Biomedical subjects

J Hugon

Publications and source records attributed to J Hugon.

At least 37 records · Page 2Linked to original sources

PubMed1997

Glutamate toxicity enhances tau gene expression in neuronal cultures.

Tau protein is a microtubule-associated protein normally expressed in neurons. In Alzheimer's disease (AD) brains, phosphorylated tau accumulates in paired helical filaments which form neurofibrillary tangles in affected neurons; moreover, tau mRNA expression is increased in affected regions of AD brains. Glutamate, an excitatory neurotransmitter but also a potent neurotoxin under pathologic conditions, is known to produce neuronal degeneration and death accompanied by an increase in tau immunoreactivity in primary neuronal cultures. The goal of the present study is to evaluate the effects of glutamate on tau gene expression in neuronal cultures. We report a delayed and long-lasting enhancement of tau mRNA expression after a 15 min exposure to toxic concentrations of glutamate: neuronal tau mRNA levels reach a peak after 3 hr and remain increased 6 and 12 hr after the end of glutamate exposure. Both NMDA and AMPA/ kainate receptors are involved in this tau gene overexpression. Actinomycin D prevents this tau mRNA induction indicating that transduction signals elicited by glutamate act at the transcriptional level. The role of this delayed tau overexpression is not elucided but could be linked to either a reactive survival process or to a programmed cellular degeneration.

Animals↗

PubMed1997

NMDA induces apoptosis and necrosis in neuronal cultures. Increased APP immunoreactivity is linked to apoptotic cells.

In rat neuronal cultures exposed for a prolonged period (16 h) to a low concentration of N-methyl-D-aspartate (NMDA; 20 microM) two different types of neuronal death were observed, necrosis and apoptosis. The immunocytochemical study of necrotic neurons revealed the absence of amyloid precursor protein (APP) labeling in the cytoplasmic region. In contrast, neuronal apoptosis was associated with an increase in cytoplasmic APP immunoreactivity. In addition, the presence of extracellular APP was also detected around some apoptotic neurons, suggesting that apoptosis could contribute to the presence of extracellular APP.

Amyloid beta-Protein Precursor↗

PubMed1997

Neuronal APP accumulates in toxic membrane blebbings.

The occurence of plasma membrane blebbings is an early cytotoxic event, associated with the reorganization of cytoskeletal proteins, the alteration of interactions between the plasma membrane and the underlying cytoskeleton. The blebbing formation remains poorly understood but the involvement of cytosolic Ca2+ and the production of free radicals may contribute to this cellular phenomenom. The amyloid precursor protein (APP), is a transmembrane protein that can be cleaved to produce the beta amyloid peptide (Abeta) which accumulates in brain senile plaques of Alzheimer's disease. Our study reveals that the exposure of rat and human (hNT) neuronal cultures to a mild concentration of the excitotoxin NMDA slowly induces perturbations of the neuronal cytoskeleton and the occurence of plasma membrane blebbings. An immunocytochemical study using four different APP antibodies demonstrates that these membrane blebs are also associated with a redistribution and an accumulation of cellular APP. This phenomenon is linked to a Ca2+-influx through NMDA-receptors since it is prevented by the NMDA antagonist MK801 or by Ca2+-depleted conditions. In conclusion this study shows that neuronal degeneration induced by slow excitotoxicity, is associated with the presence of APP-accumulating blebs, that can be secondly released in the extracellular region.

Amyloid beta-Protein Precursor↗

PubMed1997

Therapeutic advances in amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is a progressive and rapidly fatal neurodegenerative disease in which both upper and lower motoneurones are involved. The recent discovery of mutations affecting the superoxide dismutase (SOD) gene has given impetus to research on the role of oxidative stress in the pathogenesis of familial ALS, while further evidence for a role of excitotoxicity in the disease process has arisen. In this review, Erik Louvel, Jacques Hugon and Adam Doble discuss these findings and, in addition, describe how a number of large, well-controlled clinical trials have taken place to test potential therapies suggested by different aetiological hypotheses, including immunosuppressive therapies, neurotrophic factors, antioxidants and anti-excitotoxic drugs. These trials have led to the first modest steps in the treatment of this devastating neurological disease.

