Amelioration of neurotoxic effects of HIV envelope protein gp120 by fibroblast growth factor: a strategy for neuroprotection

Approximately two thirds of patients with human immunodeficiency virus encephalitis (HIVE) show cognitive impairment and neurodegeneration, while one third are cognitively unimpaired and their neuronal populations are preserved. Thus, it is possible that these individuals might have the capacity to produce neurotrophic factors capable of protecting neurons against the deleterious effects of HIV. In this context, the main objective of this study was to determine whether fibroblast growth factor 1 (FGF1) is protective against HIV. For this purpose levels of FGF1 immunoreactivity were determined in the frontal cortex of 35 AIDS cases subdivided into 4 groups according to the presence or absence of HIVE and neurodegeneration. In cases without both HIVE and neurodegeneration, mild to moderate levels of FGFI immunoreactivity were observed in pyramidal neurons, while in cases with HIVE but without neurodegeneration, levels were significiantly elevated. In contrast, individuals with both HIVE and neurodegeneration showed low levels of neuronal FGF1 immunoreactivity. Furthermore, studies in primary human neuronal cultures treated with the HIV envelope protein-gp120 in the presence or absence of FGF1 showed that FGF1 was protective against gpl20 neurotoxicity in a dose-dependent manner. Taken together, these results support the notion that upregulation of certain neurotrophic factors, such as FGF1, might protect the central nervous system from the neurotoxic effects of HIV.     

M‐tropic HIV envelope protein gp120 exhibits a different neuropathological profile than T‐tropic gp120 in rat striatum

Most early human immunodeficiency virus type 1 (HIV‐1) strains are macrophage (M)‐tropic HIV variants and use the chemokine receptor CCR5 for infection. Neuronal loss and dementia are less severe among individuals infected with M‐tropic strains. However, after several years, the T‐cell (T)‐tropic HIV strain, which uses the CXCR4 variant, can emerge in conjunction with brain abnormalities, suggesting strain‐specific differences in neuropathogenicity. The molecular and cellular mechanisms of such diversity remain under investigation. We have previously demonstrated that HIV envelope protein gp120IIIB, which binds to CXCR4, causes neuronal apoptosis in rodents. Thus, we have used a similar experimental model to examine the neurotoxic effects of M‐tropic gp120BaL. gp120BaL was microinjected in the rat striatum and neuronal apoptosis was examined in the striatum, as well as in anatomically connected areas, such as the somatosensory cortex and the substantia nigra. gp120BaL promoted neuronal apoptosis and tissue loss that were confined to the striatum. Apoptosis was associated with microglial activation and increased levels of interleukin‐1β. Intriguingly, gp120BaL increased brain‐derived neurotrophic factor in the striatum. Overall, our data show that gp120BaL demonstrates a different neuropathological profile than gp120IIIB. A better understanding of the pathogenic mechanisms mediating HIV neurotoxicity is vital for developing effective neuroprotective therapies against AIDS‐associated dementia complex.     

Learning impairment following intracerebral administration of the HIV envelope protein gp120 or a VIP antagonist

The external envelope glycoprotein (gp120) of the human immunodeficeincy virus (HIV) has been shown to be toxic to neurons in culture. To further investigate the neurological effects of gp120, the involvement of this protein with the acquisition of spatial discrimination was assessed. Both native and recombinant gp120 were administered into the cerebral ventricles of adult rats and performance was evaluated in the Morris swim maze. Gp120 treatment retarded acquisition after daily administration of 12 ng. The specificity of this impairment was demonstrated in that the performance of animals given the same amount of gp160 from recombinant baculovirus was not different from animals given saline. Vasoactive intestinal peptide (VIP) has been shown to block gp120-induced neurotoxicity in culture and a VIP receptor antagonist has displayed toxic properties to neurons in culture. We show here that this antagonist, which competitively inhibits VIP binding and blocks VIP-mediated functions in cell cultures from the CNS, also produced an impairment of performance. This retardation was attenuated by cotreatment with VIP, supporting the specificity of the observed impairment. Thus, gp120 and the VIP antagonist produced similar retardation of spatial discrimination, suggesting that both may impair memory for spatially related stimulus control.     

