Gp120-induced Neurotoxicity Research Articles

Neuronal Apoptotic Signaling Pathways Probed and Intervened by Synthetically and Modularly Modified (SMM) Chemokines

As the main coreceptors for human immunodeficiency virus type 1 (HIV-1) entry, CXCR4 and CCR5 play important roles in HIV-associated dementia (HAD). HIV-1 glycoprotein gp120 contributes to HAD by causing neuronal damage and death, either directly by triggering apoptotic pathways or indirectly by stimulating glial cells to release neurotoxins. Here, to understand the mechanism of CXCR4 or CCR5 signaling in neuronal apoptosis associated with HAD, we have applied synthetically and modularly modified (SMM)-chemokine analogs derived from natural stromal cell-derived factor-1alpha or viral macrophage inflammatory protein-II as chemical probes of the mechanism(s) whereby these SMM-chemokines prevent or promote neuronal apoptosis. We show that inherently neurotoxic natural ligands of CXCR4, such as stromal cell-derived factor-1alpha or viral macrophage inflammatory protein-II, can be modified to protect neurons from apoptosis induced by CXCR4-preferring gp120(IIIB), and that the inhibition of CCR5 by antagonist SMM-chemokines, unlike neuroprotective CCR5 natural ligands, leads to neurotoxicity by activating a p38 mitogen-activated protein kinase (MAPK)-dependent pathway. Furthermore, we discover distinct signaling pathways activated by different chemokine ligands that are either natural agonists or synthetic antagonists, thus demonstrating a chemical biology strategy of using chemically engineered inhibitors of chemokine receptors to study the signaling mechanism of neuronal apoptosis and survival.

Role of the transcription factor E2F1 in CXCR4-mediated neurotoxicity and HIV neuropathology

This study sought to determine the role of the transcription factor E2F1 in CXCR4-mediated neurotoxicity and HIV neuropathology. We studied the effect of the HIV envelope protein gp120 on the expression of E2F1-dependent apoptotic proteins in human and rodent neurons and examined the expression pattern of E2F1 in the brain of HIV-infected individuals. Our findings suggest that in cultured neurons gp120 increased E2F1 levels in the nucleus, stimulated its transcriptional activity and enhanced the expression of the E2F1 target proteins Cdc2 and Puma. Studies with neuronal cultures from E2F1 deficient mice demonstrated that the transcription factor is required for gp120-induced neurotoxicity and up-regulation of Cdc2 and Puma. Levels of E2F1 protein were greater in the nucleus of neurons in brains of HIV-infected patients exhibiting dementia when compared to HIV-negative subjects or HIV-positive neurologically normal patients. Overall, these studies indicate that E2F1 is primarily involved in CXCR4-mediated neurotoxicity and HIV neuropathogenesis.

Neonatal intrahippocampal gp120 injection: An examination early in development

The presence of human immunodeficiency virus type 1 (HIV-1) in the brain is believed to be responsible for mediating the pathogenesis of neurological abnormalities through the viral toxins gp120 and Tat. Numerous studies indicate neurotoxic effects of the HIV-1-protein Tat, with demonstrated neurobehavioral and cognitive alterations. However, less clear is the neurotoxic effect of gp120 on neurobehavior. This study was designed to characterize the potential deficits in sensory-motor and preattentive functions, following intrahippocampal administration of gp120. Using a randomized-block design, male and female pups of eight Sprague–Dawley litters were injected bilaterally with either vehicle (VEH) (1 μl volume) or one of the three gp120 doses (1.29, 12.9, or 129 ng/μl) at postnatal day (P)1. Sensory-motor functions were assessed at P3, as measured by the righting reflex and at P8, as measured by negative geotaxis. At P24 animals were tested on preattentive processes, as indexed by sensorimotor gating. Sensorimotor gating was measured by prepulse inhibition (PPI) of the auditory startle response (ASR) (ISIs of 0, 8, 40, 80, 120, and 4000 ms, six trial blocks, Latin-square design). Results indicated gp120-induced neurotoxicity on the righting reflex but not negative geotaxis. For sensorimotor gating, the PPI test demonstrated a reduced inhibition response on peak ASR latency as the dose of gp120 increased. No effect was noted for response inhibition on peak ASR amplitude. These data suggest that intrahippocampal injection of gp120 (0, 1.29, 12.9, or 129 ng/μl) had transient neurotoxic effects on sensory-motor function and limited effects on preattentive processes early in development.

