PAF and haematopoiesis: III. Presence and metabolism of platelet-activating factor in human bone marrow

AbstractPlatelet-activating factor (PAF) is a phospholipid compound with major immunoregulatory activities. The present study shows that human bone marrow contains 576 ± 39 pg PAF/ml (n = 35). Bone marrow-derived PAF exhibits the same biophysical and biological properties that synthetic PAF. PAF concentrations in bone marrow are correlated with the granulocyte (r = 0.4, P = 0.02) but not with the lymphocyte (r = 0.24, P = 0.17) and the monocyte (r = 0.12, P = 0.48) counts. In bone marrow PAF is inactivated by a plasma PAF acetylhydrolase activity (48.0 ± 2.3 nmol/min per ml, n = 34). Experiments with [3H]PAF indicate that human bone marrow cells actively metabolize this potent molecule by the deacetylation-transacylation pathway. Results of this investigation indicate the permanent presence of significant amounts of PAF in bone marrow suggesting its putative involvement in the processes of bone marrow cell proliferation and maturation

Arachidonic acid and freshly isolated human bone marrow mononuclear cells.

Arachidonic acid (AA), a fatty acid found in the human bone marrow plasma, is the precursor of eicosanoids that modulate bone marrow haematopoiesis. To further our understanding of the role of AA in the bone marrow physiology, we have assessed its incorporation in human bone marrow mononuclear cells. Gas chromatography analysis indicates the presence of AA in their fatty acid composition. In bone marrow mononuclear cells, [3H]-AA is incorporated into triglycerides and is later delivered into phospholipids, a result not observed with blood mononuclear cells. Prelabelling-chase experiments indicate a trafficking of labelled AA from phosphatidylcholine to phosphatidylethanolamine. Stimulation of prelabelled bone marrow mononuclear cells with granulocyte-macrophage colony-stimulating factor (GM-CSF) results in the release of a part of the incorporated labelled AA. Finally, exogenous AA (up to 1 microM) has no significant effect on cell growth. In conclusion, human bone marrow mononuclear cells participate to the control of marrow AA concentrations by incorporating AA into phospholipids and triglycerides. In turn, bone marrow mononuclear cells can release AA in response to the potent haematopoietic growth factor GM-CSF

Tumour necrosis factor-alpha (TNFα) stimulates the growth of human bone marrow stromal cells

This study reports that TNF-α is a potent mitogen for human bone marrow sternal cells in vitro (assessed by [3H]-thymidine incorporation into DNA and cell counts). In contrast, cytokines such as IL-1α, IL-1β, IL-2, IL-3, IL-4, IL-6, LIF, SCF, M-CSF, G-CSF and GM-CSF had no effect. The effect of TNF-α on the growth of human bone marrow stromal cells could be of importance during inflammatory processes which take place in the marrow, for example marrow fibrosis

Platelet-activating factor acetylhydrolase and haemophagocytosis in the sepsis syndrome.

Sepsis syndrome (SS) is associated with depressed PAF acetylhydrolase, the enzyme responsible for the degradation of platelet activating factor. PAF acetylhydrolase is in a large part produced by macrophages, whose inadequate activation with haemophagocytosis is frequent in patients with SS. The aim of this study was to test the hypothesis that PAF acetylhydrolase levels could be affected in these critically ill patients, because of the large amounts produced by activated macrophages in vitro and in vivo in animal models. The levels of serum PAF acetylhydrolase were assessed in 90 SS patients, who were divided into three groups: patients with (n = 34) or without haemophagocytosis (n = 31), and patients without thrombocytopenia (n = 25) who were used as a control group. The number of organ dysfunctions was matched between patients with haemophagocytosis and controls. Normal reference values were obtained in 59 randomly selected blood donors. Circulating levels of PAF acetylhydrolase were significantly (p = 0.0001) decreased in patients with SS (57+/-3 nmol/ml/min, n = 90) when compared with healthy subjects (69+/-3 nmol/ml/min, n = 59). PAF acetylhydrolase levels were greater in the presence of a haemophagocytosis but without statistical significance (64.2+/-6.5 vs. 50.1+/-2.8:p = 0.25). Despite the fact that macrophagic activation stimulates the in vitro release of PAF acetylhydrolase, no difference was found between patients with or without haemophagocytosis. The mechanism and the role of the PAF acetylhydrolase reduction in SS patients remain to be determined

New starch-based radiotracer for lung perfusion scintigraphy

PURPOSE: In order to avoid the microbiological risks linked to human serum albumin macroaggregates (MAA) used for lung perfusion scintigraphy, we developed a new starch-based Tc-99m potential radiopharmaceutical. METHODS: Microparticles were prepared from oxidised starch coupled to natural polyamine for Tc-99m complexation. Suspensions were formulated as ready-to-use kits for easy one-step labelling procedures. RESULTS: Particle-size analysis, electron microscopy, and confocal microscopy were performed for microparticle characterisation, and gave a typical size distribution ranging from 7 to 63 microm, with a homogenous population of spherical or oval-shaped microparticles. Radiochemical purity exceeded 95%, and was stable for at least 8 h. When challenged with histidine and human plasma, labelling was also stable. Dynamic scintigraphic acquisitions and biodistribution studies conducted on healthy Wistar rats showed a tracer accumulation with more than 80% of the ID in the lungs after 15 min. CONCLUSIONS: With clinically significant characteristics such as a lung half-life of 3 h, a lung-to-vascular ratio of 900, and a lung-to-liver ratio of 90, starch-based microparticles exhibit all the qualities for an effective new lung perfusion agent

