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Biomedical subjects

A Leon

Publications and source records attributed to A Leon.

At least 109 records · Page 6Linked to original sources
PubMed1992

Characterization of 2,4,5-trihydroxyphenylalanine neurotoxicity in vitro and protective effects of ganglioside GM1: implications for Parkinson's disease.

The neurotoxic properties of 2,4,5-trihydroxyphenylalanine (TOPA; the 6-hydroxylated derivative of dopa) was investigated in cultures of central neurons. Application of solutions of TOPA to cerebellar granule cells resulted in a concentration- and time-dependent neuronal death, with prolonged (24 hr) exposure producing a clear left-handed shift in the dose-response relationship from the one observed with a 60-min exposure (LD50: 4 and 29 microM, respectively). This toxicity was largely blocked by the non-N-methyl-D-aspartate antagonist 6-cyano-7-nitroquinoxaline-2,3-dione. Solutions of TOPA were also toxic to mesencephalic neurons after acute or chronic exposure, displaying the same leftward shift in LD50. This latter preparation contained a minor population of dopaminergic, tyrosine hydroxylase immunopositive cells which were likewise sensitive to the excitotoxic effects of TOPA. Neurotoxic activity of TOPA appeared to depend upon its oxidation in solution, as judged using chemical analysis and reducing agents. The monosialoganglioside GM1 was effective in protecting against neurodegeneration induced by brief or prolonged exposure to solutions of TOPA. These results suggest that an abnormal production or accumulation of TOPA or its oxidation product(s) might be involved in excitotoxicity directed to areas of the brain with dopaminergic innervation, and in other brain areas in Parkinson's disease patients on long-term dopa therapy. The selective action of gangliosides in disrupting the pathological consequences of glutamate receptor activation proposes their use as chemoprophylactic agents for preventing or arresting the neuronal losses accompanying such situations.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1992

In vitro kinetics of 8-methoxypsoralen penetration into human lymphoid cells.

Extracorporeal photochemotherapy (ECPC) requires ex vivo UVA irradiation of blood lymphocytes during the time of the theoretical peak 8-methoxsalen (8-MOP) concentration. The aims of this study were to determine the mechanism of cellular uptake of 8-MOP, its possible saturation and the time needed to reach maximal concentration (Tmax) in lymphoid cells. 8-MOP was measured by liquid chromatography in the supernatant of lymphoid cell suspensions incubated with a known amount of 8-MOP. The kinetics of cellular uptake were determined and showed that equilibrium had already been reached after 2 min and remained constant for at least 60 min. The uptake was independent of temperature (4, 25 and 37 degrees C) and was proportional to the 8-MOP concentration in the supernatant. This indicated that 8-MOP penetrated into lymphoid cells by passive diffusion, rather than by active transport or facilitated diffusion, and was thus a non-saturable process. In addition, intracellular metabolism was negligible. These findings demonstrated that the plasma and lymphocytic Tmax were reached simultaneously and statistical analysis showed them to be significantly correlated, thereby validating the standard ECPC protocol for drug ingestion and lymphocyte irradiation.

Humans↗
PubMed1992

Monosialogangliosides, neuroprotection, and neuronal repair processes.

Gangliosides play important roles in the physiologic operations of the nervous system, in particular that of the brain. Changes in ganglioside composition occur in the mammalian brain not only during development, but also in aging and in several neuropathologic situations. Gangliosides may modulate the ability of the brain to modify its response to signals from the surrounding environment. For example, cultured neurons respond to exogenous gangliosides with changes characteristic of differentiation; these sialoglycosphingolipids also amplify the response of neurons to neurotrophic factors. Additional in vitro studies have shown that monosialogangliosides like GM1 protect against excitatory amino acid-related neurotoxicity by limiting the downstream consequences of receptor overstimulation. Systemic administration of GM1 is efficacious in reducing acute nerve cell damage and in facilitating medium- and long-term functional recovery following various types of injury to the adult mammalian central nervous system. The GM1 protective effects in the acute injury phase likely result, at least in part, from attenuation of excitotoxicity, while long-term functional recovery may reflect GM1 potentiation of neurotrophic factors. The potential therapeutic efficacy of GM1 is encouraged by recent positive clinical findings in acute human stroke, subarachnoid hemorrhage, and spinal cord injury.