Evidence for a role of protein tyrosine kinases in cell death induced by gp120 in CHP100 neuroblastoma cells

HIV-1 coat protein gp120 is able to kill neuronal cells in culture. Here we address the possible role of protein tyrosine kinases (PTKs) in gp120-induced neurotoxicity using the CHP100 human neuroblastoma cell line as experimental model. For this purpose, the effect of specific PTK inhibitors like genistein, herbimycin A and lavendustin A was evaluated on CHP100 cell death elicited by the viral protein. Here we report that genistein (1–10 μM) significantly reduced the cytotoxic effects induced by gp120 (10 pM). The same protective action was offered by a pre-treatment with herbimycin A (0.1–1 μM) or lavendustin A (1–10 μM). Conversely, daidzein (1–100 μM), a genistein analogue devoid of PTK inhibitory properties, failed to reduce CHP100 cell death caused by gp120. These findings suggest that PTKs can be involved in the signal transduction cascade by which the glycoprotein induces neurotoxicity.

Human Immunodeficiency Virus Type 1 gp120 and Ethanol Coexposure in Rat Organotypic Brain Slice Cultures: Curtailment of gp120-Induced Neurotoxicity and Neurotoxic Mediators by Moderate but not High Ethanol Concentrations

Human Immunodeficiency Virus Type 1 gp120 and Ethanol Coexposure in Rat Organotypic Brain Slice Cultures: Curtailment of gp120-Induced Neurotoxicity and Neurotoxic Mediators by Moderate but not High Ethanol Concentrations

Update on D-ala-peptide T-amide (DAPTA): a viral entry inhibitor that blocks CCR5 chemokine receptors.

Peptide T, named for its high threonine content (ASTTTNYT), was derived by a database search which assumed that a relevant receptor binding epitope within env (gp120) would have sequence homology to a known signaling peptide. Binding of radiolabeled gp120 to brain membranes was displaced by peptide T and three octapeptide analogs (including "DAPTA", Dala1-peptide T-amide, the protease-resistant analog now in Phase II clinical trials) with the same potency that these four octapeptides blocked infectivity of an early passage patient isolate. This 1986 report was controversial due to a number of laboratories' failure to find peptide T antiviral effects; we now know that peptide T is a potent HIV entry inhibitor selectively targeting CCR5 receptors with minimal effects on the X4 tropic lab adapted virus exclusively in use at that time. Early clinical trials, which demonstrated lack of toxicity and focused on neurological and neurocognitive benefits, are reviewed and data from a small ongoing Phase II trial--the first to assess peptide T's antiviral effects--are presented. Studies using infectivity, receptor binding, chemotaxis, and blockade of gp120-induced neurotoxicity in vitro and in vivo are reviewed, discussed and presented here. Peptide T and analogs of its core pentapeptide, present near the V2 stem of numerous gp120 isolates, are potent ligands for CCR5. Clinical data showing peptide T's immunomodulation of plasma cytokine levels and increases in the percentage of IFNgamma secreting CD8+ T cells in patients with HIV disease are presented and suggests additional therapeutic mechanisms via regulation of specific immunity.

Human immunodeficiency virus type 1 gp120 and ethanol coexposure in rat organotypic brain slice cultures: Curtailment of gp120-induced neurotoxicity and neurotoxic mediators by moderate but not high ethanol concentrations.