Volumetric assessment of myocardial viability in rats using 3D double contrast enhanced T1 and T2-weighted MRI

OBJECTIVE: Volumetric evaluation of the myocardial viability post-infarction in rats using 3D in vivo MR imaging at 7 T using injection of an extracellular paramagnetic contrast agent and intravascular superparamagnetic iron oxide nanoparticles in the same imaging session. MATERIALS AND METHODS: Five hours after induction of permanent myocardial infarction in rats (n=6), 3D in vivo T1- and T2-weighted MR Imaging was performed prior to and after Gd-DOTA injection (0.2 mmol/kg) and prior to and after nanoparticle injection (5 mg Fe/kg) to assess infarct size and myocardial viability. RESULTS: 3D MR Imaging using a successive contrast agent injection showed a difference of infarct size after Gd-DOTA injection on T1-weighted images compared to the one measured on T2-weighted images after Gd-DOTA and nanoparticle injection. CONCLUSION: The use of 3D T1- and T2-weighted MR Imaging using a double contrast agents protocol made possible the accurate characterization of myocardial infarction volume and allowed the detection of myocardial viability post-infarction in rats

Interleukin-4 (IL-4), but not IL-10, regulates the synthesis of IL-6, IL-8 and leukemia inhibitory factor by human bone marrow stromal cells

AbstractLeukemia inhibitory factor (LIF), interleukin 6 (IL-6) and IL-8 are important regulators of inflammation and hematopoiesis. Human bone marrow stromal cells regulate marrow hematopoiesis by secreting cytokines. By using reverse-transcriptase polymerase chain reaction (RT-PCR), we demonstrate that human bone marrow stromal cells constitutively express LIF, IL-6 and IL-8 transcripts. By using specific ELISAs, we found that their spontaneous productions of LIF, IL-6 and IL-8 are elevated in response to serum and after stimulation with the pro-inflammatory cytokines IL-1α and TNF-α. The anti-inflammatory cytokine IL-4 reduces their serum- and cytokine-induced LIF secretion. By contrast, IL-4 stimulates their serum- and IL-1α-induced IL-6 synthesis. IL-4 has no effect on the serum-induced IL-8 synthesis by marrow stromal cells, but stimulates their cytokine-induced IL-8 production. The anti-inflammatory cytokine IL-10 has no effect on the serum- and cytokine-induced LIF, IL-6 and IL-8 synthesis by bone marrow stromal cells. RT-PCR experiments reveal the presence of IL-4 receptor α-chain mRNA and IL-10 receptor mRNA in cultured bone marrow stromal cells. The differential regulation by IL-4 of two related cytokines, such as LIF and IL-6, and the enhanced effect of this ‘anti-inflammatory’ cytokine on IL-6 and IL-8 synthesis highlight the tightly controlled regulation and the complexity of the cytokine production within the human bone marrow

Genes encoding multiple forms of phospholipase A(2) are expressed in immature forms of human leukemic blasts.

International audiencenon

In vitro and in vivo evaluation of superparamagnetic iron oxide nanoparticles coated by bisphosphonates: the effects of electrical charge and molecule length.

Physicochemical coating properties are often considered to be determining factors for in vivo characteristics of superparamagnetic iron oxide nanoparticles, used as contrast agent in Magnetic Resonance Imaging (MRI). To investigate the electrical charge (modified by zero, one or two ammonium groups) and the molecule length (3, 5 or 7 methylene chains) effects of bisphosphonate-type coatings, we assessed the complement activation, in vivo plasma and tissue relaxation time alterations of intravenously injected small iron oxide nanoparticles (<25 nm) on male healthy Wistar rats. The presence of ammonium groups induces a weak activation of the complement whatever the size and the concentration of particles, whereas hydroxyethylenebisphosphonate (HEBP)-coated particles are poor complement activators only at the lowest concentration. In vivo, HEBP-coated nanoparticles have the greatest prolonged relaxation time effects, despite their higher negative electrical charge, contrary to two ammonium bearing coatings. No significant differences were observed between mono-ammonium molecular coatings

Assessment of myocardial viability in rats: Evaluation of a new method using superparamagnetic iron oxide nanoparticles and Gd-DOTA at high magnetic field

The aim of this study was to detect salvageable peri-infarction myocardium by MRI in rats after infarction, using with a double contrast agent (CA) protocol at 7 Tesla. Intravascular superparamagnetic iron oxide (SPIO) nanoparticles and an extracellular paramagnetic CA (Gd-DOTA) were used to characterize the peri-infarction zone, which may recover function after reperfusion occurs. Infarcted areas measured from T1-weighted (T1-w) images post Gd-DOTA administration were overestimated compared to histological TTC staining (52% +/- 3% of LV surface area vs. 40% +/- 3%, P=0.03) or to T2-w images post SPIO administration (41% +/- 4%, P=0.04), whereas areas measured from T2-w images post SPIO administration were not significantly different from those measured histologically (P=0.7). Viable and nonviable myocardium portions of ischemically injured myocardium were enhanced after diffusive Gd-DOTA injection. The subsequent injection of vascular SPIO nanoparticles enables the discrimination of viable peri-infarction regions by specifically altering the signal of the still-vascularized myocardium