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Biomedical subjects

M Lenfant

Publications and source records attributed to M Lenfant.

At least 37 records · Page 2Linked to original sources
PubMed1990

Synthesis and activity of NAcSerAspLysPro analogues on cellular interactions between T-cell and erythrocytes in rosette formation.

Analogues of NAcSerAspLysPro (AcSDKP), a natural regulator of hematopoiesis isolated from fetal calf bone marrow, were synthesized. The biological activity of these molecules were evaluated in vitro in the rosette assay, which measures the interaction between human Jurkat T-cells and sheep red blood cells. In this test, the tripeptide SerAspLys was the most efficient. Inhibitory activity was detected at the concentration 10(-14) M for the analogue and at 10(-9) M for the parent tetrapeptide. The dipeptide NAcSerAsp still showed activity but at much higher doses (10(-6) M). Substitution of polar amino acids led mostly to inactive molecules. Thus, replacement of Ser by Ala, or Lys by Orn yielded completely inactive compounds and replacement of Asp by Glu decreased the activity (10(-6) M). The present study gives an insight into the role of individual amino acids of AcSDKP in the inhibition of the rosette formation which implicates interactions with T-cell CD2 glycoprotein.

Amino Acid Sequence↗
PubMed1990

In vivo effect of the tetrapeptide, N-acetyl-Ser-Asp-Lys-Pro, on the G1-S transition of rat hepatocytes.

The synthetic molecule N-Acetyl-Ser-Asp-Lys-Pro (Ac-SDKP), corresponding to the low molecular weight inhibitory factor preventing in vivo haematopoietic stem cell (CFU-S) entry into DNA synthesis, was tested in two heterologous systems in vivo: adult regenerating rat liver and 10-day-old rat hepatocytes synchronized by an irritating trigger. In both systems, it was shown that doses of 2-8 micrograms kg-1 of tetrapeptide inhibited 50-70% of the hepatocyte G1-S transitions.

Animals↗
PubMed1990

Formation of glyceryl 2-mononitrate by regioselective bioconversion of glyceryl trinitrate: efficiency of the filamentous fungus Phanerochaete chrysosporium.

Various microorganisms have been evaluated for their ability to hydrolyze glyceryl trinitrate (GTN) to glyceryl dinitrates and mononitrates. Provided that the GTN extracellular concentration was under the lethal dose, metabolite formation and regioselectivity depend on the nature of the strain used. In particular, Phanerochaete chrysosporium at a sublethal dose (3 mM) converts GTN into 1,2-glyceryl dinitrate and 2-glyceryl mononitrate (2-GMN) with a 80% regioselectivity in both steps. This bioconversion, when carried out in fermentors at 28 degrees C, allowed formation of 2-GMN at a rate of 12 mumol/h/g of dried mycelium. Successive batches of 3 mM GTN could be converted into 2-GMN as long as consecutive additions of glycerol or glucose were effected to ensure cell survival and the efficiency of the enzymatic system involved.

Basidiomycota↗
PubMed1989

Nitric oxide formation during microsomal hepatic denitration of glyceryl trinitrate: involvement of cytochrome P-450.

Glyceryl trinitrate was denitrated by rat liver microsomes in the presence of NADPH with formation of a mixture of glyceryl dinitrates and glyceryl mononitrates. The highest activity was obtained under anaerobic conditions and the reaction was inhibited by O2 indicating that it is a reductive denitration. It was also inhibited by CO, metyrapone and miconazole showing that it was catalyzed by cytochrome P-450. Finally the formation of the cytochrome P-450-Fe(II)-NO complex during this reaction was shown by visible spectroscopy. These data demonstrate that microsomal reductive denitration of glyceryl trinitrate is catalyzed by cytochrome P-450 and can be involved in the formation of the endothelium-derived relaxing factor (EDRF = nitric oxide).

Animals↗
PubMed1989

Suppression of mast cell colony formation by a low molecular weight fraction of fetal calf bone marrow extract.

A semi-purified fraction extracted from fetal calf bone marrow was previously shown to contain a tetrapeptide N-Ac-Ser-Asp-Lys-Pro which inhibits in mice, hematopoietic stem cell entry into the cell cycle. This peptide however, did not exhibit any effect on either IL-3 nor GM-CSF dependent cell growth. We report herein that a semi-purified fraction also contains another activity which is antagonistic to IL-3. Addition of the fraction in vitro decreased IL-3 dependent mast cell colony formation. Growth of IL-3 dependent cell lines (DA-1 and FDC-P2) was also suppressed. No effect was observed in the same dose range on granulocyte-macrophage colony formation nor on IL-3 independent cell growth.

