The HIV-1 coat protein gp120 and some of its fragments potently activate native cerebral NMDA receptors mediating neuropeptide release

Presynaptic release-regulating NMDA receptors in isolated nerve terminals: A narrative review

The existence of presynaptic, release‐regulating NMDA receptors in the CNS has been long matter of discussion. Most of the reviews dedicated to support this conclusion have preferentially focussed on the results from electrophysiological studies, paying little or no attention to the data obtained with purified synaptosomes, even though this experimental approach has been recognized as providing reliable information concerning the presence and the role of presynaptic release‐regulating receptors in the CNS. To fill the gap, this review is dedicated to summarising the results from studies with synaptosomes published during the last 40 years, which support the existence of auto and hetero NMDA receptors controlling the release of transmitters such as glutamate, GABA, dopamine, noradrenaline, 5‐HT, acetylcholine and peptides, in the CNS of mammals. The review also deals with the results from immunochemical studies in isolated nerve endings that confirm the functional observations.

SARS-CoV-2 infection in patients with serious mental illness and possible benefits of prophylaxis with Memantine and Amantadine

Patients with serious mental illness are a high-risk category of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Patients with schizophrenia are not participatory and have increased mortality and morbidity, patients with dementia cannot be cared for while depression, anxiety, bipolar tubing are associated with low immune status. Social stress is amplified by social isolation, amplifying depression and the mechanisms of decreased immunity. Hygiene measures and prophylactic behavior are impossible to put into practice in conditions of chronic mental illness. In coronavirus disease 2019 (COVID-19), the risk for severe development is associated with the presence of comorbidities and immune system deficiency. Prothrombotic status, cytokine storm and alveolar destruction are mechanisms that aggravate the evolution of patients, especially in the context in which they have dysfunction of the autonomic system. The activity of proinflammatory cytokines is accentuated by hyperglutamatergia, which potentiates oxidative stress and triggers the mechanisms of neural apoptosis by stimulating microglial activation. Activation of M1-type microglia has an important role in pathogenesis of major psychiatric disorders, such as major depression, schizophrenia or bipolar disorder, and may associate hippocampal atrophy and disconnection of cognitive structures. Memantine and Amantadine, N-methyl-D-aspartate (NMDA) glutamate receptor inhibitors, have demonstrated, through their pharmacological profile, psychotropic effects but also antiviral properties. In the conditions of the COVID-19 pandemic, based on these arguments, we suggest that they can be associated with the therapy with the basic psychotropics, Memantine or Amantadine, for the control of neuropsychiatric symptoms but also as adjuvants with antiviral action.

The Role of the Spinal Wnt Signaling Pathway in HIV-Related Neuropathic Pain

Human immunodeficiency virus (HIV)-related neuropathic pain includes HIV-induced neuropathic pain (HNP) and antiretroviral therapy-induced neuropathic pain (ART-NP). A significant amount of evidence from the past few years has shown that the development of HIV-related neuropathic pain is closely related to the activation of the Wnt signaling pathway in the spinal cord. This review summarizes the function of the spinal Wnt signaling pathway in HIV-induced neuropathic pain, focusing on the role of the spinal Wnt signaling pathway in HNP, and provides a theoretical basis for further studies and the exploration of new target drugs.

Immuno-Pharmacological Characterization of Presynaptic GluN3A-Containing NMDA Autoreceptors: Relevance to Anti-NMDA Receptor Autoimmune Diseases

Mouse hippocampal glutamatergic nerve endings express presynaptic release-regulating NMDA autoreceptors (NMDARs). The presence of GluN1, GluN2A, GluN2B, and GluN3A subunits in hippocampal vesicular glutamate transporter type 1-positive synaptosomes was confirmed with confocal microscopy. GluN2C, GluN2D, and GluN3B immunopositivity was scarcely present. Incubation of synaptosomes with the anti-GluN1, the anti-GluN2A, the anti-GluN2B, or the anti-GluN3A antibody prevented the 30 μM NMDA/1 μM glycine-evoked [³H]D-aspartate ([³H]D-ASP) release. The NMDA/glycine-evoked [³H]D-ASP release was reduced by increasing the external protons, consistent with the participation of GluN1 subunits lacking the N1 cassette to the receptor assembly. The result also excludes the involvement of GluN1/GluN3A dimers into the NMDA-evoked overflow. Complement (1:300) released [³H]D-ASP in a dizocilpine-sensitive manner, suggesting the participation of a NMDAR-mediated component in the releasing activity. Accordingly, the complement-evoked glutamate overflow was reduced in anti-GluN-treated synaptosomes when compared to the control. We speculated that incubation with antibodies had favored the internalization of NMDA receptors. Indeed, a significant reduction of the GluN1 and GluN2B proteins in the plasma membranes of anti-GluN1 or anti-GluN2B antibody-treated synaptosomes emerged in biotinylation studies. Altogether, our findings confirm the existence of presynaptic GluN3A-containing release-regulating NMDARs in mouse hippocampal glutamatergic nerve endings. Furthermore, they unveil presynaptic alteration of the GluN subunit insertion in synaptosomal plasma membranes elicited by anti-GluN antibodies that might be relevant to the central alterations occurring in patients suffering from autoimmune anti-NMDA diseases.

