RESUMEN
PURPOSE: The purpose of this study is to evaluate, in terms of number of examinations and how effective doses are distributed by location and chronology, the use of CT and nuclear medicine examinations in the management of paediatric oncology patients. MATERIALS AND METHODS: This was a retrospective and descriptive study that included 57 children (13 with neonatal neuroblastoma, 18 with renal tumours, and 26 with lymphoma) over a 5-year period, with the length of monitoring ranging from 1 to 7 years. All CT scans and nuclear medicine examinations were counted, and the effective doses calculated. RESULTS: The majority of the examinations were performed during the first year of management. The cumulative effective doses ranged from 7-152 mSv. The lymphoma group received the highest doses, but fewer than 10% of children received in excess of 100 mSv, as against 40% in the North American study published by Chawla et al. CONCLUSION: The usage of irradiating diagnostic radiological examinations in paediatric oncology produces considerable effective doses, which must lead us to consider evaluating our practices, exploring all possible ways to improve protection from radiation, especially in terms of justifying investigations and using alternatives.
Asunto(s)
Neoplasias/diagnóstico por imagen , Tomografía Computarizada por Rayos X , Adolescente , Niño , Preescolar , Femenino , Hospitales Universitarios , Humanos , Lactante , Masculino , Medicina Nuclear , Dosis de Radiación , Cintigrafía , Estudios RetrospectivosRESUMEN
Lipoblastomas are rare benign mesenchymal tumors of fetal white fat tissue appearing most commonly in children under 3 years of age, and usually affecting the extremities. Only nine cases of intrascrotal lipoblastoma have been reported to our knowledge, and although they are benign, in one case an orchidectomy was performed. We describe two new cases of intrascrotal lipoblastoma, and review the literature.
Asunto(s)
Neoplasias de los Genitales Masculinos/patología , Lipoblastoma/patología , Orquiectomía , Escroto/patología , Neoplasias de los Genitales Masculinos/cirugía , Humanos , Lactante , Lipoblastoma/cirugía , Masculino , Escroto/cirugíaRESUMEN
UNLABELLED: Wormian bones are small bones that are often found within the sutures and fontanelles of the skull. When a child presents an unexplained fracture or fracture(s), osteogenesis imperfecta is usually suggested when an "abnormally high number" of fractures are seen. PURPOSE: To assess the frequency, number, and topography of wormian bones in a "normal" paediatric population. MATERIALS AND METHODS: In a population aged from 0 to 3 years, we retrospectively analysed 605 CT brain scans carried out for a range of indications, excluding cases in which there was a suspicion of constitutional bone disease. RESULTS: In our population, wormian bones were found in 53% of children (n=320): 43% of the children had between one and three (n=260), 10% had four or more (n=60), and 6% had five or more (n=40). There was no significant relationship between the number of wormian bones and the various indications that had led to the CT scan being carried out. Wormian bones in the lambdoid suture were found in by far the greatest numbers. CONCLUSION: Wormian bones are common and can sometimes be numerous without necessarily pointing to osteogenesis imperfecta, since 10% of the children in our study had at least four.
Asunto(s)
Encéfalo/diagnóstico por imagen , Suturas Craneales/diagnóstico por imagen , Interpretación de Imagen Asistida por Computador , Imagenología Tridimensional , Tomografía Computarizada por Rayos X , Encefalopatías/diagnóstico por imagen , Preescolar , Tomografía Computarizada de Haz Cónico , Traumatismos Craneocerebrales/diagnóstico por imagen , Craneosinostosis/diagnóstico por imagen , Femenino , Humanos , Hidrocefalia/diagnóstico por imagen , Lactante , Recién Nacido , Masculino , Plagiocefalia/diagnóstico por imagen , Cráneo/anomalías , Cráneo/diagnóstico por imagenRESUMEN
We have investigated phospholipid redistribution, membrane vesicle shedding, shape change, and granule release following A23187 activation of platelets from a patient with Scott syndrome, characterized by impaired transmembrane migration of phosphatidylserine (PS) accompanied by haemorrhagic complications, and two of her children. Electron spin resonance spectroscopy measurement of phospholipids redistribution showed that the internalization of PS was unaffected by the disorder but, after activation, PS exposure was significantly reduced in platelets from the homozygous-type patient. Vesicle shedding was also reduced in these platelets. However, the slow redistribution of phosphatidylcholine was similar to that observed in normal platelets. When treated with calpeptin, platelets from the homozygous-type patient, unlike normal or heterozygous Scott syndrome platelets, showed a smoothly rounded shape without filopods after activation. Following A23187 activation of normal platelets, filopod formation was consecutive to the re-exposition of aminophospholipids on the outer leaflet of the plasma membrane, and the existence of a floppase (outward aminoPLs translocase) has been suggested. In homozygous Scott syndrome platelets the deficiency in PS re-exposition, the absence of filopod formation, and low vesicle shedding are correlated with each other, and argue in favour of a disruption of the proposed floppase activity.
