Death of cultured human neuroblastoma cells induced by HIV-1 gp120 is prevented by NMDA receptor antagonists and inhibitors of nitric oxide and cyclooxygenase

The role of catecholamines in HIV neuropathogenesis

The success of anti-retroviral therapy has improved the quality of life and lifespan of HIV + individuals, transforming HIV infection into a chronic condition. These improvements have come with a cost, as chronic HIV infection and long-term therapy have resulted in the emergence of a number of new pathologies. This includes a variety of the neuropathological and neurocognitive effects collectively known as HIVassociated neurocognitive disorders (HAND) or NeuroHIV. These effects persist even in the absence of viral replication, suggesting that they are mediated the long-term changes in the CNS induced by HIV infection rather than by active replication. Among these effects are significant changes in catecholaminergic neurotransmission, especially in dopaminergic brain regions. In HIV-infected individuals not treated with ARV show prominent neuropathology is common in dopamine-rich brain regions and altered autonomic nervous system activity. Even infected individuals on therapy, there is significant dopaminergic neuropathology, and elevated stress and norepinephrine levels correlate with a decreased effectiveness of antiretroviral drugs. As catecholamines function as immunomodulatory factors, the resultant dysregulation of catecholaminergic tone could substantially alter the development of HIVassociated neuroinflammation and neuropathology. In this review, we discuss the role of catecholamines in the etiology of HIV neuropathogenesis. Providing a comprehensive examination of what is known about these molecules in the context of HIV-associated disease demonstrates the importance of further studies in this area, and may open the door to new therapeutic strategies that specifically ameliorate the effects of catecholaminergic dysregulation on NeuroHIV.

Targeting the glutamatergic system for the treatment of HIV-associated neurocognitive disorders

The accumulation of excess glutamate in the extracellular space as a consequence of CNS trauma, neurodegenerative diseases, infection, or deregulation of glutamate clearance results in neuronal damage by excessive excitatory neurotransmission. Glutamate excitotoxicity is thought to be one of several mechanisms by which HIV exerts neurotoxicity that culminates in HIV-associated neurocognitive disorders (HAND). Excess glutamate is released upon HIV infection of macrophage/microglial cells and has been associated with neurotoxicity mediated by gp120, transactivator of transcription (Tat) and other HIV proteins. Several strategies have been used over the years to try to prevent glutamate excitotoxicity. Since the main toxic effects of excess glutamate are thought to be due to excitotoxicity from over activation of glutamate receptors, antagonists of these receptors have been popular therapeutic targets. Early work to ameliorate the effects of excess extracellular glutamate focused on NMDA receptor antagonism, but unfortunately, potent blockade of this receptor has been fraught with side effects. One alternative to direct receptor blockade has been the inhibition of enzymes responsible for the production of glutamate such as glutaminase and glutamate carboxypeptidase II. Another approach has been to regulate the transporters responsible for modulation of extracellular glutamate such as excitatory amino acid transporters and the glutamate-cystine antiporter. There is preliminary experimental evidence that these approaches have potential therapeutic utility for the treatment of HAND. These efforts however, are at an early stage where the next steps are dependent on the identification of drug-like inhibitors as well as the development of predictive neuroAIDS animal models.

Infectious agents and neurodegeneration

A growing body of epidemiologic and experimental data point to chronic bacterial and viral infections as possible risk factors for neurodegenerative diseases, including Alzheimer’s disease, Parkinson’s disease and amyotrophic lateral sclerosis. Infections of the central nervous system, especially those characterized by a chronic progressive course, may produce multiple damage in infected and neighbouring cells. The activation of inflammatory processes and host immune responses cause chronic damage resulting in alterations of neuronal function and viability, but different pathogens can also directly trigger neurotoxic pathways. Indeed, viral and microbial agents have been reported to produce molecular hallmarks of neurodegeneration, such as the production and deposit of misfolded protein aggregates, oxidative stress, deficient autophagic processes, synaptopathies and neuronal death. These effects may act in synergy with other recognized risk factors, such as aging, concomitant metabolic diseases and the host’s specific genetic signature. This review will focus on the contribution given to neurodegeneration by herpes simplex type-1, human immunodeficiency and influenza viruses, and by Chlamydia pneumoniae.

Caloric restriction: is mammalian life extension linked to p53?

Caloric restriction, that is limiting food intake, is recognized in mammals as the best characterized and most reproducible strategy for extending lifespan, retarding physiological aging and delaying the onset of age-associated diseases. The aim of this mini review is to argue that p53 is the connection in the abilities of both the Sirt-1 pathway and the TOR pathway to impact on longevity of cells and organisms. This novel, lifespan regulating function of p53 may be evolutionarily more ancient than its relatively recent role in apoptosis and tumour suppression, and is likely to provide many new insights into lifespan modulation.

The human immunodeficiency virus coat protein gp120 promotes forward trafficking and surface clustering of NMDA receptors in membrane microdomains

Infection by the human immunodeficiency virus (HIV) can result in debilitating neurological syndromes collectively known as HIV-associated neurocognitive disorders. Although the HIV coat protein gp120 has been identified as a potent neurotoxin that enhances NMDA receptor function, the exact mechanisms for this effect are not known. Here we provide evidence that gp120 activates two separate signaling pathways that converge to enhance NMDA-evoked calcium flux by clustering NMDA receptors in modified membrane microdomains. gp120 enlarged and stabilized the structure of lipid microdomains on dendrites by mechanisms that involved a redox-regulated translocation of a sphingomyelin hydrolase (neutral sphingomyelinase-2) to the plasma membrane. A concurrent pathway was activated that accelerated the forward traffic of NMDA receptors by a PKA-dependent phosphorylation of the NR1 C-terminal serine 897 (masks an ER retention signal), followed by a PKC-dependent phosphorylation of serine 896 (important for surface expression). NMDA receptors were preferentially targeted to synapses and clustered in modified membrane microdomains. In these conditions, NMDA receptors were unable to laterally disperse and did not internalize, even in response to strong agonist induction. Focal NMDA-evoked calcium bursts were enhanced by threefold in these regions. Inhibiting membrane modification or NR1 phosphorylation prevented gp120 from accelerating the surface localization of NMDA receptors. Disrupting the structure of membrane microdomains after gp120 treatments restored the ability of NMDA receptors to disperse and internalize. These findings demonstrate that gp120 contributes to synaptic dysfunction in the setting of HIV infection by interfering with NMDA receptor trafficking.