Animals↗
PubMed1992

Cellular localization of nerve growth factor-like immunoreactivity in hippocampus and septum of adult rat brain.

The cellular localization of the nerve growth factor-like immunoreactivity (NGF-LIR) has been studied in the intact adult rat brain at the level of the hippocampus and the septum. Immunolabelling for NGF combined with counterstaining with cresyl violet and double immunostaining technique, which allowed simultaneous localization of NGF-LIR and that of astroglial marker -GFAP, were used. The data indicate neuronal localization of NGF-like immunoreactivity and a lack of colocalization of NGF-LIR with the immunoreactivity of GFAP in the hippocampus. These data are consistent with in situ hybridization results for NGF and immunocytochemical results for pro-NGF localization obtained by others. At the septal level, apart from neuronal localization of NGF-LIR, single NGF-like immunoreactive astrocytes have been observed. This suggests that, although to a very small extent, in vivo intact brain astrocytes may, just as astrocytes growing in vitro, synthesize NGF-like molecules. This finding may be of importance in better understanding the trophic support for NGF responsive cholinergic neurones in the brain.

Animals↗
PubMed1991

Nerve growth factor differentially modulates the expression of its receptor within the CNS.

The effect of nerve growth factor on the expression of nerve growth factor receptor in the central nervous system of newborn and adult rats was studied by means of immunohistochemistry with the monoclonal antibody 192-IgG. Both during development and in adulthood, the intracerebroventricular administration of nerve growth factor elicited a pronounced increase of nerve growth factor receptor-like immunoreactivity in the cell bodies and neural processes of the basal forebrain cholinergic nuclei, as compared to cytochrome c-treated rats (controls). A pronounced nerve growth factor-induced increase of nerve growth factor receptor-like immunoreactivity was also observed in central regions innervated by trigeminal and spinal ganglia. A moderate to a marked increase of nerve growth factor receptor-like immunoreactivity was evident in some mesencephalic visual system-related structures and thalamic nuclei expressing nerve growth factor receptor. In contrast, NGF treatment did not induce appreciable modification of nerve growth factor receptor-like immunoreactivity in cerebellar, brainstem, and spinal motor structures of newborn rats. In adult nerve growth factor-treated rats, a decrease of nerve growth factor receptor-like immunoreactivity was detected in the cerebellum, whereas no re-expression of nerve growth factor receptor-like immunoreactivity occurred in the motor structures that had expressed it in the first postnatal week. Finally, nerve growth factor was also found to enhance, in both adult and newborn rats, nerve growth factor receptor-like immunoreactivity associated with ependymal and subependymal cellular elements of the lateral and third ventricles, as well as with the leptomeninges overlying the superior colliculus and supraoptic area. The present results indicate that endogenous nerve growth factor or nerve growth factor-like molecules may play a dynamic role in a variety of cell populations of both the developing and mature mammalian central nervous system. We thus propose the nerve growth factor ability to modulate its receptor in vivo as a novel criterion to define nerve growth factor or nerve growth factor-like molecules, sensitive neuronal, and non-neuronal cells. Whereas this criterion does not intrinsically possess absolute physiological validity, its pharmacological concomitants might be relevant in view of the proposed therapeutical use of this trophic factor.

Aging↗
PubMed1991

Ganglioside GM1 prevents death induced by excessive excitatory neurotransmission in cultured hippocampal pyramidal neurons.