Asunto(s)
Trastornos de la Coagulación Sanguínea/sangre , Calcimicina/farmacología , Fosfolípidos/sangre , Activación Plaquetaria/fisiología , Transporte Biológico , Plaquetas/metabolismo , Plaquetas/patología , Membrana Celular/metabolismo , Tamaño de la Célula , Femenino , Humanos , Masculino , Microscopía Electrónica de Rastreo , Fosfatidilserinas/metabolismo , SíndromeRESUMEN
1. Glutamate (Glu) uptake in neurons and astrocytes is essential to prevent the persistence of excitotoxic levels of Glu in the synaptic cleft. 2. We investigated the effect of oxidative stress, which is also involved in ischemia-reperfusion, on the Glu transporter in isolated rat retinal cells. 3. Hydrogen peroxide (H2O2 3-300 microM) decreases the Na+-dependent Glu uptake. This effect is not related to a free radical production and is partly reversed by reducing agents, suggesting a transporter modulation by a redox-related event.
Asunto(s)
Transportadoras de Casetes de Unión a ATP/metabolismo , Ácido Glutámico/metabolismo , Peróxido de Hidrógeno/farmacología , Oxidantes/farmacología , Retina/metabolismo , Sistema de Transporte de Aminoácidos X-AG , Animales , Transporte Biológico , Ratas , Ratas Wistar , Retina/efectos de los fármacosRESUMEN
The fusogenic properties of an amphipathic net-negative peptide (wae 11), consisting of 11 amino acid residues, were studied. We demonstrate that, whereas the free peptide displays no significant fusion activity, membrane fusion is strongly promoted when the peptide is anchored to a liposomal membrane. The fusion activity of the peptide appears to be independent of pH, and membrane merging is an essentially nonleaky process. Thus, the extents of lipid mixing and contents mixing were virtually indistinguishable. Vesicle aggregation is a prerequisite for fusion. For this process to take place, the target membranes required a positive charge which was provided by incorporating lysine-coupled phosphatidylethanolamine (PElys). The coupled peptide, present in one population, could thus cause vesicle aggregation via nonspecific electrostatic interaction with PElys. However, the free peptide failed to induce aggregation of PElys vesicles, suggesting that the spatial orientation of the coupled peptide codetermined its ability to bring about vesicle aggregation and fusion. With the monitoring of changes in the intrinsic Trp fluorescence, in conjunction with KI-quenching studies, it would appear that hydrophobic interactions facilitate the fusion event, possibly involving (partial) peptide penetration. Such a penetration may be needed to trigger formation of a transient, nonbilayer structure. Since lysophosphatidylcholine inhibited while monoolein strongly stimulated peptide-induced fusion, our data indicate that wae 11-induced fusion proceeds according to a model consistent with the stalk-pore hypothesis for membrane fusion.