Sensitivity to electrical stimulation of human immunodeficiency virus type 1 and MAGIC-5 cells

To determine the sensitivities to low electrical potential of human immunodeficiency virus type 1 (HIV-1) and its target cells, HIV-1 and MAGIC-5 cells were directly stimulated with a constant direct current potential of 1.0 V (vs. Ag/AgCl). HIV-1 was incubated for 3 h at 37°C on a poly-L-lysine-coated indium-tin oxide electrode, and then stimulated by an electrical potential. MAGIC-5 cells were seeded onto the electrically stimulated HIV-1 and cultured for 3 days at 37°C. HIV-1-infected cells were measured by multinuclear activation via a galactosidase indicator assay. MAGIC-5 cells were also stimulated by an electrical potential of 1.0 V; cell damage, proliferation and apoptosis were evaluated by trypan blue staining, cell counting and in situ apoptosis detection, respectively. HIV-1 was found to be damaged to a greater extent by electrical stimulation than the cells. In particular, after application of a 1.0-V potential for 3 min, HIV-1_LAI and HIV-1_KMT infection were inhibited by about 90%, but changes in cell damage, proliferation and apoptosis were virtually undetectable. These results suggested that HIV-1 is significantly more susceptible to low electrical potential than cells. This finding could form the basis of a novel therapeutic strategy against HIV-1 infection.

Human immunodeficiency virus type 1 clade B and C gp120 differentially induce neurotoxin arachidonic acid in human astrocytes: implications for neuroAIDS

HIV-1 clades (subtypes) differentially contribute to the neuropathogenesis of HIV-associated dementia (HAD) in neuroAIDS. HIV-1 envelop protein, gp120, plays a major role in neuronal function. It is not well understood how these HIV-1 clades exert these neuropathogenic differences. The N-methyl-D: -aspartate (NMDA) receptor-reduced glutamine synthesis could lead to secretion of neurotoxins such as arachidonic acid (AA) which plays a significant role in the neuropathogenic mechanisms in neuroAIDS. We hypothesize that clade B and C gp120 proteins exert differential effects on human primary astrocytes by production of the neurotoxin arachidonic acid. Our results indicate that clade B gp120 significantly downregulated NMDA receptor gene and protein expression, and level of glutamine while increasing expression of prostaglandin E2 (PGE(2)) and thromboxane A2 receptor (TBXA(2) R) compared to HIV-1 clade C gp120 protein. Thus, our studies for the first time demonstrate that HIV-1 clade B-gp120 protein appears to induce higher levels of expression of the neuropathogenic molecule cyclooxygenase-2 (COX-2)-mediated arachidonic acid by-products, PGE(2), and TBXA(2) R compared to HIV-1 clade C gp120 protein. These studies suggest that HIV-1 clade B and C gp120 proteins may play a differential role in the neuropathogenesis of HAD in neuroAIDS.

p73: a multifunctional protein in neurobiology

p73, a transcription factor of the p53 family, plays a key role in many biological processes including neuronal development. Indeed, mice deficient for both TAp73 and ΔNp73 isoforms display neuronal pathologies, including hydrocephalus and hippocampal dysgenesis, with defects in the CA1-CA3 pyramidal cell layers and the dentate gyrus. TAp73 expression increases in parallel with neuronal differentiation and its ectopic expression induces neurite outgrowth and expression of neuronal markers in neuroblastoma cell lines and neural stem cells, suggesting that it has a pro-differentiation role. In contrast, ΔNp73 shows a survival function in mature cortical neurons as selective ΔNp73 null mice have reduced cortical thickness. Recent evidence has also suggested that p73 isoforms are deregulated in neurodegenerative pathologies such as Alzheimer’s disease, with abnormal tau phosphorylation. Thus, in addition to its increasingly accepted contribution to tumorigenesis, the p73 subfamily also plays a role in neuronal development and neurodegeneration.

Interactions of HIV and methamphetamine: cellular and molecular mechanisms of toxicity potentiation

Methamphetamine (METH) is a highly addictive psychostimulant drug, whose abuse has reached epidemic proportions worldwide. METH use is disproportionally represented among populations at high risks for developing HIV infection or who are already infected with the virus. Psychostimulant abuse has been reported to exacerbate the cognitive deficits and neurodegenerative abnormalities observed in HIV-positive patients. Thus, the purpose of the present paper is to review the clinical and basic observations that METH potentiates the adverse effects of HIV infection. An additional purpose is to provide a synthesis of the cellular and molecular mechanisms that might be responsible for the increased toxicity observed in co-morbid patients. The reviewed data indicate that METH and HIV proteins, including gp120, gp41, Tat, Vpr and Nef, converge on various caspase-dependent death pathways to cause neuronal apoptosis. The role of reactive microgliosis in METH- and in HIV-induced toxicity is also discussed.

Effect of electrical stimulation on human immunodeficiency virus type-1 infectivity

We examined the effects of electrical stimulation on HIV-1-adsorbed MAGIC-5 (MAGIC-5/HIV-1) cells and unadsorbed MAGIC-5 (MAGIC-5) cells. When MAGIC-5 cells were stimulated by a constant d.c. potential of 1.0 V (vs Ag/Agcl) immediately after HIV-1(LAI) infection, infectivity was more affected by electrical stimulation than by cell membrane damage. In particular, after application of potential at 1.0 V for 5 min, about 1% of the membranes of the MAGIC-5/HIV-1(LAI) cells were damaged, but the infectivities of both HIV-1(LAI) and HIV-1(NL43-luc) cells decreased about 37 and 44%, respectively (p < 0.05). After application of potential at 1.0 V for 5 min, the mean fluorescence intensities (MFIs) of highly reactive oxygen species (hROS) and nitric oxide (NO) in MAGIC-5/HIV-1(NL43-Luc) cells were significantly increased compared with that of unstimulated MAGIC-5/HIV-1(NL43-Luc) cells (p < 0.01). However, the MFIs of hROS and NO in MAGIC-5 cells were also increased, to the same level, by electrical stimulation for 5 min. These results suggest that HIV-1 adsorbed onto or invading cells is damaged by direct or indirect effects of electrical stimulation, resulting in a decrease in HIV-1 infectivity. It is also suggested that hROS and NO induced by electrical stimulation are important factors for inhibiting HIV-1 infection.