Amyotrophic Lateral Sclerosis↗

PubMed1997

Cultured neurons expressing phosphorylated tau are more resistant to apoptosis induced by NMDA or serum deprivation.

Apoptosis is a programmed cell death that occurs during the development of the nervous system and in neurodegenerative disorders. Tau protein is a cytoskeletal component that promotes microtubule polymerization and stabilization. Apoptosis was induced in primary neuronal cultures by a prolonged exposure (16 h) to the NMDA (N-methyl-D-aspartate 20 microM) or by serum deprivation. The percentages of apoptotic neurons expressing phosphorylated tau (AT8) immunoreactivity are comparable in control and NMDA-exposed cultures (7.5 +/- 1.9 and 6.9 +/- 1.9%, respectively). At the opposite, the percentage of apoptotic neurons expressing de-phosphorylated tau (tau 1) immunolabelings is dramatically increased in NMDA-treated cultures (X 2.3 of controls). Similar results were also observed 48 h after serum deprivation. These results demonstrate in vitro that under these conditions, resistant and sensitive cortical neurons to apoptosis can be partly differentiated according to their phosphorylated tau immunoreactivities.

Animals↗

PubMed1997

Increased hypoxic tolerance by chemical inhibition of oxidative phosphorylation: "chemical preconditioning".

A short ischemic episode preceding sustained ischemia is known to increase tolerance against ischemic cell death. We report early-onset long-lasting neuroprotection against in vitro hypoxia by preceding selective chemical inhibition of oxidative phosphorylation: "chemical preconditioning." The amplitude of CA1 population spikes (psap) in hippocampal slices prepared from control animals (control slices) was 31 +/- 27% (mean +/- SD) upon 45-min recovery from 15-min in vitro hypoxia. In slices prepared from animals treated in vivo with 20 mg/kg 3-nitropropionate (3-np) 1-24 h prior to slice preparation (preconditioned slices), psap improved to 90 +/- 15% (p < 0.01). Posthypoxic oxygen free radicals were reduced to 65 +/- 10% (mean +/- SD) of control in preconditioned slices (p < 0.05). Posthypoxic neuronal density improved from 52 +/- 15% (mean +/- SD) in control slices to 97 +/- 23% in preconditioned slices (p < 0.001). Glibenclamide, an antagonist at KATP-channels, partly reversed increased hypoxic tolerance. We conclude that chemical preconditioning induces early-onset long-lasting tolerance against in vitro hypoxia. Ultimately, this strategy may be applicable as a neuroprotective strategy in humans.

Adenosine Triphosphate↗

PubMed1997

Identical chromosome imbalance in two siblings born to a mother with a double reciprocal translocation.

We report the case of a woman who carried two reciprocal translocations. Her karyotype was 46,XX,t(3;12)(q12;q21)(4;17)(p14;p13). She had two children, a phenotypically normal daughter (karyotype (46,XX,t(3;12)(q12;q21)) and a son with partial 4p trisomy (karyotype 46,XY,t(3;12) (q12;q21),-17,+maternal der(17)). She was pregnant with a female fetus who had the same karyotype as her son. She also reported a history of two spontaneous abortions. This viable recurrent abnormality was due to the maternal (4;17) translocation with meiotic segregation type 2:2 adjacent 1. In this case of the two reciprocal translocations carried by the mother, one led to imbalances, whereas the other remained balanced in the viable offspring.