Rat hippocampal pyramidal neurons in culture, exposed 30 min to Mg(2+)-free, glycine-supplemented medium undergo a selective (about 35%) degeneration over the next 24 h. This neuronal injury appeared to result from excitatory synaptic transmission and subsequent activation of N-methyl-D-aspartate (NMDA) receptors, as cell death could be blocked by tetrodotoxin and NMDA, but not non-NMDA, receptor antagonists. Ganglioside GM1, which has recently been described to protect against excitotoxin-induced damage, also prevented the death of hippocampal neurons associated with the above phenomenon. Gangliosides may be a novel therapeutic tool for brain injury associated with epileptic-like activity.

Animals↗
PubMed1991

Zidovudine removal during plasma exchange.

Pharmacokinetics of zidovudine (azidothymidine, AZT) were investigated after oral administration (300 mg every 8 hours) in a human immunodeficiency virus seropositive patient who was also treated with plasma exchange (60 ml/kg). Plasma AZT concentrations were measured using high performance liquid chromatography assay. Plasma exchange clearances reached 1-3.8% of the total clearance. The fraction of AZT removed from separated plasma accounted for only 1% of the administered dose. The contribution of plasma exchange to the elimination of AZT appears to be negligible. Solely on the basis of AZT pharmacokinetic data, no particular dose adjustment appears to be necessary in patients treated with multiple plasma exchanges.

Adult↗
PubMed1991

Excitatory amino acid-induced alterations of cytoplasmic free Ca2+ in individual cerebellar granule neurons: role in neurotoxicity.

The effects of glutamate on intracellular free Ca2+, [Ca2+]i, and neurotoxicity were compared in cerebellar granule neurons in vitro. [Ca2+]i was measured with fura-2 and digital fluorescence imaging microscopy; neurotoxicity was monitored using a vital dye and colorimetric analysis. Glutamate produced dose-dependent increases in [Ca2+]i, which tended to be transient for glutamate concentrations in a range of 0.01-0.5 microM and sustained for higher levels of glutamate. The ED50 for the [Ca2+]i response to glutamate was 6 microM. The LD50 for glutamate-induced neurotoxicity was similar, i.e., 10 microM. The effect of glutamate on [Ca2+]i was greatly diminished when external Ca2+ was removed and blocked by Mg2+ or N-methyl-D-aspartate (NMDA)-type receptor antagonists. The latter conditions as well as preloading granule neurons with the intracellular Ca2+ chelator quin2 largely prevented glutamate cytotoxicity. The neurotoxic effect of glutamate required incubations with the stimulus for 10-20 min at 25 degrees C. Withdrawal of glutamate after this period was accompanied by a prolonged alteration in [Ca2+]i. Pretreatment of the cells with the ganglioside GM1 reduced this late increase in [Ca2+]i as well as the neurotoxic effects of glutamate. This indicates that glutamate-induced neurotoxicity results from a composite of diverse temporal alterations in Ca2+ homeostasis and that blunting any of these components reduces excitotoxicity.

Aminoquinolines↗
PubMed1991

Metabolism of semisynthetic single-chain GM1 derivatives in cerebellar granule cells in culture.

Semisynthetic single-chain GM1 derivatives containing N-acetyl-sphingosine (LIGA4) or N-dichloroacetyl-sphingosine (LIGA20) were recently reported to exert strong protection against glutamate-induced neuronal death in primary cultures of cerebellar granule cells. Elucidation of the molecular mechanism underlying the evoked effect requires knowledge of the metabolic fate of such molecules in the same cultured cells. For this, LIGA4 and LIGA20 were made radioactive on the long chain base moiety and added to cerebellar granule cells in culture in parallel with GM1 ganglioside. The metabolic fate was then investigated. It was found that both these molecules were easily taken up by the cells and promptly metabolized in a fashion qualitatively similar to that of control GM1. The highest amount processed was attributed to the different aggregation properties of LIGAs in solution. Among metabolites, higher accumulation of the single-chain ceramide residues was found after LIGA administration. Interestingly, sphingomyelin was generated, regardless the added compound, suggesting a recycling of the free long chain base.