Animals↗
PubMed1989

Bioconversion of glyceryl trinitrate into mononitrates by Geotrichum candidum.

Glyceryl trinitrate (GTN) 2 mM was quantitatively converted into its 1 and 2 mononitrate derivatives by Geotrichum candidum, with consumption of the nitrite ions produced. The conversion proceeded at a rate independent of the addition of either organic carbon or organic nitrogen sources. Eight batches of nitrate ester, which were added every 24 hours, were successfully converted as far as during the bioconversion process GTN concentration did not exceed 2 mM. When those limiting conditions were not observed, dramatic toxicity of GTN was noticed.

Biodegradation, Environmental↗
PubMed1989

Inhibitor of hematopoietic pluripotent stem cell proliferation: purification and determination of its structure.

We report here a five-step purification procedure that led to the isolation from fetal calf bone marrow extract of a tetrapeptide, Ac-Ser-Asp-Lys-Pro (Mr 487), exerting a high inhibitory activity on the proliferation of hematopoietic pluripotent stem cells [defined here as spleen colony-forming units (CFU-S)]. The structure of this molecule was established from amino acid analysis, fast atom bombardment mass spectrometry, and 1H nuclear magnetic resonance spectral data. This structure was confirmed by comparison with the corresponding synthetic molecule, which presents identical physiochemical characteristics and biological properties. Natural and synthetic peptides administered to mice (at a dose of 100 ng per mouse) after one injection of cytosine arabinonucleoside prevent CFU-S recruitment into DNA synthesis.

Animals↗
PubMed1989

Enhancement of the adherence of hematopoietic stem cells to mouse bone marrow-derived stromal cell line MS-1-T by a tetrapeptide acetyl-N-Ser-Asp-Lys-Pro.

The tetrapeptide acetyl-N-Ser-Asp-Lys-Pro (AcSDKP) has been shown to inhibit in vivo the hematopoietic stem cell (spleen colony-forming unit; CFU-S) entry into cell cycle in cytosine arabinoside-treated mice. Our data showed that AcSDKP has no effect on interleukin 3 (IL-3)-dependent DA-1 cell proliferation or on granulocyte-macrophage colony-forming cell and mast cell colony formation, whereas it enhances the adherence of CFU-S to the bone marrow-derived hematopoietic supportive stromal cell line MS-1-T. AcSDKP suppresses MS-1-T proliferation but does not modify granulocyte-macrophage colony-stimulating activity secretion by these cells. This suggests that the peptide does not counteract the activity of the IL-3 receptor on CFU-S but acts on MS-1-T and in particular at the level of CFU-S/MS-1-T interactions.

Animals↗
PubMed1988

Ca2+-channel blockers modulate the oxidative burst induced with arachidonic acid in macrophage-like P 388D1 cells. Interaction with peripheral benzodiazepines.

Ca2+-channel blockers are shown to modulate, like peripheral benzodiazepines, the oxidative burst induced by arachidonic acid in the macrophage-like P 388D1 cell line. Nifedipine (1 and 10 nM) enhanced the cellular response to arachidonate; this stimulation by nifedipine was reversed by PK 1195, a specific antagonist for the peripheral benzodiazepine binding site. Verapamil (5 microM), on the other hand, antagonized the stimulation of the oxidative burst by benzodiazepines. The data suggest some possible interaction of Ca2+-channel blockers at the benzodiazepine binding site or at a secondary step in the activation mechanism. None of the molecules modulated the calcium influx triggered by arachidonate. Instead, the oxidative response of P 388D1 cells to arachidonate was inhibited by K+-channel blockers, quinidine and tetraethylammonium bromide.

Animals↗
PubMed1987

Fluoride effects on 31P NMR spectra of macrophages.

31P High resolution nuclear magnetic resonance studies have been carried out on the P388D1 tumoral cell line and the BCG elicited alveolar rabbit macrophages both in sedimented cells and in perfused agarose-embedded cells. When the cells were sufficiently oxygenated, the phosphorylated sugars and ATP concentrations attained high levels. The intensity of the peak representing phosphorylated sugars varied inversely with ATP level when macrophagic cells were treated by NaF. The identities of the phosphorylated sugars were revealed by 1H and 31P NMR studies of the P 388D1 cells perchloric extracts.

Adenosine Triphosphate↗
PubMed1987

Peripheral benzodiazepines enhance the respiratory burst of macrophage-like P388D1 cells stimulated by arachidonic acid.