Adult↗

PubMed1996

Antioxidant drugs block in vitro the neurotoxicity of CSF from patients with amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is a progressive neurological disease characterized by upper and lower motoneurone degeneration. Excitotoxicity and oxidative stress have been proposed as possible aetiological factors. We measured the neuronal death induced in rat cortical cell cultures by CSF taken from seven ALS patient and seven control subjects with lumbar radiculopathies. Cultures were exposed to CSF for 48 h at a dilution of 1:4. Some cultures were also exposed to antioxidant drugs, the free radical scavenger vitamin E (250 microM) and the xanthine oxidase inhibitor allopurinol (50 microM), alone or combined. The mean neuronal death rate was 31.8 +/- 3.4% in cultures exposed to ALS CSF and 10.9 +/- 1.8% in cultures exposed to control CSF. The cytotoxicity of ALS CSF was partially blocked by vitamin E (21.6 +/- 3%) or by allopurinol (18.6 +/- 2.7%). The combination of these two antioxidants reduced the toxicity from 31.8 +/- 3.4% to 10.6 +/- 1.7%. The present work suggests that neurotoxicity induced by CSF from patients with ALS indirectly involves free radicals. A combination of allopurinol and vitamin E may be useful in ALS therapy.

Adult↗

PubMed1996

The presence of calbindin in rat cortical neurons protects in vitro from oxydative stress.

Free radicals are highly reactive chemicals containing an unpaired electron and are normally produced by the cellular metabolism. The oxydative stress is defined as a lack of balance between the production of free radicals and the activity of antioxydant metabolites. It induces cellular damages to lipids, proteins and membranes. Abnormal calcium metabolism can be a consequence of oxydative stress leading to increased intracellular concentrations. Calbindin D28K is a calcium binding protein which could have a neuroprotective action against various cellular insults. In this study rat cortical cell cultures were exposed during various times and at different concentrations to the couple Xanthine/Xanthine oxydase (XA/XO), which produces the superoxyde radical O2-.. Neuronal survival revealed that XA/XO is toxic for cortical cell cultures. The Calbindin D28K immunocytochemical study shows that the percentages of Calbindin positive cells are greater in surviving neurons following the XA/XO exposure compared to controls. There is a time-dependent and a dose-dependent relation between the number of surviving neurons and the percentage of Calbindin positive neurons. These results suggest that the presence of cytosolic neuronal Calbindin D28k is associated with a greater resistance to oxydative stress.

Animals↗

PubMed1996

Phorbol ester enhances phosphorylated tau protein immunoreactivity in neuronal cultures.

One of the hallmarks of Alzheimer's disease (AD) is neurofibrillary degeneration which results from the aggregation of phosphorylated tau proteins into paired helical filament (PHF) structures. AD2 is a new monoclonal antibody raised against PHF tau which detects neurofibrillary tangles in AD brain. In primary neuronal cultures, phorbol ester treatment induced a time- and dose-dependent increase in AD2 immunoreactivity quantified by laser confocal microscopy and immunoblottings. Alkaline phosphatase treatment reversed these immunocytochemical changes. These results suggest that the modifications of neuronal metabolism induced by phorbol ester including protein kinase C activation produce an increase in phosphorylated tau immunoreactivity.

Animals↗

PubMed1996

Modifications of neuronal phosphorylated tau immunoreactivity induced by NMDA toxicity.

Glutamate toxicity has been involved in the pathophysiology of a large variety of neurodegenerative disorders. Tau Protein is a micro-tubule-associated protein that promotes microtubule polymerization and stabilization. Phosphorylated tau protein accumulates in paired helical neurofilaments, the major constituent of neurofibrillary tangles observed in the brain of patients suffering from Alzheimer disease (AD). In this study, using confocal laser microscopy and immunoblot analysis, we report that acute (500 mu M for 15 min) or chronic (20 mu M for 16 h) N-methyl-D-aspartate (NMDA) neuronal toxicities modify the immunoreactivity of phosphorylated tau. Neuronal degeneration produced by N-methyl-D-aspartate is associated with an augmented immunolabeling of phosphorylated tau proteins at serine 202 (AT8 antibody) as observed in paired helical neurofilaments. This finding could help to determine the cellular mechanisms at the origin of neuronal degeneration associated with modifications of phosphorylated tau immunoreactivity produced by receptor-mediated extracellular signals.

Alzheimer Disease↗

PubMed1996

Phosphorylated neurofilament expression and resistance to kainate toxicity.