Asunto(s)
Liposomas/metabolismo , Fusión de Membrana , Oligopéptidos/metabolismo , Biotina , Fluorescencia , Colorantes Fluorescentes , Glicéridos/farmacología , Concentración de Iones de Hidrógeno , Cinética , Lisina , Lisofosfatidilcolinas/farmacología , Oligopéptidos/química , Fosfatidiletanolaminas/metabolismoRESUMEN
The cytochrome P450scc tryptophan fluorescence was studied by the use of the three quenchers acrylamide, 25-doxyl-27-nor-cholesterol (CNO) and potassium iodide (KI). All the nine tryptophan residues were accessible to acrylamide. Whereas a strong interaction (static quenching) between acrylamide and tryptophan in the active site had been found previously for cytochrome P450c21 [Narasimhulu, S. (1988) Biochemistry 27, 1147-1153], in the case of P450scc the temperature dependence of the slope of the linear Stern-Volmer plots indicated a dynamic quenching mechanism. This mechanism was confirmed by fluorescence lifetime measurements. Of the three observed life-times tau 1 = 3.1 +/- 0.5 ns, tau 2 = 0.7 +/- 0.25 ns and tau 3 = 20 +/- 10 ps, tau 1 decreased noticeably as a function of the acrylamide concentration. CNO, a spin-labeled substrate which is known to bind tightly to the substrate-binding site of P450scc, quenched 15.5% of the total fluorescence. The Lehrer plot of this compound indicated a static quenching process with a reciprocal quenching constant of 1/Ks = 4 microM, a value which is in accord with the dissociation constant. Our data indicate that CNO quenches selectively one or two tryptophan residue(s) in the active site. The fluorescence spectrum of the residue(s) accessible to CNO was characterized by a red-shifted emission maximum (from 332 nm to 336 nm). The same residue(s) appeared to be quenched by potassium iodide, although much less effectively (1/Ks = 0.12 M). The most probable candidate for a complex formation with CNO is Trp417, which is rather close to Cys422 (the fifth heme ligand). Four arginine residues (Arg411, Arg420, Arg425 and Arg426) in the heme peptide may constitute the iodide-binding site.
Asunto(s)
Acrilamidas/química , Enzima de Desdoblamiento de la Cadena Lateral del Colesterol/química , Colesterol/análogos & derivados , Colorantes Fluorescentes , Yoduro de Potasio/química , Triptófano/química , Acrilamida , Secuencia de Aminoácidos , Sitios de Unión , Colesterol/química , Fluorescencia , Datos de Secuencia Molecular , Espectrometría de FluorescenciaRESUMEN
We characterized the physical and biological properties of a 14-residue amphipathic sequence called SFP (for short fusogenic peptide). At acidic pH, this short synthetic peptide interacts with various phospholipidic monolayers. These interactions were correlated with a pH-dependent conformational transition of SFP resulting in a hydrophobic alpha-helical structure. The hemolysis assay showed a pH-dependent weak membrane destabilizing activity of SFP. However, membrane anchoring of SFP through a covalently bound myristic acid enhanced by 1000-fold its membrane-destabilizing power. Moreover, SFP covalently bound to fluorescent-labeled liposomes induced a pH-dependent mixing of both membranes. SFP, a small synthetic peptide, is thus able to mimick many aspects of viral protein-induced membrane fusion: conformational change, membrane destabilization, membrane anchoring and finally pH-dependent lipid mixing.
Asunto(s)
Membrana Celular/efectos de los fármacos , Péptidos/farmacología , Secuencia de Aminoácidos , Hemólisis/efectos de los fármacos , Humanos , Concentración de Iones de Hidrógeno , Liposomas , Datos de Secuencia Molecular , Péptidos/administración & dosificación , Estructura Secundaria de ProteínaRESUMEN
The effect of benzyl alcohol on the transverse mobility and repartition of phospholipids in the human erythrocyte membrane was investigated using electron spin resonance and morphological modification of red blood cells. Transmembrane internalization rates and equilibrium distribution in red blood cells of short-chain spin-labeled phosphatidylcholine, phosphatidylethanolamine and phosphatidylserine were strongly modified by treatment with 10-70 mM benzyl alcohol. A dual effect was observed: (a) at 4 degrees C and 37 degrees C there was an N-ethylmaleimide-sensitive, long lasting and fully reversible increase in the spin-labeled phosphatidylserine and phosphatidylethanolamine internalization rate; (b) at 37 degrees C, an enhancement of N-ethylmaleimide-insensitive fluxes of all the labeled phospholipids through the membrane occurred. Both effects were dose-dependent. Erythrocytes submitted to benzyl alcohol incubation also showed dose-dependent shape changes: an immediate one from discocytes to echinocytes, followed by a slower N-ethylmaleimide- and ATP-dependent change to stomatocytes. Moreover, benzyl alcohol treatment was shown to lead to enhanced hydrolysis of intracellular ATP. All the effects of benzyl alcohol can be described as an accumulation of labeled phosphatidylethanolamine (and labeled phosphatidylcholine at 37 degrees C) in the inner leaflet. This can be interpreted as a perturbation of the erythrocyte membrane, leading to an energy-consuming specific increase in aminophospholipid translocase activity, in addition to a slow and passive bidirectional flux of all phospholipids at 37 degrees C.