Human immunodeficiency virus type 1 (HIV-1) envelope protein gp120, implicated with other retroviral proteins in acquired immunodeficiency syndrome (AIDS)-related dementia, causes neuronal degeneration by inciting cascades of neurotoxic mediators from glia. It also may facilitate neuronal glutamate (N-methyl-D-aspartate, NMDA) receptor-mediated excitotoxicity by interacting at the glycine coagonist site. The authors reported that preconditioning rat organotypic hippocampal-cortical slice cultures subchronically with ethanol at concentrations occurring during moderate drinking (20 to 30 mM) prevented gp120's induction of neurotoxic mediators and intracellular calcium, as well as neuronal death. The authors now find that the acute copresence of ethanol in moderate as opposed to high concentrations similarly blocks the retroviral protein's neurotoxic effects in brain slice cultures, assessed with lactate dehydrogenase (LDH) release and propidium iodide (PI) labeling. As with ethanol preconditioning, neuroprotection against gp120 by moderate ethanol coexposure appears secondary to abrogation of the retroviral protein's early induction of arachidonic acid (AA), glutamate, and superoxide (but not nitric oxide) elevations/release. Additionally, experiments indicate that 30 mM ethanol is sufficient to inhibit the NMDA receptor, particularly in the presence of added glycine, thus hindering potential direct neuronal stimulation by gp120. However, in contrast to moderate ethanol, 100 mM ethanol, a concentration tolerated only in chronic alcoholics, potentiates gp120-dependent neurotoxicity (PI labeling) in the hippocampal CA1 region, augments LDH release, and fails to curtail gp120's actions on AA, glutamate, and superoxide-but does suppress nitric oxide induction. The results indicate dominant roles for AA, superoxide, and glutamate-mediated oxidative stress in gp120's neurotoxic mechanism, but perhaps a less important role for NMDA receptor stimulation, which would be constrained at both ethanol concentrations employed. We suggest that ethanol's concentration-dependent, two-edged sword behavior could alter the development of dementia in HIV-1-infected individuals during social consumption or abuse. Further studies are needed to elucidate the differing apparently glial effects of the two concentrations of ethanol.

Protection against gp120-induced neurotoxicity by an array of estrogenic steroids

gp120, the coat protein of HIV, can be neurotoxic and is thought to contribute to AIDS-related dementia complex. Such toxicity involves activation of glutamate receptors, mobilization of free cytosolic calcium, and generation of oxygen radicals. We have previously shown that the estrogen 17β-estradiol, in concentrations of 100 nM or higher, lessens the neurotoxicity of gp120 in hippocampal and cortical cultures, blunts gp120-induced calcium mobilization, and lessens the oxidative consequences. In this study, we examined the protective potential of other estrogens. We found gp120 neurotoxicity in hippocampal cultures to be significantly lessened by estrone, equilin and estriol, although with an order of magnitude less potent than 17β-estradiol. We also found all four estrogens to blunt gp120-induced calcium mobilization, with estriol being more efficacious than the other three estrogens. These findings give insight both into the mechanisms of estrogenic protection (e.g. receptor-dependent versus independent actions) as well as into the potential therapeutic use of estrogens against AIDS-related dementia complex.

Ethanol pre-exposure suppresses HIV-1 glycoprotein 120-induced neuronal degeneration by abrogating endogenous glutamate/Ca2+-mediated neurotoxicity.