Animals↗
PubMed1991

Differences in induction of c-fos transcription by cholera toxin-derived cyclic AMP and Ca2+ signals in astrocytes and 3T3 fibroblasts.

The B subunit of cholera toxin, a protein which binds specifically to membrane ganglioside GM1, is known to affect cell growth and differentiation. To investigate the mechanism of these cellular responses at the nuclear level, we used the induction of c-fos in astrocytes and 3T3 fibroblasts as a model. Northern blot analysis showed that treatment with B subunit provokes a rapid and transient expression of c-fos mRNA, independent of a measurable increase in cyclic AMP. The B subunit signal, which is mediated by Ca2+, was compared to cholera toxin and other agents which increase intracellular cyclic AMP levels. In transient transfection assays of astrocytes and fibroblasts, functional analysis of c-fos promoter deletions was used to identify the elements involved in transcriptional activation by B subunit. In astrocytes, the DNA region including the serum response element and the cyclic AMP response element (CRE) are equally required, whereas 3T3 cells require only the CRE for maximal induction. A synergistic effect of signal transduction was mediated by calcium and cyclic AMP on the CRE, being positive in 3T3 cells and negative in astrocytes. Diverse regulatory elements may be thus involved in responses of different cell types to the same extracellular signal. Furthermore, a single regulatory element (CRE) can integrate both calcium and cyclic AMP signals in the control of gene expression.

Animals↗
PubMed1991

Autosomal dominant rod-cone dysplasia in the Rdy cat. 2. Electrophysiological findings.

Electroretinography was performed on cats affected with autosomal dominant rod-cone dysplasia (gene symbol Rdy). In normal kittens it was found that retinal sensitivity increased and rod thresholds decreased as the animals matured. Electroretinogram (ERG) amplitudes were mature by 4.5 weeks and adult timing was attained by 6 weeks of age, consistent with the findings of other workers. In Rdy-affected heterozygous kittens the ERG was absent or barely recordable using conventional corneal contact lens electrodes. However, the enhanced sensitivity of an intravitreal needle electrode permitted the recording of ERGs from affected kittens aged 4.5 weeks and older. The intravitreally recorded scotopic ERG in Rdy-affected kittens was a very low amplitude, largely negative response with prolonged a- and b-wave times-to-peak (two to threefold longer than in comparable recordings from an age-matched normal kitten). The b-wave lacked oscillatory potentials and was relatively small so that the ERG was a-wave dominated. This was attributed to delayed and defective synaptogenesis in the outer plexiform layer of dystrophic retinas. In contrast to normal kittens, the b-wave threshold was higher than that of the a-wave in affected kittens. Photopic responses were unrecordable. The intravitreal ERG was barely recordable in a 5-month-old Rdy-affected cat and was apparently extinguished by 7 months of age. In vitro electroretinography permitted a comparison of the photoreceptor responses (fast PIII) from the isolated retinas of 6-week-old control and Rdy-affected heterozygous kittens. Maximum fast PIII amplitudes were reduced by about 75% in affected retinas compared with age-matched normal retinas (P less than 0.005). The mean fast PIII time-to-peak, at maximum light intensity, in Rdy-affected retinas was prolonged by about 15 msec and was approximately twofold longer than the time-to-peak of normal retinas (P less than 0.005).4+ steeper slope with relatively greater prolongations in time-to-peak at lower luminances compared with normal retinas (P less than 0.025). These changes in temporal characteristics may be explained either by severe disorganization of photoreceptor outer segments or by altered phototransduction kinetics.

Aging↗
PubMed1991

Monosialoganglioside GM1 reduces NMDA neurotoxicity in neonatal rat brain.