Asunto(s)
Alcoholes Bencílicos/farmacología , Membrana Eritrocítica/efectos de los fármacos , Proteínas de Transferencia de Fosfolípidos , Fosfolípidos/metabolismo , Adenosina Trifosfato/metabolismo , Alcohol Bencilo , Transporte Biológico/efectos de los fármacos , Calcimicina/farmacología , Proteínas Portadoras/metabolismo , Diamida/farmacología , Espectroscopía de Resonancia por Spin del Electrón , Deformación Eritrocítica/efectos de los fármacos , Membrana Eritrocítica/enzimología , Membrana Eritrocítica/metabolismo , Etilmaleimida/farmacología , Humanos , Hidrólisis , Cinética , Proteínas de la Membrana/metabolismoRESUMEN
The electron paramagnetic (EPR) properties of a transient species detected during a cytochrome P450 (P450)-mediated peroxidative reaction have been compared with those of peroxidases Compound I and model metalloporphyrins. The reaction which was studied with cholesterol-specific P450scc and (20R)-20-hydroperoxycholesterol, occurred without enzyme denaturation. The resulting transient species, which reached its maximum after 50 s reaction, was characterized by a one-line EPR spectrum, g = 2.0035, delta 1/2 = 1.08 mT. The decay of this radical was concomitant with the production of (20R)-20,21-dihydroxycholesterol. The reaction (almost 100% yield) conserved the stereo-specificity of the natural pathway. We suggest this intermediate is a candidate for the in vivo ultimate oxidant in the P450-mediated hydroxylation process. The comparison of the observed EPR spectrum with those of peroxidase Compound I and related synthetic models allows us to propose a FeIV porphyrin II cation radical structure for the intermediate.
Asunto(s)
Corteza Suprarrenal/enzimología , Enzima de Desdoblamiento de la Cadena Lateral del Colesterol/metabolismo , Animales , Monóxido de Carbono/metabolismo , Bovinos , Colesterol/análogos & derivados , Colesterol/metabolismo , Espectroscopía de Resonancia por Spin del Electrón , Radicales Libres , Hidroxicolesteroles/metabolismo , Hidroxilación , Cinética , Oxidación-Reducción , Unión ProteicaRESUMEN
A paramagnetic analogue of cholesterol (called 25-doxyl-27-norcholesterol (CNO)), labeled near the w-end of the hydrophobic tail, was used to study interactions of cholesterol with filipin. We observed by electron microscopy that CNO- and cholesterol-filipin complexes are structurally equivalent. Two kinds of complexes were seen by ESR spectroscopy and electron microscopy, depending on the stoichiometric R ratio between the antibiotic and sterol. When R was high, an immobilized ESR spectrum appeared, showing strong imbrication between CNO and filipin. When R was nearer to unity, an exchange-broadened spectrum emerged, corresponding to a new phase that was very rich in CNO (a fast exchange between spins could occur by nearest contacts). CNO was easily displaced from its complex (i) by gradual addition of genuine cholesterol; and (ii) by an excess of phospholipids, owing to the very poor affinity of CNO (and cholesterol, by extension) for filipin in the lipidic phase. Almost no difference appeared between the ESR spectra of oriented samples, i.e. the probe showed no long-range order in any complex of CNO with filipin.