Feline Immunodeficiency Virus Neuropathogenesis: A Model for HIV-Induced CNS Inflammation and Neurodegeneration

Feline Immunodeficiency virus (FIV), similar to its human analog human immunodeficiency virus (HIV), enters the central nervous system (CNS) soon after infection and establishes a protected viral reservoir. The ensuing inflammation and damage give rise to varying degrees of cognitive decline collectively known as HIV-associated neurocognitive disorders (HAND). Because of the similarities to HIV infection and disease, FIV has provided a useful model for both in vitro and in vivo studies of CNS infection, inflammation and pathology. This mini review summarizes insights gained from studies of early infection, immune cell trafficking, inflammation and the mechanisms of neuropathogenesis. Advances in our understanding of these processes have contributed to the development of therapeutic interventions designed to protect neurons and regulate inflammatory activity.

Presynaptic Release-Regulating mGlu1 Receptors in Central Nervous System

Group I metabotropic glutamate (mGlu) receptors consists of mGlu1 and mGlu5 receptor subtypes. These receptors are widely distributed in the central nervous system (CNS), where they preferentially mediate facilitatory signaling in neurones and glial cells, mainly by favoring phospholipase (PLC) translocation. Based on the literature so far available, group I Metabotropic glutamate receptors (mGluRs) are preferentially expressed at the postsynaptic side of chemical synapsis, where they participate in the progression of the chemical stimulus. Studies, however, have shown the presence of these receptors also at the presynaptic level, where they exert several functions, including the modulation of transmitter exocytosis. Presynaptic Group I mGluRs can be both autoreceptors regulating release of glutamate and heteroreceptors regulating the release of various transmitters, including GABA, dopamine, noradrenaline, and acetylcholine. While the existence of presynaptic release-regulating mGlu5 receptors is largely recognized, the possibility that mGlu1 receptors also are present at this level has been a matter of discussion for a long time. A large body of evidence published in the last decade, however, supports this notion. This review aims at revisiting the data from in vitro studies concerning the existence and the role of release-regulating mGlu1 receptors presynaptically located in nerve terminals isolated from selected regions of the CNS. The functional interaction linking mGlu5 and mGlu1 receptor subtypes at nerve terminals and their relative contributions as modulators of central transmission will also be discussed. We apologize in advance for omission in our coverage of the existing literature.

HIV-1 gp120Bal down-Regulates Phosphorylated NMDA Receptor Subunit 1 in Cortical Neurons via Activation of Glutamate and Chemokine Receptors

HIV-1 envelope glycoprotein gp120 (gp120) is a major virulence protein implicated in the pathogenesis of HIV-associated neurocognitive disorders (HAND). Although gp120 has been suggested to cause synaptic and neuronal injuries by disrupting NMDA receptor (NMDAR) function, the underlying mechanism is unclear. Here, we show that gp120Bal down-regulates the phosphorylation of the NMDAR subunit1 NR1 (at Ser896 and Ser897), which is essential for NMDAR function. This effect of gp120Bal is blocked by specific antagonists of both NMDA and AMPA receptors, indicating a critical role of synaptic activation. Furthermore, AMD3100 and maraviroc, antagonists of CCR5 and CXCR4 chemokine receptors, respectively, inhibit the effect of gp120Bal on NR1, suggesting that CXCR4 and CCR5 activation are involved. These findings may provide mechanistic insights into the synaptopathogenesis caused by HIV-1 infection.

