glucanase isolated from Bacillus licheniformis. Furthermore, they have been shown to act as competitive inhibitors of the hydrolysis of the chromophoric trisaccharide substrate 11 by this enzyme.

Binding Sites↗
PubMed1995

Sucrose analogues modified at position 3: chemoenzymatic synthesis and inhibition studies of dextransucrases.

Conditions for the large-scale (molar) oxidation of sucrose by Agrobacterium tumefaciens were improved, thus leading to homogeneous solutions of 3-ketosucrose in 40% yield. Treatment of this solution with hydroxylamine or methoxylamine afforded the corresponding oximes 3a and 3b (isolated as acetates) in excellent yield. Dissolving-metal reduction of these oximes gave mixtures of amino disaccharides in which the gluco epimer (3-amino-3-deoxysucrose) was predominant. A more efficient approach to this amino sucrose was provided by the highly stereoselective hydrogenation of 3-ketosucrose peracetate (7), which gave exclusively the allo isomer 8 (2,4,6-tri-O-acetyl-alpha-D-allopyranosyl 1,3,4,6-tetra-O-acetyl-beta-D-fructofuranoside). Upon reaction with lithium azide, the triflate derived from 8, compound 9, afforded 3-azido-3-deoxysucrose peracetate (10) which was converted into 3-amino-3-deoxysucrose (12). The reaction of triflate 9 with potassium ethylxanthate led to a mixture of products (the expected 3-S-ethoxythiocarbonyl-3-thiosucrose derivative and the peracetates of 3-thiosucrose and of 3-thiosucrose disulfide), which could be all converted into 3-thiosucrose (17). Sucrose analogues 12 and 17 were not substrates of dextransucrases from various strains of L. mesenteroides, nor did they participate in glycosyl transfer reactions to an acceptor (maltose). Compounds 3a and 12 were found to be strong competitive inhibitors of the dextran synthesis process (dextransucrase from strain B-1397). These results indicate that 3a and 12 compete effectively with sucrose for the sucrose binding site but are unable to participate as glycosyl donors in the polymerization or glycosyl-transfer processes.

Agrobacterium tumefaciens↗
PubMed1994

[Use of Diprivan in cardioversion and interventional cardiology].

Propofol ensures a calm and rapid induction of anaesthesia in case of planned cardioversion for supraventricular arrhythmia. An appropriate level of anaesthesia is obtained with a dose of 1.4 to 2 mg.kg-1. Propofol does not affect the success rate of cardioversion. However, given as a bolus injection, it causes a more pronounced decrease in blood pressure than other induction agents and the rate of apnoea is higher. The incidence of these adverse effects may be reduced by slowly titrating the dose. The frequent association with cardiac disease, in particular valvular disease or coronary insufficiency, should be taken into account and may represent a contra-indication for the administration of propofol. Furthermore, administration of this agent is not indicated if the arrhythmia is poorly tolerated, because of the risk of increasing hypotension. The known advantages of propofol on recovery have no significant role in this indication.

Anesthesia, Intravenous↗
PubMed1992

Clostridium neopropionicum sp. nov., a strict anaerobic bacterium fermenting ethanol to propionate through acrylate pathway.

Strain X4 was isolated several years ago from an anaerobic mesophilic plant treating vegetable cannery waste waters. It was the first example of propionic fermentation from ethanol. Morphologic and physiologic characterizations of the strain are presented here. This strain is described as type strain of a new species, Clostridium neopropionicum sp. nov. Whole cells of strain X4 ferment [1-13C] ethanol and CO2 to [2-13C] propionate, [1-13C] acetate and [2-13C] propanol, suggesting the absence of a randomizing pathway during the propionate formation. Enzymes involved in this fermentation were assayed in cell-free extracts of cells grown with ethanol as sole substrate. Alcohol dehydrogenase, aldehyde dehydrogenase, phosphate acetyl transferase, acetate kinase, pyruvate synthase, lactate dehydrogenases, and the enzymes of the acrylate pathway were detected at activities sufficient to be involved in ethanol fermentation. The same pathway may be used for the degradation of lactate or acrylate to acetate.

Acrylates↗