Antibodies directed against phosphorylated neurofilaments, which are major proteins of the neuronal cytoskeleton, usually do not label neuronal cell bodies except in some neurological diseases. In the present study, we show that in rat cortical cell cultures exposed to kainate there is an inverse relation between neuronal survival and the proportion of neuronal cell bodies stained by a monoclonal antibody (clone SMI31) that recognizes extensively phosphorylated neurofilament proteins (150 kDa and 200 kDa). The immunoblot analysis also revealed an increase in 150-kDa phosphorylated neurofilament expression in kainate-treated cell cultures. Furthermore, the direct quantification of viable neurons SMI31-immunopositive or immunonegative in perikarya showed that the majority of neurons resistant to kainate toxicity expressed phosphorylated neurofilaments in their cell bodies. The percentage of viable neurons displaying SMI31-immunoreactivity in their cell bodies increased from 14.7% in control cultures to 30.0% in cultures treated with 10 microM kainate. These data suggest that phosphorylated neurofilament expression is associated with a reduced cell vulnerability to excitotoxicity induced by kainate.

Animals↗

PubMed1996

NMDA antagonist blockade of AT8 tau immunoreactive changes in neuronal cultures.

Antagonists at four distinct regulatory sites on the N-methyl-D-aspartate (NMDA) receptor were tested for their ability to attenuate NMDA-mediated chronic excitotoxicity and the consequences on AT8 tau immunoreactivity in neuronal cultures. Excitotoxicity was monitored in cultures by diacetate fluorescein staining. Immunoreactivity of tau phosphorylated at serine 202 was quantified by laser confocal microscopy. The NMDA-receptor antagonists MK801, AP7 and 7-chlorokynurenate significantly blocked NMDA-induced cell death and significantly reduced AT8 tau immunoreactivity. NMDA antagonism by the polyamine site antagonist, ifenprodil, did not completely reverse the increase in AT8 tau immunolabeling induced by NMDA and did not completely protect NMDA-sensitive neurons, suggesting an heterogeneity in the NMDA receptor population.

2-Amino-5-phosphonovalerate↗

PubMed1996

ALS therapy: targets for the future.

There are four main hypotheses about the cause of ALS: excitotoxicity linked to glutamate receptor overactivation; mutation of the superoxide dismutase gene; production of autoantibodies to calcium channels; neurofilament accumulation. The motoneuron degeneration characteristic of ALS could be caused by any one or a combination of these mechanisms. Future therapeutic approaches should be based on these mechanisms and given in combination so that different levels of the degenerative process are targeted. Protection against excitotoxicity could be achieved with a combination of pharmacologic agents having neuroprotective activity, such as antiglutamate agents (e.g., riluzole), N-methyl-D-aspartate (NMDA) and non-NMDA antagonists, free-radical scavengers, calcium-channel blockers, and neurotrophic factors. Gene transfer is a possible future approach when causative mutations are identified. Transfer of genes encoding neuroprotective agents or genetically modified cells stably expressing these agents is another possible strategy.

Amyotrophic Lateral Sclerosis↗

PubMed1996

[Role of glutamate and excitotoxicity in neurologic diseases].

Glutamate is one of the major excitatory neurotransmitter in the central nervous system. Glutamate acts on 4 different post synaptic receptors; NMDA (N-Methyl-D-aspartate) AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid), Kainate and metabotropic receptors. The three former receptors are linked to membrane ion channels whereas metabotropic receptors are coupled with a G protein. Glutamate is involved in the physiologic processes of learning, memory and motricity. Glutamate is also a potent neurotoxin responsible for toxic neuronal death of post synaptic neurons. This action has been denominated excitotoxicity and occurs as a consequence of a prolonged or a strong activation of glutamate post-synaptic receptors. The rise in intracellular calcium seems to play a major role in the pathological events following excitotoxicity. The pathophysiology of several acute or chronic neurological disorders has been linked to excitotoxicity. This excitotoxic process could be present in acute neuronal death observed in stroke, hypoglycemia and traumatisms of the central nervous system and in chronic neuronal degeneration observed in Amyotrophic Lateral Sclerosis (ALS), Alzheimer's disease, Parkinson's disease, Huntington's disease and neuro AIDS. A better knowledge of the cellular events induced by excitotoxicity will allow to consider new therapeutic approaches in various neurological disorders.