Asunto(s)
Colesterol/análogos & derivados , Filipina/metabolismo , Membrana Dobles de Lípidos , Lípidos de la Membrana/metabolismo , Polienos/metabolismo , Colesterol/metabolismo , Espectroscopía de Resonancia por Spin del Electrón , Microscopía ElectrónicaRESUMEN
The cholesterol analogue 25-doxyl-27-nor-cholesterol (CNO), was found to be a substrate for cytochrome P-450scc. Upon incubation with the cytochrome P-450scc electron transfer system, CNO is transformed to pregnenolone (Km = 33 microM, Vmax = 0.32 min-1). The pregnenolone formation from endogenous cholesterol is strongly inhibited by CNO (50% at 5 microM). It binds tightly to cytochrome P-450scc as evidenced by a reversed type I spectral absorbance change (Kd = 5.9 microM) which is paralleled by a greater hyperfine splitting of the room-temperature CNO ESR spectrum due to an enhanced probe immobilization (Kd = 1.9 microM). This finding is in accord with a rotational correlation time of about 10(-7) s, which is close to the tumbling rate of the protein. At 110 K the CNO-bound cytochrome P-450scc displays the ESR g-values gx = 2.404/2.456, gy = 2.245 and gz = 1.916; these are different from those of cholesterol-liganded cytochrome P-450scc and may thus serve as a marker for cytochrome P-450scc. Our data indicate that the stereospecificity of the cytochrome P-450scc side-chain-cleaving activity is not dependent on the nature of the cholesterol side-chain termination (C25 to C27). The substrate binding site is however rather sensitive to a modification of the side chain. The doxyl ring confers a stronger affinity of the substrate to the enzyme. Upon binding it becomes embedded in the protein matrix, and we estimate that its final position is 0.6-1.0 nm from the heme moiety.
Asunto(s)
Enzima de Desdoblamiento de la Cadena Lateral del Colesterol/análisis , Colesterol/análogos & derivados , Corteza Suprarrenal/análisis , Corteza Suprarrenal/enzimología , Animales , Sitios de Unión/efectos de los fármacos , Bovinos , Colesterol/farmacología , Transporte de Electrón , Cromatografía de Gases y Espectrometría de Masas , Mitocondrias/análisis , Mitocondrias/enzimología , Pregnenolona/aislamiento & purificación , Marcadores de SpinRESUMEN
The synthesis of a new paramagnetic (nitroxide) analogue of cholesterol is described. This compound (called CNO) contains a doxyl group in the lateral chain at position 25. Our results show that CNO retains three molecular interactions which characterize authentic cholesterol: It assumes an orientation perpendicular to the phospholipid bilayer with the doxyl group buried in the membrane core, as seen by ESR spectroscopy. It widens the transition temperature of dimyristoylphosphatidylcholine, to the same extent as cholesterol, as measured by Raman and ESR spectroscopies. It interacts with polyene antibiotics, such as amphotericin B and filipin, in the same manner as its model. This was proved on the one hand by the change in fluorescence of self quenched vesicle-entrapped calcein, after dilution in the external medium, provoked by filipin, and on the other hand by fluorescence quenching provoked by cobalt ions entering the vesicles under the influence of amphotericin B. We concluded that CNO, although it has a side chain different from genuine cholesterol, can help to solve many physiologically meaningful questions related to the distribution and movement rate of cholesterol itself.
Asunto(s)
Colesterol/análogos & derivados , Fosfatidilcolinas , Anfotericina B , Espectroscopía de Resonancia por Spin del Electrón , Filipina , Modelos Biológicos , Conformación Molecular , Espectrometría de FluorescenciaRESUMEN
We have used ESR and NMR linewidth broadening by spin-labels to determine the overall orientation of spin-labeled analogues of cholesterol and androstanol in egg lecithin bilayers. While the cholesterol analogues were found to have a single orientation in each monolayer, with the acyl chain pointing towards the center of the bilayer, the androstanol analogue appeared, at least in sonicated vesicles, to experience two opposite orientations in the same monolayer, very likely with a rapid reorientation. The possibility of rapid vertical fluctuations of the sterol molecules within the phospholipid bilayer is also discussed.
Asunto(s)
Androstanoles , Colesterol , Membrana Dobles de Lípidos , Espectroscopía de Resonancia por Spin del Electrón , Espectroscopía de Resonancia Magnética , Matemática , Marcadores de Spin/metabolismoRESUMEN
The multistep synthesis of a photoreactive, radioactive and aggregating analogue of platelet-activating factor (PAF)-acether is described. The photoreactive and radioactive moiety was added at the last step; the specific radioactivity was higher than 1000 Ci/mmol. The concentration of this new analogue which causes 50% of aggregation of platelets were of the same order of magnitude as for synthetic snPAF-acether, so as for two other analogues having a bulky group at the omega end of the fatty ether chain. The photoreactivity was proved by the covalent binding of the analogue to protein (BSA) after 10-min irradiation times at 300 nm. The binding was largely prevented by prior (not by later) addition of a high concentration of lyso phosphatidyl choline.