Involvement of the nitric oxide/protein kinase G pathway in polychlorinated biphenyl-induced cell death in SH-SY 5Y neuroblastoma cells

Polychlorinated biphenyls (PCB) are persistent environmental contaminants whose chronic exposure can affect nervous system development and function. The cellular and molecular mechanisms underlying neuronal damage are not yet clear. In the present study, we investigated whether nitric oxide (NO) could be involved in aroclor 1254 (A1254; a PCB mixture)-induced cytotoxicity in SH-SY5Y human neuroblastoma cells. Prolonged exposure (24 hr) to A1254 (10-100 microg/ml) caused a dose-dependent reduction of cell viability that was attenuated in the presence of a calcium entry blocker, gadolinum (Gd(3+)) at 10 microM, a concentration able to block voltage-sensitive calcium channels. In addition, A1254 caused an increase of cytosolic calcium that was dependent on extracellular calcium, as measured by fura-2 videomicroscopy. A1254-induced calcium rise may stimulate NO production through an activation of neuronal NOS (nNOS). Indeed, the concomitant addition of the selective nNOS inhibitor N(omega)-propyl-L-arginine (NPLA) and A1254 prevented cell injury, suggesting that NO production plays a major role in A1254-evoked cell injury. Furthermore, the exposure (14 hr) to A1254 (30 microg/ml) produced an up-regulation of the expression of beta isoform of nNOS. This up-regulation was calcium dependent and was accompanied by an enhancement of NO production as demonstrated by an increase of nitrite formation. Moreover, A1254-induced cell injury was prevented when KT 5823, a selective cGMP/PKG inhibitor, was added concomitantly to 30 microg/ml A1254. These results suggest that PCB-induced cell death in neuroblastoma cells is mediated by an activation of the cGMP/PKG pathway triggered by NO production.

17beta-estradiol protects SH-SY5Y Cells against HIV-1 gp120-induced cell death: evidence for a role of estrogen receptors

Despite the large body of experimental evidence demonstrating the neuroprotective properties of 17beta-estradiol (17beta-E2) both in vitro and in vivo experimental models of neuronal injury, the exact mechanisms implicated in neuroprotection have not been fully delineated. Some experimental evidence highlight a role for the antioxidant properties of 17beta-E2 in mediating protection against oxidative injury. Parallel to these, evidence also exist which point to alternative mechanisms involving estrogen receptors (ER). The HIV-1 coat protein, gp120, has been implicated in the progression of central nervous system damage caused by HIV-1 infection. The neurotoxic effects induced by gp120 are triggered via an excitotoxic mechanism of cell death which implicates alteration of calcium homeostasis, activation of calcium-dependent pathways, mitochondrial uncoupling and membrane lipid peroxidation. In the present study, we demonstrate that 17beta-E2 protects human SH-SY5Y neuroblastoma cells from cell death elicited by gp120. Tamoxifen and ICI 182,780, two ER antagonists, both antagonized 17beta-E2-mediated inhibition of cell death. Exposure of SH-SY5Y cells to gp120 for 30min caused a significant accumulation of intracellular reactive oxygen species (ROS) and this was abrogated by 17beta-E2; however, the ability of 17beta-E2 to counteract ROS generation induced by gp120 does not account for the reported prevention of cell death because ICI 182,780 failed to revert intracellular ROS reduction caused by 17beta-E2 though it was able to revert prevention of cell death. Furthermore, by using 17alpha-E2, the isomer unable to stimulate ER which, however, retains the antioxidant effects, we observed that a pre-treatment with 17alpha-E2 was effective in preventing gp120-induced accumulation of ROS but it failed to affect cell death caused by the viral protein. Collectively, these data demonstrate that neuroprotection afforded by 17beta-E2 is receptor-mediated and ROS scavenging effects may not be implicated.

Molecular mechanisms of HIV-1 associated neurodegeneration

Since identification of the human immunodeficiency virus-1 (HIV-1), numerous studies suggest a link between neurological impairments, in particular dementia, with acquired immunodeficiency syndrome (AIDS) with alarming occurrence worldwide. Approximately, 60% of HIV-infected people show some form of neurological impairment, and neuropathological changes are found in 90% of autopsied cases. Approximately 30% of untreated HIV-infected persons may develop dementia. The mechanisms behind these pathological changes are still not understood. Mounting data obtained by in vivo and in vitro experiments suggest that neuronal apoptosis is a major feature of HIV associated dementia (HAD), which can occur in the absence of direct infection of neurons. The major pathway of neuronal apoptosis occurs indirectly through release of neurotoxins by activated cells in the central nervous system (CNS) involving the induction of excitotoxicity and oxidative stress. In addition a direct mechanism induced by viral proteins in the pathogenesis of HAD may also play a role. This review focuses on the molecular mechanisms of HIV-associated dementia and possible therapeutic strategies.

Human immunodeficiency virus type 1 envelope glycoprotein 120 induces cyclooxygenase-2 expression in neuroblastoma cells through a nuclear factor-kappaB and activating protein-1 mediated mechanism

Induction of cyclooxygenase-2 (COX-2) in the brain of people infected with human immunodeficiency virus type 1 (HIV-1) has been proposed as a cause of cognitive impairment in AIDS dementia. Here, we have analyzed the molecular mechanism by which its induction takes place in neuroblastoma cells. The HIV-1 envelope protein gp120 was able to induce COX-2 mRNA and protein in several human neuroblastoma cell lines, which express CXCR4 and CCR5 but not CD4. Moreover, gp120 induces COX-2 promoter transcription. Sequential deletions of the promoter show that deletion of a distal nuclear factor-kappaB (NF-kappaB) site abrogated gp120-dependent transcription. More importantly, overexpression of NF-kappaB inhibitory subunit, IkappaBalpha, completely abrogated gp120-induced COX-2 activity. However, transfection of p65/relA NF-kappaB was not enough to induce COX-2 transcription, suggesting that NF-kappaB was necessary but not sufficient to control COX-2 transcription induced by gp120. In addition to NF-kappaB, activating protein-1 (AP-1) but not nuclear factor of activated T cells (NFAT)-dependent transcription was induced by gp120. Transfection of a dominant negative mutant c-Jun protein, TAM-67, efficiently blocked the induction of COX-2 promoter by gp120, confirming AP-1 requirement. Moreover, gp120 rapidly activates the c-Jun amino-terminal kinase (JNK) and p38 mitogen-activated protein kinase phosphorylation. The importance of NF-kappaB and AP-1 in COX-2 promoter and protein induction was corroborated by using pharmacological NF-kappaB, p38 and JNK inhibitors.