The neurotoxic mechanism of HIV-1 envelope glycoprotein 120 (gp120) involves glutamatergic (NMDA) receptor/Ca2+-dependent excitotoxicity, mediated in part via glia. Pro-inflammatory cytokines also may have roles. We have reported that pre-exposure of brain cultures to 'physiological' ethanol concentrations (20-30 mM) protects against neuronal damage from HIV-1 gp120, but not from the direct receptor agonist, NMDA. Using lactate dehydrogenase assays and propidium iodide staining of rat organotypic hippocampal-entorhinal cortical slice cultures we determined that ethanol's suppression of gp120 neurotoxicity required at least 4 days of pretreatment. The gp120-induced neurotoxicity was accompanied by interleukin-6 elevations that were not affected by the pretreatment. However, gp120 induced substantial, early increases in extracellular glutamate levels that were blocked by ethanol pretreatment, conceivably abrogating excitotoxicity. Consistent with abrogation of excitotoxic pathways, fura-2 imaging showed selective deficits in gp120-dependent intracellular Ca2+ responses in ethanol-pretreated slices. Gp120 is believed to increase glutamate levels by both stimulating release and inhibiting (re)uptake. Results with a labeled glutamate analog, D-[3H]aspartate, revealed that gp120's inhibition of glutamate uptake, rather than its stimulation of release, was abolished after ethanol. Further studies indicated that two converging effects of ethanol pretreatment may underlie the abolishment of gp120-mediated glutamate uptake inhibition: (a) blockade of gp120-induced release (ostensibly from glia) of arachidonic acid, an inhibitor of astroglial glutamate reuptake, and (b) modest proliferation and activation of astroglia upon gp120 stimulation--which are likely to augment glutamate transporters. Thus, as with gp120 itself, glia and glutamate/arachidonic acid regulation appear to be important targets for ethanol. Since moderate ethanol consumption is as common among HIV-infected individuals as in the general population, this newly recognized neuroprotective (and apparently anti-excitotoxic) effect of ethanol withdrawal in vitro could be important, but it requires further study before its significance, if any, is understood.

Mechanisms of Estrogenic Protection against gp120-Induced Neurotoxicity

gp120, an HIV coat glycoprotein that may play a role in AIDS-related dementia complex (ADC), induces neuronal toxicity characterized by NMDA receptor activation, accumulation of intracellular calcium, and downstream degenerative events including generation of reactive oxygen species and lipid peroxidation. We have previously demonstrated estrogenic protection against gp120 neurotoxicity in primary hippocampal cultures. We here characterize the mechanism of protection by blocking the classical cytosolic estrogen receptors and by measuring oxidative end points including accumulation of extracellular superoxide and lipid peroxidation. Despite blocking ERα and ERβ with 1 μM tamoxifen, we do not see a decrease in the protection afforded by 100 nM 17 β-estradiol against 200 pM gp120. Additionally, 17α-estradiol, which does not activate estrogen receptors, protects to the same extent as 17β-estradiol. 17β-Estradiol does, however, decrease gp120-induced lipid peroxidation and accumulation of superoxide. Together the data suggest an antioxidant mechanism of estrogen protection that is independent of receptor binding.

Energy dependency of glucocorticoid exacerbation of gp120 neurotoxicity.

The HIV envelope glycoprotein, gp120, a well documented neurotoxin, may be involved in AIDS-related dementia complex. gp120 works through an NMDA receptor- and calcium-dependent mechanism to damage neurons. We have previously demonstrated that both natural and synthetic glucocorticoids (GCs) exacerbate gp120-induced neurotoxicity and calcium mobilization in hippocampal mixed cultures. GCs, steroid hormones secreted during stress, are now shown to work in conjunction with gp120 to decrease ATP levels and to work synergistically with gp120 to decrease the mitochondrial potential in hippocampal cultures. Furthermore, energy supplementation blocked the ability of GCs to worsen gp120's effects on neuronal survival and calcium mobilization. A GC-induced reduction in glucose transport in hippocampal neurons, as previously documented, may contribute to this energetic dependency. These results may have clinical significance, considering the common treatment of severe cases of Pneumocystis carinii pneumonia, typical of HIV infection, with large doses of synthetic GCs.

Antioxidants and dipyridamole inhibit HIV-1 gp120-induced free radical-based oxidative damage to human monocytoid cells.