HIV-1 Tat-induced changes in synaptically-driven network activity adapt during prolonged exposure

HIV-associated neurocognitive disorders (HAND) afflict approximately half of HIV-infected patients. The HIV-1 transactivator of transcription (Tat) protein is released by infected cells and contributes to the pathogenesis of HAND, but many of the underlying mechanisms remain poorly understood. Here we used fura-2-based Ca(2+) imaging and whole-cell patch-clamp recording to study the effects of Tat on the spontaneous synaptic activity that occurs in networked rat hippocampal neurons in culture. Tat triggered aberrant network activity that exhibited a decrease in the frequency of spontaneous action potential bursts and Ca(2+) spikes with a simultaneous increase in burst duration and Ca(2+) spike amplitude. These network changes were apparent after 4 h treatment with Tat and required the low-density lipoprotein receptor-related protein (LRP). Interestingly, Tat-induced changes in network activity adapted during 24 h exposure. The activity returned to control levels in the maintained presence of Tat for 24 h. These observations indicate that Tat causes aberrant network activity, which is dependent on LRP, and adapts following prolonged exposure. Changes in network excitability may contribute to Tat-induced neurotoxicity in vitro and seizure disorders in vivo. Adaptation of neural networks may be a neuroprotective response to the sustained presence of the neurotoxic protein Tat and could underlie the behavioral and electrophysiological changes observed in HAND.

Uncovering the role of defective HIV-1 in spreading viral infection

ABSTRACT 

Defective HIV-1 genomes populate blood cells of HIV-1 infected patients, especially during HAART treatment. They can express viral proteins which, if released, may induce bystander effects favoring viral spread. Here, we review recent literature regarding the effects of extracellular HIV-1 proteins which can act as effectors of transcriptionally active, defective HIV-1, including Gag p17, Env gp120, Vpr, Tat and Nef. It has been very recently described that, different to the other HIV products, the bystander effects of Nef can be mediated by exosomes, that is, nanovesicles constitutively released by all cell types. Exosomes from Nef-expressing cells induce cell activation and HIV-1 susceptibility in resting CD4+ T lymphocytes in a TNF-α-dependent way. This mechanism likely contributes to virus persistence in HAART-treated patients.

Wnt signaling in the pathogenesis of human HIV-associated pain syndromes

Many synaptic plasticity-related signaling pathways have been identified as important regulators of the pathogenesis of chronic pain in animal models. However, their relevance to human pathological pain is rarely confirmed rigorously. Recent studies suggest that Wnt signaling plays critical roles in synaptic plasticity and is dysregulated in the spinal cord dorsal horn (SDH) of different mouse pain models. In this study, we compared the protein levels of Wnt ligands, Wnt receptors and their downstream effector proteins in the SDH from non-HIV patients, HIV patients who developed chronic pain ('pain-positive' HIV patients), and HIV patients who did not develop chronic pain ('pain-negative' HIV patients). Our results indicate that many Wnt ligands and downstream effector proteins were specifically up-regulated in the SDH of 'pain-positive' HIV patients but not in the 'pain-negative' HIV patients. These findings describe an HIV pain-associated activation of Wnt signaling in the SDH of human patients. Given the established role of Wnt signaling in the regulation of synaptic plasticity, these results suggest that the activated Wnt signaling might contribute to the expression of the synaptic plasticity in the SDH during the pathogenesis of HIV-associated chronic pain.

Wingless-type mammary tumor virus integration site family, member 5A (Wnt5a) regulates human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein 120 (gp120)-induced expression of pro-inflammatory cytokines via the Ca2+/calmodulin-dependent protein kinase II (CaMKII) and c-Jun N-terminal kinase (JNK) signaling pathways

BACKGROUND

HIV-1 infection causes chronic neuroinflammation in the central nervous system (CNS).

RESULTS

The spinal cytokine up-regulation induced by HIV-1 gp120 protein depends on Wnt5a/CaMKII and/or Wnt5a/JNK pathways.

CONCLUSION

gp120 stimulates cytokine expression in the spinal cord dorsal horn by activating Wnt5a signaling.