Permeability of the blood–brain barrier to HIV-1 Tat

Infection with human immunodeficiency virus-1 (HIV-1) is associated with dysfunctions of the central nervous system (CNS). HIV-1 induces its effects on the CNS by a variety of mechanisms, including by shedding the neurotoxic viral proteins such as gp120 and Tat. Both HIV-1 and gp120 have been shown to cross the blood-brain barrier (BBB). It is has not been determined, however, whether blood-borne Tat can cross the BBB. Here, we found that Tat crosses the BBB by a nonsaturable mechanism with a unidirectional influx rate of about 0.490 microl/g/min. About 0.126% of an intravenous dose of Tat enters each g of brain. Radioactively labeled albumin injected simultaneously did not cross the BBB. The hypothalamus, occipital cortex, and hippocampus were the regions of the brain most permeable to Tat. Nonsaturable brain-to-blood efflux also occurred, most likely with reabsorption into the blood of the cerebrospinal fluid. In conclusion, we found that Tat crossed the BBB bidirectionally. Such permeability could provide a mechanism by which Tat produced on one side of the BBB could affect neural or immune function on the other side.

Regulation of the apoptosis-necrosis switch

Execution of the apoptotic program involves a relatively limited number of pathways. According to a general view, these would converge to activate the caspase family of proteases. However, there is increasing evidence that apoptotic-like features can also be found when caspases are inhibited. Moreover, under pathological conditions, apoptosis and nonapoptotic death paradigms are often interwined, which suggest that, in vivo, cells may use diverging execution pathways. Molecular switches between apoptosis and necrosis include adenosine triphosphate-dependent steps in the activation of caspases or steps sensitive to reactive oxygen/nitrogen species. In turn, caspase activation can cause necrosis by promoting ion overload.

Inflammatory neurodegeneration mediated by nitric oxide, glutamate, and mitochondria

In inflammatory, infectious, ischemic, and neurodegenerative pathologies of the central nervous system (CNS) glia become "activated" by inflammatory mediators, and express new proteins such as the inducible isoform of nitric oxide synthase (iNOS). Although these activated glia have benefi- cial roles, in vitro they potently kill cocultured neurons, and there is increasing evidence that they contribute to pathology in vivo. Nitric oxide (NO) from iNOS appears to be a key mediator of such glial-induced neuronal death. The high sensitivity of neurons to NO is partly due to NO causing inhibition of respiration, rapid glutamate release from both astrocytes and neurons, and subsequent excitotoxic death of the neurons. NO is a potent inhibitor of mitochondrial respiration, due to reversible binding of NO to cytochrome oxidase in competition with oxygen, resulting in inhibition of energy production and sensitization to hypoxia. Activated astrocytes or microglia cause a potent inhibition of respiration in cocultured neurons due to glial NO inhibiting cytochrome oxidase within the neurons, resulting in ATP depletion and glutamate release. In some conditions, glutamate- induced neuronal death can itself be mediated by N-methyl-D-aspartate (NMDA)-receptor activation of the neuronal isoform of NO synthase (nNOS) causing mitochondrial damage. In addition NO can be converted to a number of reactive derivatives such as peroxynitrite, NO2, N2O3, and S-nitrosothiols that can kill cells in part by inhibiting mitochondrial respiration or activation of mitochondrial permeability transition, triggering neuronal apoptosis or necrosis.

The Tat antagonist neomycin B hexa-arginine conjugate inhibits gp-120-induced death of human neuroblastoma cells

Several patients with acquired immunodeficiency syndrome (AIDS) develop neurological complications, which are referred to as human immunodeficiency virus (HIV)-associated dementia (HAD). The HIV-1 coat glycoprotein gp-120 has been proposed as the major etiologic agent for neuronal loss reported postmortem in the brain of AIDS patients. Chemokine receptors may play a role in gp-120-triggered neurotoxicity, both in vitro and in vivo, thus being an intriguing target for developing therapeutic strategies aimed to prevent or reduce neuronal damage occurring during HIV infection. We have previously shown that human CHP100 neuroblastoma cells express CXCR4 and CCR5 chemokine receptors and that interaction between gp-120 and these receptors contributes to cytotoxicity elicited by the protein. Here, we examined the neuroprotective potential of neomycin B hexa-arginine conjugate (NeoR), a recently synthesized compound with anti-HIV activity. We found that gp-120-triggered death is significantly reduced by NeoR, and this protective effect seems related to the ability of NeoR to interact with CXCR4 receptors. The ability of NeoR to cross the blood-brain barrier, as demonstrated in mice by systemic administration of the fluorescein conjugate drug, makes this compound a powerful and attractive therapeutic agent.

Mechanisms of HIV type 1-induced cognitive impairment: evidence for hippocampal cholinergic involvement with overstimulation of the VIPergic system by the viral coat protein core

HIV-1 is associated with a neuroAIDS syndrome that includes cognitive impairment. Several components of HIV-1 are capable of affecting cognition, but which of these is the major mediator is unknown. We injected into the lateral cerebral ventricle of mice HIV-1 pseudoviruses expressing the full viral genome with or without the viral coat glycoproteins, gp120/gp41. Only virus possessing gp120/gp41 induced defects in memory as assessed in an active avoidance T-maze footshock paradigm. By itself, gp120 also induced impairments that were reversed by hippocampal cholinergic stimulation. Paradoxically, low doses of gp120 could improve memory. Such low-dose, paradoxic improvement is a characteristic of substances that impair memory by overstimulating pathways that normally sustain memory. Consistent with this, a low, but not a high, dose of gp120 reversed memory impairment induced by overstimulation of the VIPergic system, a memory-sustaining pathway. Further characterization showed that two strains of gp120 (SF and MN) were equally effective at improving memory and that, unlike other actions of gp120, glycation was not required. We conclude that (1) the predominant cognitive-impairing component of HIV-1 is its viral coat glycoproteins, (2) gp120 impairs memory by overstimulating pathways that normally sustain memory, (3) the cognitive effect of gp120 is mediated by its protein core, and (4) gp120 likely impairs memory by affecting the cholinergic/VIPergic system.