P388D1, a murine cell with macrophage properties, responds to exogenous arachidonic acid with superoxide anion production. This oxidative burst is enhanced by peripheral and mixed type benzodiazepines and this stimulation is specifically reversed by the peripheral antagonist PK 11195. In contrast, PK 11195 is unable to antagonize a stimulation caused by a non-benzodiazepine ligand such as the chemotactic peptide fMet-Leu-Phe. The optimal concentrations were close to 10 nM and corresponded to the affinities of the compounds for the peripheral benzodiazepine receptor detected on these cells. Compared to other tissues where peripheral benzodiazepines acted only at micromolar concentrations, the macrophage with its functional receptor appears as a privileged site of action for these molecules.

Animals↗
PubMed1986

Structure activity relationship in heparin: stimulation of non-vascular cells by a synthetic heparin pentasaccharide in cooperation with human acidic fibroblast growth factors.

Heparin enhances strongly the mitogenic properties of human acidic fibroblast growth factor (h-aFGF) on hamster fibroblast (CCL 39) or bovine lens epithelial cells (BEL). We report here that a synthetic heparin pentasaccharide with high affinity for antithrombin III has the same effect as heparin at about the same concentration. Thus a pentasaccharidic sequence may represent the shortest heparin structure which interacts with h-aFGF.

Animals↗
PubMed1986

Effect of heparin on the stimulation of non-vascular cells by human acidic and basic FGF.

We have purified acidic and basic fibroblast growth factors from human brain (h-aFGF, h-bFGF) and studied the effect of heparin on the growth stimulation by these factors of hamster fibroblast CC139 cells and bovine epithelial lens (BEL) cells. In both the presence and the absence of foetal calf serum (FCS) heparin cooperates with h-aFGF in a dose dependent manner to stimulate both types of cells. The cooperation with h-bFGF is much less. An unpurified human brain fraction containing both factors behaves differently: in the absence of FCS, heparin enhances the activity of the crude fraction on BEL cells, while in the presence of FCS, it decreases this activity. These results indicate that heparin cooperates strongly with h-aFGF to stimulate non-vascular cell proliferation while in a partially purified extract and in the presence of serum it can induce the opposite effect.

Animals↗
PubMed1986

Modulation of protein expression in murine bone marrow cells following in-vivo cytosine arabinoside treatment.

The technique of SDS-PAGE followed by autoradiography was applied to study the changes in protein synthesis occurring in murine bone marrow cells in response to AraC administration. It was found that following AraC injection the medullary population undergoes pronounced changes in protein synthesis. Marked increases were noted in the 20, 28 and 70 kD protein labelling, concomitantly with CFU-S stimulating activity of the AraC treated mice bone marrow conditioned medium.

Animals↗
PubMed1986

In vivo immunomodulating activity of PK 1195, a structurally unrelated ligand for "peripheral" benzodiazepine binding sites--I. Potentiation in mice of the humoral response to sheep red blood cells.

PK 11195, an isoquinoline carboxamide compound with the highest affinity for the peripheral type benzodiazepine binding site has been shown to enhance the humoral response of mice to sheep red blood cells, a T cell dependent antigen. The compound was active when administered i.p. 1 day following immunization. The active doses ranged from 10 ng to 1 mg/kg. Such an immunomodulating activity might be related to the presence of peripheral type benzodiazepine binding sites, previously detected on the macrophage.

Adjuvants, Immunologic↗
PubMed1985

Cyclic AMP response to various haemopoietic regulators.

Diffusible inhibitors and stimulators are involved in the regulation of bone marrow pluripotent stem cell (CFU-S) proliferation. We have previously shown the existence of CFU-S inhibitors in foetal calf marrow and liver and have started their purification. The lack of a simple and time-saving test to determine the kinetic state of CFU-S and the activity of the inhibitors led us to explore the possibility of a biochemical proliferation marker that could be used for screening purpose. Since it was shown that cyclic AMP was implicated in the regulation of CFU-S proliferation, it was of interest to study the variations in cAMP levels after stimulation and inhibition of CFU-S entry into cycle. The results of in vitro experiments showed that the increase in cAMP levels observed in bone marrow cells after incubation with different haemopoietic stimulators was specific neither for bone marrow cells nor for the various haematopoietic regulators. In the in vivo experiments, an increased cAMP level was observed 8 hr after one injection of Ara-C at the time when CFU-S are recruited into S phase. However, no modification of cAMP levels has been observed after injection of CFU-S inhibitors in the Ara-C-treated mice. Although cAMP does not seem to be a suitable marker for testing the activity of inhibitory fractions during the purification process, this work has contributed to the study of CFU-S stimulators.

Animals↗