SIGNIFICANCE

The finding reveals Wnt signaling-mediated novel mechanisms by which HIV-1 may cause neuroinflammation. Chronic expression of pro-inflammatory cytokines critically contributes to the pathogenesis of HIV-associated neurological disorders (HANDs), but the host mechanism that regulates the HIV-induced cytokine expression in the CNS remains elusive. Here, we present evidence for a crucial role of Wnt5a signaling in the expression of pro-inflammatory cytokines in the spinal cord induced by a major HIV-envelope protein, gp120. Wnt5a is mainly expressed in spinal neurons, and rapidly up-regulated by intrathecal injection (i.t.) of gp120. We show that inhibition of Wnt5a by specific antagonists blocks gp120-induced up-regulation of IL-1β, IL-6, and TNF-α in the spinal cord. Conversely, injection (i.t.) of purified recombinant Wnt5a stimulates the expression of these cytokines. To elucidate the role of the Wnt5a-regulated signaling pathways in gp120-induced cytokine expression, we have focused on CaMKII and JNKs, the well characterized down-stream targets of Wnt5a signaling. We find that Wnt5a is required for gp120 to activate CaMKII and JNK signaling. Furthermore, we demonstrate that the Wnt5a/CaMKII pathway is critical for the gp120-induced expression of IL-1β, whereas the Wnt5a/JNK pathway is for TNF-α expression. Meanwhile, the expression of IL-6 is co-regulated by both pathways. These results collectively suggest that Wnt5a signaling cascades play a crucial role in the regulation of gp120-induced expression of pro-inflammatory cytokines in the CNS.

Evidence of reduced glutamate in the frontal lobe of HIV-seropositive patients

Neurological complications associated with the acquired immunodeficiency syndrome, in particular, HIV-associated dementia, continue to plague those infected. We report our finding that the concentration of brain Glu is reduced in the frontal white matter region in this condition. In addition, our data appear to absolve highly active retroviral therapy (HAART) from blame, as drug-naïve patients were equally affected. Our findings suggest that Glu neurotransmission is abnormal and may be a key target for early interventions to reduce the later incidence of neurocognitive impairment and dementia among HIV-seropositive patients.

Presynaptic metabotropic glutamate and GABAB receptors

Glutamate and GABA, the two most abundant neurotransmitters in the mammalian central nervous system, can act on metabotropic receptors that are structurally quite dissimilar from those targeted by most other neurotransmitters/modulators. Accordingly, metabotropic glutamate receptors (mGluRs) and GABA(B) receptors (GABA(B)Rs) are classified as members of family 3 (or family C) of G protein-coupled receptors. On the other hand, mGluRs and GABA(B)Rs exhibit pronounced and partly unresolved differences between each other. The most intriguing difference is that mGluRs exist as multiple pharmacologically as well as structurally distinct subtypes, whereas, in the case of GABA(B)Rs, molecular biologists have so far identified only one structurally distinct heterodimeric complex whose few variants seem unable to explain the pharmacological heterogeneity of GABA(B)Rs observed in many functional studies. Both mGluRs and GABA(B)Rs can be localized on axon terminals of different neuronal systems as presynaptic autoreceptors and heteroreceptors modulating the exocytosis of various transmitters.

HIV-1 protein gp120 rapidly impairs memory in chicks by interrupting the glutamate–glutamine cycle

Learning and memory impairments are frequently observed in patients suffering from AIDS Dementia Complex (ADC). These effects have been linked to the presence of gp120, an HIV viral coat glycoprotein. The present study investigated the possibility that gp120 prevents the uptake of extracellular glutamate by astrocytes, leading to an interruption of the glutamate-glutamine cycle and a subsequent impairment of memory. Ten microliters of 10nM gp120 was bilaterally injected into the region of the intermediate medial mesopallium of day-old chicks at various times before, or after, training using a single-trial passive avoidance task. Gp120 was found to significantly impair memory retention when injected 10-40 min after training. Memory impairments were evident within 5 min of gp120 administration and remained evident 24h later. Further, the amnestic effect of gp120 could be overcome with glutamine or with precursors of glutamate synthesis, but only weakly by glutamate. These results support the conclusion that the amnestic effect of gp120 is due to an impaired uptake of glutamate by astrocytes and a subsequent interruption of glutamine supply to neurones. The data indicate that the glutamate-glutamine cycle may be a useful therapeutic target in the treatment of ADC.

Feline immunodeficiency virus neuropathogenesis: from cats to calcium

Invasion of human immunodeficiency virus (HIV) into the central and peripheral nervous system produces a wide range of neurological symptoms, which continue to persist even with adequate therapeutic suppression of the systemic viremia. The development of therapies designed to prevent the neurological complications of HIV require a detailed understanding of the mechanisms of virus penetration into the nervous system, infection, and subsequent neuropathogenesis. These processes, however, are difficult to study in humans. The identification of animal lentiviruses similar to HIV has provided useful models of HIV infection that have greatly facilitated these efforts. This review summarizes contributions made from in vitro and in vivo studies on the infectious and pathological interactions of feline immunodeficiency virus (FIV) with the nervous system. In vivo studies on FIV have provided insights into the natural progression of CNS disease as well as the contribution of various risk factors. In vitro studies have contributed to our understanding of immune cell trafficking, CNS infection and neuropathogenesis. Together, these studies have made unique contributions to our understanding of (1) lentiviral interactions at the blood-cerebrospinal fluid (CSF) barrier within the choroid plexus, (2) early FIV invasion and pathogenesis in the brain, and (3) lentiviral effects on intracellular calcium deregulation and neuronal dysfunction. The ability to combine in vitro and in vivo studies on FIV offers enormous potential to explore neuropathogenic mechanisms and generate information necessary for the development of effective therapeutic interventions.