Reactive oxygen species (ROS) may play an important role in HIV-1 pathogenesis and HIV-1 gp120-induced neurotoxicity. Our studies determined the extent to which gp120 increased ROS production in human monocytic U937 cells and the effectiveness of various agents, including dipyridamole (DPR), in blocking these responses. The thiobarbituric acid-reactive substances (TBARS) assay was used as a measure of recombinant gp120 (HIV-1[3B])-induced oxidative damage to U937 cells. As a control, TBARS production was measured using a hypoxanthine/xanthine superoxide generating system. There was gp120-induced oxidative damage in U937 cells with a concentration that produces 50% of maximal effect (apparent EC50 value) of 11 pM. Polyclonal antiserum to gp120 significantly (p < 0.05) inhibited gp120-induced oxidative damage. gp120-induced oxidative damage was significantly inhibited 81% (p < 0.01) by catalase/superoxide dismutase, 53% (p < 0.05) by (+/-)-alpha-tocopherol, 78% (p < 0.01) by desferrioxamine, and 82% (p < 0.01) by ethylene diamine tetraacetic acid (EDTA). These results indicate that gp120 is capable of promoting iron-based oxygen free radical damage to U937 cells. DPR potently (p < 0.05) inhibited both hypoxanthine/xanthine- and gp120-induced oxidative damage with concentrations that produce 50% inhibition (apparent IC50 values) of 1.3 microM for hypoxanthine/xanthine and 1.0 microM for gp120. Therapeutic intervention against ROS production may prevent HIV-1 neurotoxicity.

Endocrine modulation of the neurotoxicity of gp120: implications for AIDS-related dementia complex.

HIV infection often involves the development of AIDS-related dementia complex, a variety of neurologic, neuropsychologic, and neuropathologic impairments. A possible contributor to AIDS-related dementia complex is the HIV envelope glycoprotein gp120, which damages neurons via a complex glutamate receptor- and calcium-dependent cascade. We demonstrate an endocrine modulation of the deleterious effects of gp120 in primary hippocampal and cortical cultures. Specifically, we observe that gp120-induced calcium mobilization and neurotoxicity are exacerbated by glucocorticoids, the adrenal steroids secreted during stress. Importantly, this deleterious synergy can occur between gp120 and synthetic glucocorticoids (such as prednisone or dexamethasone) that are used clinically in high concentrations to treat severe cases of the Pneumocystis carinii pneumonia typical of HIV infection. Conversely, we also observe that estradiol protects neurons from the deleterious actions of gp120, reducing toxicity and calcium mobilization.

Inhibition of murine embryonic growth by human immunodeficiency virus envelope protein and its prevention by vasoactive intestinal peptide and activity-dependent neurotrophic factor.

Intrauterine growth retardation and neurodevelopmental handicaps are common among infants born to HIV-positive mothers and may be due to the actions of virions and/or maternally derived viral products. The viral envelope protein, gp120, is toxic to neurons, induces neuronal dystrophy, and retards behavioral development in neonatal rats. Vasoactive intestinal peptide, a neuropeptide regulator of early postimplantation embryonic growth, and the neuroprotective protein, activity-dependent neurotrophic factor, prevent gp120-induced neurotoxicity. Whole embryo culture of gestational day 9.5 mouse embryos was used to assess the effect of gp120 on growth. Embryos treated with gp120 exhibited a dose-dependent inhibition of growth. gp120-treated embryos (10(-8) M) grew 1.2 somites in the 6-h incubation period, compared with 3.9 somites by control embryos. Embryos treated with gp120 were significantly smaller in cross-sectional area and had significantly less DNA and protein than controls. Growth inhibition induced by gp120 was prevented by cotreatment with vasoactive intestinal peptide or activity-dependent neurotrophic factor. gp120 may play a role in the growth retardation and developmental delays experienced by infants born to HIV-positive mothers. Vasoactive intestinal peptide and related factors may provide a therapeutic strategy in preventing developmental deficits.