HIV-1 coat protein gp120 stimulates interleukin-1beta secretion from human neuroblastoma cells: evidence for a role in the mechanism of cell death

1. The role of the pro-inflammatory cytokine interleukin-1beta (IL-1beta) in the mechanism of cell death induced by the human immunodeficiency virus type 1 (HIV-1) recombinant coat glycoprotein, gp120 IIIB, has been studied in the human CHP100 neuroblastoma cell line maintained in culture. 2. Death of neuroblastoma cells typically elicited by 10 pM gp120 or by human recombinant IL-1beta (10 ng x ml(-1)) has been minimized by the antagonist of IL-1 receptor, i.e. IL-1ra (0.5 and 50 ng x ml(-1), respectively), an endogenous molecule that antagonizes most of the biological actions of IL-1beta, or by an antibody (5 and 50 ng x ml(-1)) which blocks the human IL-1 receptor type I (IL-1RI). 3. ELISA experiments have established that gp120 enhances immunoreactive IL-1beta levels in the culture medium and this is prevented by exposure to the IL-1 converting enzyme (ICE) inhibitor t-butoxycarbonyl-L-aspartic acid benzyl ester-chloromethylketone [Boc-Asp(OBzl)-CMK] used at a concentration (2.5 microM) which significantly (P<0.001) reduces cell death. 4. Death of CHP100 cells induced by gp120 is also prevented by acetyl-Tyr-Val-Ala-Asp-chloromethylketone (Ac-YVAD-CMK; 10-100 microM), a second inhibitor of ICE, supporting the concept that the viral protein stimulates the conversion of the 31 kDa pro-IL-1beta in to the 17 kDa mature cytokine which is then secreted to cause death. 5. In conclusion, our present data demonstrate that gp120 stimulates the secretion of IL-1beta which then triggers CHP100 neuroblastoma cell death via stimulation of IL-1 receptor type I.

Ethanol exposure inhibits the cytotoxic effect induced by gp120 in CHP100 human neuroblastoma cells

The aim of present study was to investigate the acute effects of ethanol on cytotoxicity induced by HIV-1 coat protein gp120 in CHP100 human neuroblastoma cell line. We demonstrate that ethanol, within a range of clinically relevant concentrations (15-90 mM) prevents cell death elicited by gp120 (10 pM) in a dose dependent manner. This protective action seems to be mediated by a reduction of free intracellular Ca(2+) levels because ethanol, at concentrations ranging from 0.1-0.5%, is able to decrease gp120-stimulated Ca(2+) uptake up to 24%. Furthermore, our data show an involvement of NO/cGMP messenger system pathway, because ethanol is also able to reduce gp120-stimulated NO release (up to 45%) and cyclic GMP accumulation (up to 73%). These findings suggest that the protective effect of ethanol against gp120-induced cytotoxicity in CHP100 cells underlies a Ca(2+)-activated, NO/cGMP-dependent mechanism.

Intrathecal HIV-1 envelope glycoprotein gp120 induces enhanced pain states mediated by spinal cord proinflammatory cytokines

Perispinal (intrathecal) injection of the human immunodeficiency virus-1 (HIV-1) envelope glycoprotein gp120 creates exaggerated pain states. Decreases in response thresholds to both heat stimuli (thermal hyperalgesia) and light tactile stimuli (mechanical allodynia) are rapidly induced after gp120 administration. gp120 is the portion of HIV-1 that binds to and activates microglia and astrocytes. These glial cells have been proposed to be key mediators of gp120-induced hyperalgesia and allodynia because these pain changes are blocked by drugs thought to affect glial function preferentially. The aim of the present series of studies was to determine whether gp120-induced pain changes involve proinflammatory cytokines [interleukin-1beta (IL-1) and tumor necrosis factor-alpha (TNF-alpha)], substances released from activated glia. IL-1 and TNF antagonists each prevented gp120-induced pain changes. Intrathecal gp120 produced time-dependent, site-specific increases in TNF and IL-1 protein release into lumbosacral CSF; parallel cytokine increases in lumbar dorsal spinal cord were also observed. Intrathecal administration of fluorocitrate (a glial metabolic inhibitor), TNF antagonist, and IL-1 antagonist each blocked gp120-induced increases in spinal IL-1 protein. These results support the concept that activated glia in dorsal spinal cord can create exaggerated pain states via the release of proinflammatory cytokines.

Apoptosis in neuroblastomas induced by interferon-gamma involves the CD95/CD95L pathway

BACKGROUND AND PROCEDURE

The CD95/CD95 ligand (CD95L) system is a key regulator of apoptosis. To evaluate a possible role of the CD95/CD95L system in human neuroblastoma (NB) cells, we investigated the constitutive and interferongamma (INFgamma)-induced expression of CD95 and CD95L, and CD95-mediated cell death in the SK-N-BE(2) cell line.

RESULTS

Modulation of CD95/CD95L expression and triggering of an autocrine apoptotic mechanism by IFNgamma suggest a potential role for INFgamma as a therapeutic agent for NB.

CONCLUSIONS

The evidence that retinoids induce apoptosis via tissue transglutaminase (tTG) and that N-methyl-D-aspartate (NMDA) and gp120 act through the nitric oxide synthase (NOS) activation pathway, indicates the existence of different molecular mechanisms of action, whose pharmacological exploitation might be used in an additive fashion.

gp120 induces cell death in human neuroblastoma cells through the CXCR4 and CCR5 chemokine receptors

To infect target cells, the human immunodeficiency virus (HIV) type I (HIV-1) must engage not only the well-known CD4 molecule, but it also requires one of several recently described coreceptors. In particular, the CXCR4 (LESTR/fusin) receptor allows fusion and entry of T-tropic strains of HIV, whereas CCR5 is the major coreceptor used by primary HIV-1 strains that infect macrophages and CD4(+) T-helper cells (M-tropic viruses). In addition, the alpha chemokine SDF1alpha and the beta chemokines MIP1alpha, MIP1beta, and RANTES, natural ligands of CXCR4 and CCR5, respectively, are potent soluble inhibitors of HIV infection by blocking the binding between the viral envelope glycoprotein gp120 and the coreceptors. Approximately two-thirds of individuals with acquired immunodeficiency syndrome (AIDS) show neurologic complications, which are referred to a syndrome called AIDS dementia complex or HIV-1-associated cognitive/motor complex. The HIV-1 coat glycoprotein gp120 has been proposed as the major etiologic agent for neuronal damage, mediating both direct and indirect effects on the CNS. Furthermore, recent findings showing the presence of chemokine receptors on the surface of different cell types resident in the CNS raise the possibility that the association of gp120 with these receptors may contribute to the pathogenesis of neurological dysfunction. Here, we address the possible role of alpha and beta chemokines in inhibiting gp120-mediated neurotoxicity using the human neuroblastoma CHP100 cell line as an experimental model. We have previously shown that, in CHP100 cells, picomolar concentrations of gp120 produce a significant increase in cell death, which seems to proceed through a Ca(2+) - and NMDA receptor-dependent cascade. In this study, we gained insight into the mechanism(s) of neurotoxicity elicited by the viral glycoprotein. We found that CHP100 cells constitutively express both CXCR4 and CCR5 receptors and that stimulation with phorbol 12-myristate 13-acetate down-regulates their expression, thus preventing gp120-induced cell death. Furthermore, all the natural ligands of these receptors exerted protective effects against gp120-mediated neuronal damage, although with different efficiencies. These findings, together with our previous reports, suggest that the neuronal injury observed in HIV-1 infection could be due to direct (or indirect) interactions between the viral protein gp120 and chemokine and/or NMDA receptors.