Ethanol potentiates HIV-1 gp120-induced apoptosis in human neurons via both the death receptor and NMDA receptor pathways

Neuronal loss is a hallmark of AIDS dementia syndromes. Human immunodeficiency virus type I (HIV-1)-specific proteins may induce neuronal apoptosis, but the signal transduction of HIV-1 gp120-induced, direct neuronal apoptosis remains unclear. Ethanol (EtOH) is considered to be an environmental co-factor in AIDS development. However, whether EtOH abuse in patients with AIDS increases neuronal dysfunction is still uncertain. Using pure, differentiated, and post-mitotic NT2.N-derived human neurons, we investigated the mechanisms of HIV-1 and/or EtOH-related direct neuronal injury and the molecular interactions between HIV-1-specific proteins and EtOH. It was demonstrated that NT2.N neurons were susceptible to HIV-1 Bal (R5-tropic strain) gp120-induced direct cell death. Of importance, EtOH induced cell death in human neurons in a clinically-relevant dose range and EtOH strongly potentiated HIV-1 gp120-induced neuronal injury at low and moderate concentrations. Furthermore, this potentiation of neurotoxicity could be blocked by N-methyl-D-aspartate (NMDA) receptor subunit 2B (NR2B) antagonists. We analyzed human genomic profiles in these human neurons, using Affymetrix genomics technology, to elucidate the apoptotic pathways involved in HIV-1- and EtOH-related neurodegeneration. Our findings indicated significant over-expression of selected apoptosis functional genes. Significant up-regulation of TRAF5 gene expression may play an essential role in triggering potentiation by EtOH of HIV-1 gp120-induced neuronal apoptosis at early stages of interaction. These studies suggested that two primary apoptotic pathways, death receptor (extrinsic) and NMDA receptor (intrinsic)-related programmed cell-death pathways, are both involved in the potentiation by EtOH of HIV-1 gp120-induced direct human neuronal death. Thus, these data suggest rationally-designed, molecular targets for potential anti-HIV-1 neuroprotection.

The human immunodeficiency virus-1 protein Tat and its discrete fragments evoke selective release of acetylcholine from human and rat cerebrocortical terminals through species-specific mechanisms

The effect of the human immunodeficiency virus-1 protein Tat was investigated on neurotransmitter release from human and rat cortical nerve endings. Tat failed to affect the release of several neurotransmitters, such as glutamate, GABA, norepinephrine, and others, but it evoked the release of [3H]ACh via increase of cytosolic [Ca2+]. In human nerve terminals, the Tat effect partly depends on Ca2+ entry through voltage-sensitive Ca2+ channels, because Cd2+ halved the Tat-evoked release. Activation of group I metabotropic glutamate receptors (mGluR) and mobilization of Ca2+ from IP3-sensitive intraterminal stores are also involved, because the Tat effect was prevented by mGluR antagonists 2-methyl-6-(phenylethynyl)pyridine hydrochloride and 7-(hydroxyimino)cyclopropa[b]chromen-1a-carboxylate ethyl ester and by the IP3 receptor antagonists heparin and xestospongin C. Furthermore, the group I selective mGlu agonist (RS)-3,5-dihydroxyphenylglycine enhanced [3H]ACh release. In rat nerve terminals, the Tat-evoked release neither depends on external Ca2+ ions entry nor on IP3-mediated mechanisms. Tat seems to cause mobilization of Ca2+ from ryanodine-sensitive internal stores because its effect was prevented by both 8-bromo-cyclic adenosine diphosphate-ribose and dantrolene. The Tat-evoked release from human synaptosomes was mimicked by the peptide sequences Tat 32-62, Tat 49-86, and Tat 41-60. In contrast, the Tat 49-86 and Tat 61-80 fragments, but not the Tat 32-62 fragment, were active in rat synaptosomes. In conclusion, Tat elicits Ca2+-dependent [3H]ACh release by species-specific intraterminal mechanisms by binding via discrete amino acid sequences to different receptive sites on human and rat cholinergic terminals.

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.

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.