The Effects of the HIV-1 Envelope Protein gp120 on the Production of Nitric Oxide and Proinflammatory Cytokines in Mixed Glial Cell Cultures

Although the neurotoxicity induced by the HIV envelope protein, gp120, has been demonstrated to require the presence of glial cells (microglia/astrocytes), the mechanisms for the gp120-induced neurotoxicity are not well understood. Moreover, the neurotoxic potencies of gp120s obtained from various HIV isolates are different. Since nitric oxide (NO) and proinflammatory cytokines (TNF-α, IL-1, IL-6) produced by glial cells have been involved in the neuropathogenesis of various diseases, this study examined the effects of gp120 obtained from two strains, HIV-1IIIBand HIV-1SF2, of the HIV-1 virus on the production of NO, TNF-α, IL-1α, IL-1β, and IL-6 in murine primary mixed glial cell cultures. The glial cells exposed to HIV-1IIIBgp120 released NO, TNF-α, and IL-6 in a dose-dependent manner, whereas IL-1α and IL-1β were undetectable. The cells exposed to HIV-1SF2gp120 increased the release of IL-6 only. The gp120-induced effects were significantly enhanced by priming glial cells with IFN-γ. To investigate the cellular sources and mechanisms of the gp120-induced IL-6 production,in situhybridization with mRNA for IL-6 was performed in HIV-1IIIBgp120- or HIV-1SF2gp120-stimulated microglia-enriched or astrocyte-enriched cultures. HIV-1IIIBgp120 or HIV-1SF2gp120 induced the expression of IL-6 mRNA in both microglia-enriched and astrocyte-enriched cultures, indicating that both microglia and astrocytes produce IL-6, and that the transcriptional regulation is involved in the gp120-induced IL-6 production. Taken together, these results demonstrate that the production of NO, TNF-α, IL-1, or IL-6 from glial cells is differentially regulated by HIV-1IIIBgp120 and HIV-1SF2gp120. These results may provide insights into the roles of NO and proinflammatory cytokines in the neurotoxicity of gp120s and the neuropathology of different strains of HIV-1 viruses.

In VivoTrapping of Nitric Oxide in the Brain of Neonatal Rats Treated with the HIV-1 Envelope Protein gp 120: Protective Effects of α-Phenyl-tert-butylnitrone

AIDS dementia complex is a neurological syndrome characterized by cognitive deficits and motor and behavioral dysfunction. The HIV-I envelope glycoprotein gp 120 has been implicated in the development of ATDS dementia. This protein has been shown to be neurotoxic and to cause learning impairment and retardation of the development of complex motor behavior in rat neonates. Nitric oxide has been implicated in gp 120-induced neurotoxicity. In the present study, we report for the first timein vivoevidence for the formation of nitric oxide in the CNS as a result of multiple subcutaneous injections of gp 120 to neonatal rats. Nitric oxide was trapped in the brain of neonatal rats by N-methyl-D-glucamine dithiocarbamate-Fe and the nitric oxide content measured by electron paramagnetic resonance spectroscopy. The nitrone-based spin trap α-phenyl-tert-butylnitrone at 50 mg/kg was found to prevent gp 120-mediated nitric oxide formation and to also protect against gp 120-induced behavioral impairment.

HIV-1 gp120-induced neurotoxicity to midbrain dopamine cultures

HIV-1-associated cognitive/motor dysfunction is a frequent neurological complication of acquired immunodeficiency syndrome (AIDS) and has been termed AIDS dementia complex (ADC. The HIV-1 envelope glycoprotein gp120 has been implicated in producing brain injury associated with ADC. The purpose of the present study was to determine if gp120-induced neurotoxicity is associated with damage to dopaminergic systems. Exposure of rat midbrain dopamine cultures to gp120 for 3 days reduced the ability of dopaminergic cells to transport this amine and also resulted in a reduction in dopamine neuron process length while it did not alter either dopamine cell number or the total number of neuronal cells. These detrimental effects of gp120 were prevented by an NMDA receptor antagonist (MK-801) or by preincubation with anti-gp120 antibody. These results suggest that dopaminergic neuronal damage may contribute to the manifestations of AIDS dementia complex.