The early phase of apoptosis in human neuroblastoma CHP100 cells is characterized by lipoxygenase-dependent ultraweak light emission

Human neuroblastoma CHP100 cells were forced into apoptosis (programmed cell death, PCD) or necrosis by treatment with calcium chloride or sodium nitroprusside (a nitric oxide donor), respectively. Cellular luminescence, a marker of membrane lipid peroxidation, was increased by calcium but not by nitroprusside, and reached a maximum of 4-fold the control value 2 hours after treatment. The increase in luminescence was paralleled by increased 5-lipoxygenase (up to 250% of the control value) and decreased catalase (down to 50%) activity within the same time window. Consistently, incubation of CHP100 cells with inhibitors of 5-lipoxygenase (5,8,11,14-eicosatetraynoic acid and MK886) reduced light emission and PCD, whereas inhibition of catalase by 3-amino-1, 2,4-triazole enhanced both processes. Treatment of CHP100 cells with retinoic acid or cisplatin, unrelated PCD inducers reported to activate the lipoxygenase pathway, also gave enhanced light emission parallel to PCD increase. Altogether, these results suggest that cellular luminescence is an early marker of apoptotic, but not necrotic, program(s) involving generation of hydrogen peroxide and activation of 5-lipoxygenase.

Spreading depression induces expression of calcium-independent protein kinase C subspecies in ischaemia-sensitive cortical layers: regulation by N-methyl-D-aspartate receptors and glucocorticoids

Spreading depression is a wave of sustained depolarization challenging the energy metabolism of the cells without causing irreversible damage. In the ischaemic brain, sreading depression-like depolarization contributes to the evolution of ischaemia to infarction. The depolarization is propagated by activation of N-methyl-D-aspartate receptors, but changes in signal transduction downstream of the receptors are not known. Because protein phosphorylation is a general mechanism whereby most cellular processes are regulated, and inhibition of N-methyl-D-aspartate receptors or protein kinase C is neuroprotective, the expression of protein kinase C subspecies in spreading depression was examined. Cortical treatment with KCl induced an upregulation of protein kinase Cdelta and zeta messenger RNA at 4 and 8 h, whereas protein kinase Calpha, beta, gamma and epsilon did not show significant changes. The gene induction was the strongest in layers 2 and 3, and was followed by an increased number of protein kinase Cdelta-immunoreactive neurons. Protein kinase Cdelta and zeta inductions were inhibited by pretreatment with an N-methyl-D-aspartate receptor antagonist, dizocilpine maleate, which also blocked spreading depression propagation, and with dexamethasone, which acted without blocking the propagation. Quinacrine, a phospholipase A2 inhibitor, reduced only protein kinase C5 induction. In addition, N(G)(-nitro-L-arginine methyl ester, a nitric oxide synthase inhibitor, did not influence protein kinase Cdelta or zeta induction, whereas 6-nitro-7-sulphamoylbenzo[f]quinoxaline-2,3-dione, an alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate/kainate receptor antagonist, and the cyclo-oxygenase inhibitors indomethacin and diclophenac tended to increase gene expression. The data show that cortical spreading depression induces Ca2(+)-independent protein kinase C subspecies delta and zeta, but not Ca(2+)-dependent subspecies, through activation of N-methyl-D-aspartate receptors and phospholipase A2. Even though the signal pathway is similar to the induction described previously in ischaemia for genes implicated in delayed neuronal death, the gene inductions observed here are not necessarily pathogenetic, but may represent a general reaction to metabolic stress.

Toxicity of human THP-1 monocytic cells towards neuron-like cells is reduced by non-steroidal anti-inflammatory drugs (NSAIDs)

There is mounting evidence that inflammatory processes, including activation of microglia, are upregulated in Alzheimer's disease. The importance of this phenomenon is indicated by multiple epidemiological studies showing that patients taking non-steroidal anti-inflammatory drugs (NSAIDs) have a substantially reduced prevalence of Alzheimer's disease. The pharmacological actions of anti-inflammatory drugs in brain are still uncertain. As a step towards identifying key pharmacological targets, we developed a neurotoxicity assay based on the property of supernatant media from stimulated human monocytic THP-1 cells to cause human neuroblastoma cell death. Similar neurotoxicity was observed when postmortem human microglia were substituted for THP-1 cells, establishing the validity of the assay for simulating neurotoxicity in human brain. A combination of lipopolysaccharide and interferon-gamma was used to activate the THP-1 cells. NSAIDs were effective in inhibiting neurotoxicity by this assay, while steroidal anti-inflammatories and propentofylline had no effect. The neuroprotective potency of NSAIDs appeared to be unrelated to their selective ability to inhibit cyclooxygenase-1 (COX-1) or cyclooxygenase-2 (COX-2). It is suggested that inhibition of monocyte cytotoxicity might be responsible for the apparent beneficial effects of NSAIDs in Alzheimer's disease.

Anandamide activates human platelets through a pathway independent of the arachidonate cascade

Anandamide (arachidonoylethanolamide, AnNH) is shown to activate human platelets, a process which was not inhibited by acetylsalicylic acid (aspirin). Unlike AnNH, hydroperoxides generated thereof by lipoxygenase activity, and the congener (13-hydroxy)linoleoylethanolamide, were unable to activate platelets, though they counteracted AnNH-mediated stimulation. On the other hand, palmitoylethanolamide neither activated human platelets nor blocked the AnNH effects. AnNH inactivation by human platelets was afforded by a high-affinity transporter, which was activated by nitric oxide-donors up to 225% of the control. The internalized AnNH could thus be hydrolyzed by a fatty acid amide hydrolase (FAAH), characterized here for the first time.