Acute Disease↗

PubMed1996

Riluzole and ALS therapy.

Amyotrophic lateral sclerosis (ALS) is a severe neurological disorder clinically characterized by progressive muscle weakness, amyotrophy, fasciculations and signs of corticospinal tract deficits. The cause is unknown but several hypotheses are currently proposed. In familial forms of ALS, a mutation of the Cu-Zn superoxide dismutase gene was reported in some patients. Autoimmunity and neurofilament dysfunction were also observed. The last hypothesis is linked to excitotoxicity. This cellular phenomenon is associated with the overstimulation of glutamate post-synaptic receptors, leading to neuronal degeneration. Abnormal glutamate metabolism was also discovered in ALS patients. In these conditions, riluzole, a pharmacological agent that reduces glutamate release from nerve terminals, was administered to ALS patients. Riluzole is an anti-convulsant and a neuroprotective agent and specifically blocks sodium channels in their inactivated states. In a recent double blind placebo controlled study, riluzole was given to 77 patients (placebo 78 patients). After 1 year of treatment 58% of the placebo-treated patients were still alive compared to 74% of patients treated with riluzole. The prolonged survival was significant in the overall population and in the bulbar-onset group.

Amyotrophic Lateral Sclerosis↗

PubMed1995

Calbindin D28K-containing neurons, and not HSP70-expressing neurons, are more resistant to HIV-1 envelope (gp120) toxicity in cortical cell cultures.

HIV-1-associated cognitive/motor complex is one of the major neurological complications of AIDS and is associated with neuronal loss. Gp120, the HIV envelope protein, is toxic for neurons in cultures and produces a rise in intracytosolic calcium. This neurotoxicity is dose-dependent and time-dependent. We evaluated the selective gp120 toxicity in primary neuronal cultures for calbindin-free and calbindin-containing neurons with semi-quantitative immunocytochemistry using an anti-calbindin D28K monoclonal antibody. The number of immunolabelled neurons was inversely correlated to neuronal survival. In cultures exposed to gp120 (100 pM) for 24 hr the neuronal survival of initial platings was 19.7 +/- 2.1% and the percentage of neuronal survival was 84.6 +/- 4.9% in control cultures exposed to the vehicle. The corresponding percentages of immunolabelled neurons were 85.0 +/- 2.1% in treated cultures and 23.6 +/- 3.1% in control cultures (P < 0.001). The expression of heat shock proteins by heating cell cultures did not protect neurons from gp120 toxicity. These results suggest that calbindin D2K28-containing neurons are more resistant to gp120-toxicity in this cell culture system.

Animals↗

PubMed1995

Modulation of tau neuronal expression induced by NMDA, non-NMDA and metabotropic glutamate receptor agonists.

We have analysed changes in tau protein immunoreactivity in rat embryonic neurons degenerating in response to treatment with N-methyl-D-aspartate (NMDA), non-NMDA and metabotropic agonists. Glutamate agonists were applied in Mg(++)-free and glycine-supplemented medium 8 days after initial plating. Cell viability was assessed by fluorescein diacetate staining and neuronal survival was evaluated by cell counting. Immunocytochemical and confocal laser microscopic studies used a tau2 monoclonal antibody. Acute and chronic NMDA treatment induced a concentration-dependent increase in intraneuronal tau immunoreactivity. Increased tau immunolabelling during chronic NMDA toxicity was dramatically attenuated by tetrodotoxin and also by 6-cyano-7-nitroquinoxaline-2,3-dione. Non-NMDA and metabotropic receptor agonist treatment produced a weaker augmentation in tau2 immunoreactivity. These findings suggest that, in this model, glutamate-receptor and sodium-channel coactivation are together needed to produce changes in tau immunoreactivity.

Analysis of Variance↗