Protection against HIV-1 gp120-induced brain damage by neuronal expression of human amyloid precursor protein.

Expression of the HIV-1 envelope protein gp120 in brains of transgenic (tg) mice induces extensive neurodegeneration (Toggas, S. M., E. Masliah, E. M. Rockenstein, G. F. Rall, C. R. Abraham, and L. Mucke. 1994. Nature [Lond.]. 367:188-193.). To further analyze the pathogenesis of gp120-induced neurotoxicity and to assess the neuroprotective potential of human amyloid precursor proteins (hAPPs) in vivo, different hAPP isoforms were expressed in neurons of gp120/hAPP-bigenic mice: hAPP751, which contains a Kunitz-type protease inhibitor domain, or hAPP695, which lacks this domain. Bigenic mice overexpressing hAPP751 at moderate levels showed significantly less neuronal loss, synapto-dendritic degeneration, and gliosis than singly tg mice expressing gp120 alone. In contrast, higher levels of hAPP695 expression in bigenic mice failed to prevent gp120-induced brain damage. These data indicate that hAPP can exert important neuroprotective functions in vivo and that the efficiency of this protection may depend on the hAPP isoform expressed and/or on the level of neuronal hAPP expression. Hence, molecules that mimic beneficial APP activities may be useful in the prevention/treatment of HIV-1-associated nervous system damage and, perhaps, also of other types of neural injury.

Prevention of HIV coat protein (gp120) toxicity in cortical cell cultures by riluzole

Neurological complications observed in HIV-infected patients are very frequent. Neocortical lesions include reduced neuronal density due to neuronal degeneration. The HIV envelope protein gp120 has potent neurotoxic properties in cell cultures blocked either by NMDA antagonists or calcium channel antagonists. Moreover, human monocytoid cell lines infected by HIV release endogenous toxic factors with comparable cellular actions. We have analysed the effects of riluzole, a compound reducing the excitatory amino acid release on gp120-induced neurotoxicity in primary neuronal cultures. Riluzole, which blocks the release of glutamate and aspartate from nerve terminals, prevents (10 −7 M) the neuronal degeneration produced by 20 pM of gp120 in cortical cell cultures. This result could suggest that toxic factors produced by activated macrophages might increase glutamate release, and that this may be prevented by riluzole.

Tetrodotoxin blocks HIV coat protein (gp120) toxicity in primary neuronal cultures

HIV-I-associated cognitive/motor complex is a frequent neurological complication of the acquired immunodeficiency syndrome (AIDS). The pathogenesis of this syndrome implicates immunopathological and toxic events such as the production of cytokines. The HIV envelope glycoprotein gp120 seems also to play a major role in this process. Gp120 could produce a slow neuronal death probably via the release of neurotoxic factors by CNS macrophages/monocytes. NMDA antagonists and Ca 2+ channel blockers in vitro have a powerfull neuroprotective effect against gp120 neurotoxicity. The purpose of the present work is to determine wether gp120-induced neurotoxicity is associated with an abnormal neuronal depolarization induced by putative neurotoxins. We have compared in vitro the neuroprotective effects of Tetrodotoxin a Na + channel blocker, the Ca 2+ channel blocker nifedipine and the NMDA antagonist MK-801 in primary cortical neurons taken from embryonic rat and intoxicated with gp120. We observed comparable neuroprotective effects with the 3 precited compounds suggesting that gp120-induced neurotoxic factors act on Na + channels. NMDA receptors and Ca 2+ channels in a cascade of cellular events. We confirmed that the presence of macrophages is needed to trigger a marked gp120-induced neurotoxicity. These results underline the fact that depolarization is an important component of gp120 neurotoxicity in primary neuronal cultures.