The role of excitotoxicity in neurodegenerative disease: implications for therapy

Glutamic acid is the principal excitatory neurotransmitter in the mammalian central nervous system. Glutamic acid binds to a variety of excitatory amino acid receptors, which are ligand-gated ion channels. It is activation of these receptors that leads to depolarisation and neuronal excitation. In normal synaptic functioning, activation of excitatory amino acid receptors is transitory. However, if, for any reason, receptor activation becomes excessive or prolonged, the target neurones become damaged and eventually die. This process of neuronal death is called excitotoxicity and appears to involve sustained elevations of intracellular calcium levels. Impairment of neuronal energy metabolism may sensitise neurones to excitotoxic cell death. The principle of excitotoxicity has been well-established experimentally, both in in vitro systems and in vivo, following administration of excitatory amino acids into the nervous system. A role for excitotoxicity in the aetiology or progression of several human neurodegenerative diseases has been proposed, which has stimulated much research recently. This has led to the hope that compounds that interfere with glutamatergic neurotransmission may be of clinical benefit in treating such diseases. However, except in the case of a few very rare conditions, direct evidence for a pathogenic role for excitotoxicity in neurological disease is missing. Much attention has been directed at obtaining evidence for a role for excitotoxicity in the neurological sequelae of stroke, and there now seems to be little doubt that such a process is indeed a determining factor in the extent of the lesions observed. Several clinical trials have evaluated the potential of antiglutamate drugs to improve outcome following acute ischaemic stroke, but to date, the results of these have been disappointing. In amyotrophic lateral sclerosis, neurolathyrism, and human immunodeficiency virus dementia complex, several lines of circumstantial evidence suggest that excitotoxicity may contribute to the pathogenic process. An antiglutamate drug, riluzole, recently has been shown to provide some therapeutic benefit in the treatment of amyotrophic lateral sclerosis. Parkinson's disease and Huntington's disease are examples of neurodegenerative diseases where mitochondrial dysfunction may sensitise specific populations of neurones to excitotoxicity from synaptic glutamic acid. The first clinical trials aimed at providing neuroprotection with antiglutamate drugs are currently in progress for these two diseases.

Anandamide hydrolysis by human cells in culture and brain

Anandamide (arachidonylethanolamide; AnNH) has important neuromodulatory and immunomodulatory activities. This lipid is rapidly taken up and hydrolyzed to arachidonate and ethanolamine in many organisms. As yet, AnNH inactivation has not been studied in humans. Here, a human brain fatty-acid amide hydrolase (FAAH) has been characterized as a single protein of 67 kDa with a pI of 7.6, showing apparent Km and Vmax values for AnNH of 2.0 +/- 0.2 microM and 800 +/- 75 pmol.min-1.mg of protein-1, respectively. The optimum pH and temperature for AnNH hydrolysis were 9.0 and 37 degreesC, respectively, and the activation energy of the reaction was 43.5 +/- 4.5 kJ.mol-1. Hydro(pero)xides derived from AnNH or its linoleoyl analogues by lipoxygenase action were competitive inhibitors of human brain FAAH, with apparent Ki values in the low micromolar range. One of these compounds, linoleoylethanolamide is the first natural inhibitor (Ki = 9.0 +/- 0.9 microM) of FAAH as yet discovered. An FAAH activity sharing several biochemical properties with the human brain enzyme was demonstrated in human neuroblastoma CHP100 and lymphoma U937 cells. Both cell lines have a high affinity transporter for AnNH, which had apparent Km and Vmax values for AnNH of 0.20 +/- 0.02 microM and 30 +/- 3 pmol.min-1.mg of protein-1 (CHP100 cells) and 0.13 +/- 0.01 microM and 140 +/- 15 pmol.min-1.mg of protein-1 (U937 cells), respectively. The AnNH carrier of both cell lines was activated up to 170% of the control by nitric oxide.

The HIV envelope protein gp120 in the nervous system: interactions with nitric oxide, interleukin-1beta and nerve growth factor signalling, with pathological implications in vivo and in vitro

The neuronal loss often described at post-mortem in the brain neocortex of patients suffering from AIDS has been proposed to be responsible for the development of the AIDS dementia complex. Neuroinvasive strains of the HIV virus infect macrophages, microglial cells, and multinucleated giant cells, but not neurones. Processing of the virus by cells of the myelomonocytic lineage yields viral products known to initiate a complex network of events that may lead to the death of neurones and to the development of AIDS-associated neurological syndrome. The HIV-1 coat protein gp120, in particular, has been proposed as a likely etiologic agent of the described neuronal loss because it causes the death of neurones in culture. More recently, it has been shown that brain cortical cell death caused in rats by intracerebroventricular injection of gp120 occurs via apoptosis. This observation broadens our knowledge of the pathophysiology of the reported neuronal cell loss and opens a new avenue of experimental research for the development of novel therapeutic strategies for the treatment of patients suffering from AIDS-associated neurological syndrome.

Cytotoxic effect of HIV-1 coat glycoprotein gp120 on human neuroblastoma CHP100 cells involves activation of the arachidonate cascade

HIV type-1 (HIV-1) coat glycoprotein gp120 causes necrotic death in human neuroblastoma CHP100 cells. Here, we investigated the possible role of the arachidonate cascade and membrane peroxidation in gp120-induced cell necrosis. It is shown that gp120 increases the intracellular concentrations of prostaglandin E2 and leukotriene B4 by up-regulating the activity and expression of the arachidonate-metabolizing enzymes prostaglandin H synthase and 5-lipoxygenase respectively. Consistent with this observation, selective inhibitors of prostaglandin H synthase (i.e. indomethacin) and 5-lipoxygenase (i.e. MK886 and caffeic acid) protected CHP100 cells against gp120-induced necrosis. Treatment with gp120 also enhanced membrane lipid peroxidation and this may be implicated in the execution of cell damage. Interestingly, incubation with exogenous nitric oxide (NO) mimicked the effects of gp120 on necrotic death of CHP100 cells and activation of prostaglandin H synthase and 5-lipoxygenase. This suggests that NO might participate in the mechanism by which gp120 activates the arachidonate cascade.

Requirement for membrane lipid peroxidation in HIV-1 gp120-induced neuroblastoma cell death

The HIV-1 envelope protein gp120 engenders Ca(2+)-mediated, excitotoxic damage of rodent neuronal and human neuroblastoma cells in culture. Here we report that human CHP100 neuroblastoma cells undergo early peroxidation of membrane lipids following a brief exposure to gp120. This effect is prevented by preincubating cell cultures with the 21-aminosteroid U-74389G, an inhibitor of membrane lipid peroxidation, which also rescues neuroblastoma cultures from gp120-induced cell death; conversely, no protection from cell death is observed when the 21-aminosteroid is added to neuroblastoma cultures after the induction of membrane lipid peroxidation by gp120. These data indicate that membrane lipid peroxidation has a causative role in the expression of cell death produced by the viral protein.