Monosialoganglioside GM1 prevents excitatory amino acid (EAA)-related neuronal death in cultured central nervous system (CNS) neurons and reduces the severity of acute brain damage in different experimental models of cerebral ischemia. Using a model of brain damage induced by intracerebroventricular administration of N-methyl-D-aspartate (NMDA) in neonate rats, we evaluated whether GM1 is capable of exerting antiexcitotoxic effects following its systemic administration in vivo. Newborn rats subjected to brain damage by NMDA and contemporaneously treated subcutaneously with GM1 showed significantly reduced (i) loss in hemispheric weight, (ii) loss in tissue choline acetyltransferase activity, and (iii) morphological damage in various brain areas. These results indicate that systemic GM1 treatment is efficacious in reducing EAA-related neuronal damage in vivo and suggest that such a phenomenon may underlie its capability to ameliorate neurological outcome following cerebral ischemia.

Animals↗
PubMed1991

Association between glycoconjugate antibodies and Campylobacter infection in patients with Guillain-Barré syndrome.

In a retrospective study, we have analysed sera from a well-characterised Guillain-Barré syndrome (GBS) patient group for antibodies that react with gangliosides. Of 95 GBS patients and 85 control patients analysed, we found that 14 (15%) of GBS patients but only one control patient had antibodies that react with the gangliosides GM1 and/or GD1b but not GM2, GD1a and GT1b using a sensitive enzyme-linked immunosorbent assay (ELISA). This pattern of reactivity suggests binding to the carbohydrate structure Gal(beta 1-3)GalNAc which is shared between some glycolipids and glycoproteins. Similar antibodies have been found previously in a subpopulation of patients with lower motor neuron disease. In the present study, the predominant immunoglobulin class of these anti-glycoconjugate antibodies was IgG rather than IgM. A correlation was found between the presence of these antibodies and prognosis in terms of disability at 3 and 12 months after presentation. Patients with anti-glycoconjugate antibodies also had a higher incidence of previous Campylobacter infections than the rest of the patient group, although the significance of this remains to be determined.

Antibodies↗
PubMed1991

Choline acetyltransferase messenger RNA expression in developing and adult rat brain: regulation by nerve growth factor.

The polymerase chain reaction (PCR) was used to develop a method for detection and relative quantification of the choline acetyltransferase (ChAT) mRNA in neonatal and adult rat CNS. Oligonucleotide primers derived from a porcine ChAT cDNA sequence were used in coupled reverse transcriptase (RT)-PCR to amplify a cDNA sequence of 206 bp which arises in a cycle- and RNA-dependent manner and which hybridizes with both an internal oligonucleotide and a ChAT cDNA probe. ChAT mRNA was detected in spinal cord, septal area, striatum, cortex and hippocampus but not in cerebellum and cardiac or skeletal muscle. In the septal area, relative quantitative evaluation of ChAT mRNA levels by RT-PCR indicates that this transcript is developmentally regulated and increased following intracerebral administration of nerve growth factor (NGF) to both neonatal and young adult rats. This suggests that the increases of ChAT activity observed in basal forebrain during development or after NGF administration are, at least in part, associated with an increase in corresponding levels of mRNA.

Aging↗
PubMed1991

The tumour associated antigen CA15.3 in primary breast cancer. Evaluation of 667 cases.

CA15.3 preoperatory serum levels have been determined in 667 patients with primary untreated breast cancer and in 193 controls. The relationships between CA15.3 and several clinical and pathological parameters were evaluated. CA15.3 levels showed a highly significant direct relationship with stage, T, pT, N and the number of positive lymph nodes. The close relationship between CA15.3 and the number of positive lymph nodes was also demonstrated in a subgroup of 406 patients in which more than ten lymph nodes had been examined. CA15.3 levels were correlated with tumour size in patients without axillary metastasis as well as with the number of positive lymph nodes in pT1 tumours. CA15.3 was significantly higher in medullary than in ductal carcinoma. No relationships were found between serum CA15.3 and receptor status. We conclude from the present findings that CA15.3 in primary untreated breast cancer is a marker of tumour burden as well as of the tendency of local invasiveness (relationship between CA15.3 and nodal status in pT1 tumours).

Adult↗