Macrophage behavior associated with acute and chronic exposure to HIV GP120, morphine and anandamide: endothelial implications

We demonstrate that immediate exposure to gp120 (5 min; 0.1 microg/ml) results in a significant shift of the macrophage population to an amoeboid and motile category (P<0.01; 91.7+/-5.5 vs. a control value of 42.4+/-4.2) and prior exposure with anti-gp120 antagonizes this shift. Acute exposure of the macrophages to morphine (10(-6) M) or anandamide (10(-6) M) resulted in the cells rounding up (shape factors of 0.84 and 0.87 respectively) and becoming non-motile. The action is blocked by prior treatment with the specific antagonists naloxone and SR 141716A. Chronic exposure (6 h) of the cells to all three agents resulted in a random migration pattern. Further, all agents blocked chemotaxis induced by DAMA and IL-1. Observation of the cells behavior during chronic exposure revealed a sporadic activity pattern with gp120 whereas morphine and anandamide first induced a period of inactivity which is followed by a period of activity (chemokinesis). Recent work from our laboratory has demonstrated that both morphine and anandamide acutely stimulate constitutive macrophage nitric oxide (NO) release, which then induces macrophage rounding and inactivity. It was therefore of interest to examine their behavior by exposing macrophages to the NO-donor SNAP. In a concentration dependent manner SNAP exhibited the same behavioral actions as both substances of abuse. Given this, we next determined if macrophages exposed to gp120 would release NO. We demonstrated that NO was released only when exposed to morphine and anandamide not gp120. Thus. the chemokinetic inducing activities of these agents may be the basis for excitotoxin liberation in neural tissues and/or a higher viral load in various organ systems since cellular adherence and random migration are stimulated.

HIV-1 gp120-induced apoptosis in the rat neocortex involves enhanced expression of cyclo-oxygenase type 2 (COX-2)

The effect of subchronic intracerebroventricular (i.c.v.) injection of the human immunodeficiency virus type 1 (HIV-1) recombinant protein gp120 (100 ng, given daily for up to 7 consecutive days) on cyclooxygenase type 2 (COX-2) expression was studied by immunohistochemistry in the brain of adult rats. In comparison to control, bovine serum albumin (100 ng, given i.c.v. for up to 7 days) treated animals (n = 6), a single daily injection of the viral protein for 7 consecutive days enhanced the number of COX-2 immunoreactive cells in the brain cortex of rats (n = 6 per group) and this was accompanied by a 50% increase over control PGE2 content in whole brain tissue homogenates (n = 6). In another series of experiments, pretreatment of rats (n = 6) with indomethacin (6.0 mg/kg given i.p. 1 h before gp120 injection), an inhibitor COX activity, prevented apoptotic death typically produced by gp120 in the neocortex of rat suggesting that enhancement of COX-2 expression may be involved in the mechanisms of apoptosis yielded by the HIV-1 coat protein.

Densitometric quantification of neuronal viability by computerized image analysis

A new method is presented for the quantification of cell viability based on densitometry with computerized image analysis. Neuronal cells were stained with crystal violet and densitometric analysis was performed with an IBAS 2.0 image analyzer (Kontron/ Zeiss), using specially implemented dedicated software which integrates the optical density of the culture in each well with the area covered by the stained cells. To test the reliability of the densitometric method cortical cells were plated at different concentrations (5 x 10(4)-10(6)/ml); the standard curve obtained by analysis of crystal violet staining showed a linear proportion between cell number and optical density signal. The validation and accuracy of the method were assessed and compared with other methods using rat cortical cells cultured in vitro for 10 days and exposed to kainic acid (250 microM) for 24 h. Neuronal viability was reduced by 40-50% and comparison with direct cell counting, MTT assay, and spectrophotometric analysis confirmed that the method is simple, quick, and reliable.

The human immunodeficiency virus type 1 (HIV-1) glycoprotein gp120 reduces the expression of neuronal nitric oxide synthase in the hippocampus but not in the cerebral cortex and medial septal nucleus of rat

The expression of neuronal type of nitric oxide synthase (nNOS) has been studied by immunocytochemistry in the brain of rats receiving a single daily (for up to 14 consecutive days) intracerebroventricular (i.c.v.) injection of the HIV-1 recombinant protein gp 120 (100 ng/day). This treatment failed to affect nNOS expression in the cerebral cortex and medial septal nucleus whereas it reduced nNOS immunopositive neurones in the CA1 hippocampal cell layer of rats treated with gp120 for 14 days; the latter effect was accompanied by a parallel decrease in Ca(2+)-dependent NOS enzyme activity in hippocampal brain tissue homogenates. In conclusion, the present data demonstrate that in rats gp120 reduces the expression of nNOS in the hippocampus, an area of the brain involved in memory formation.

gp120, a human immunodeficiency virus-1 coat protein, augments excitotoxic hippocampal injury in perinatal rats

Recent data suggest that gp120, a human immunodeficiency virus-1 (HIV-1) coat glycoprotein that is secreted by HIV-infected cells, is neurotoxic, and that this toxicity is mediated, at least in part, by activation of N-methyl-D-aspartate-type excitatory amino acid receptors. To test this hypothesis in vivo, we examined the neurotoxicity of gp120 injected intrahippocampally, alone or co-injected with the selective excitatory amino acid agonist N-methyl-D-aspartate, in seven-day-old rats. Severity of injury in the lesioned hippocampus was assessed five days later, using three outcome measures: histopathology, hippocampal atrophy (derived from regional cross-sectional area measurements) and loss of [3H]glutamate receptor binding (based on in vitro autoradiography assays). To confirm that any observed effects were attributable to gp120 bioactivity, each group of experiments included controls that received equal amounts of heat-treated gp120. Gp120 (200 ng) elicited minimal focal pyramidal cell loss immediately adjacent to the injection track; there was no hippocampal atrophy or loss of [3H]glutamate binding. Co-injection of 50 ng gp120 with N-methyl-D-aspartate (5 nmol, threshold excitotoxic dose) increased the severity of hippocampal injury; hippocampal atrophy was greater in animals that received injections of 5 nmol N-methyl-D-aspartate in combination with 50 ng gp120 than in those that received either N-methyl-D-aspartate alone (5 nmol) or 5 nmol N-methyl-D-aspartate+50 ng heat-treated gp120 (mean+/-S.E.M. percentage reduction in injected hippocampal volume vs contralateral: N-methyl-D-aspartate, -19+/-3; N-methyl-D-aspartate+gp120, -26.8+/-2.1; N-methyl-D-aspartate+heat-treated gp120, -14.0+/-2.2; P<0.001, ANOVA). Treatment with the competitive N-methyl-D-aspartate antagonist 3-((RS)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (20mg/kg) markedly reduced the severity of injury elicited by the combination of gp120 with N-methyl-D-aspartate. These data support the hypothesis that locally secreted gp120 could exert neurotoxic effects, mediated by N-methyl-D-aspartate receptor activation, in vivo in the immature brain.