Peripheral nerve exposure to HIV viral envelope protein gp120 induces neuropathic pain and spinal gliosis

Painful sensory neuropathy is a common and debilitating consequence of human immunodeficiency virus (HIV). The underlying causes of neuropathic pain are most likely not due to direct infection of the nervous system by active virus. The goal of this study was to determine whether epineural exposure to the HIV-1 envelope protein gp120 could lead to chronic painful peripheral neuropathy. Two doses of gp120 or BSA control were transiently delivered epineurally via oxidized cellulose wrapped around the rat sciatic nerve. Animals were assessed for neuropathic pain behaviors at several intervals from 1-30 days following nerve surgery. Allodynia and hyperalgesia were observed within 1-3 days following gp120 and sustained throughout the testing period. The gp120-exposed sciatic nerve exhibited early but transient pathology, notably axonal swelling and increased tumor necrosis factor alpha (TNF-alpha) within the nerve trunk. In contrast, intense astrocytic and microglial activation was observed in the spinal cord, and this gliosis persisted for at least 30 days following epineural gp120, in parallel with neuropathic pain behaviors. These findings demonstrate that limited peripheral nerve exposure to HIV protein can induce persistent painful sensory neuropathy that may be sustained and magnified by long-term spinal neuropathology.     

Interleukin-6 mediates low-threshold mechanical allodynia induced by intrathecal HIV-1 envelope glycoprotein gp120

Spinal cord glia (microglia and astrocytes) contribute to enhanced pain states. One model that has been used to study this phenomenon is intrathecal (i.t.) administration of gp120, an envelope glycoprotein of HIV-1 known to activate spinal cord glia and thereby induce low-threshold mechanical allodynia, a pain symptom where normally innocuous (non-painful) stimuli are perceived as painful. Previous studies have shown that i.t. gp120-induced allodynia is mediated via the release of the glial pro-inflammatory cytokines, tumor necrosis factor-alpha (TNF), and interleukin-1beta (IL-1). As we have recently reported that i.t. gp120 induces the release of interleukin-6 (IL-6), in addition to IL-1 and TNF, the present study tested whether this IL-6 release in spinal cord contributes to gp120-induced mechanical allodynia and/or to gp120-induced increases in TNF and IL-1. An i.t. anti-rat IL-6 neutralizing antibody was used to block IL-6 actions upon its release by i.t. gp120. This IL-6 blockade abolished gp120-induced mechanical allodynia. While the literature predominantly documents the cascade of pro-inflammatory cytokines as beginning with TNF, followed by the stimulation of IL-1, and finally TNF plus IL-1 stimulating the release of IL-6, the present findings indicate that a blockade of IL-6 inhibits the gp120-induced elevations of TNF, IL-1, and IL-6 mRNA in dorsal spinal cord, elevation of IL-1 protein in lumbar dorsal spinal cord, and TNF and IL-1 protein release into the surrounding lumbosacral cerebrospinal fluid. These results would suggest that IL-6 induces pain facilitation, and may do so in part by stimulating the production and release of other pro-inflammatory cytokines.     

17beta-estradiol reduces neuronal apoptosis induced by HIV-1 gp120 in the neocortex of rat

The human immunodeficiency virus type 1 (HIV-1) coat glycoprotein gp120 represents a likely contributor to the development of HIV-1 associated dementia (HAD), a neurological syndrome often observed in AIDS patients and characterised by significant neuronal loss in the neocortex. Since recent studies have highlighted that female sex hormones represent potential neuroprotective agents against damage produced by acute and chronic injuries in the adult brain, we have investigated whether estrogens exert protection in a rat model of gp120 neurotoxicity. Our results demonstrate that systemic administration of 17beta-estradiol (E2, 0.02-0.2 mg/kg) significantly reduces apoptotic cell death observed in the neocortex of rat following subchronic i.c.v. administration of gp120 (100 ng/rat/day). Furthermore, both tamoxifen and ICI182,780, two selective antagonists of estrogen receptors (ER) in the brain, reverted the neuroprotective effect of E2. The molecular mechanism of estrogenic neuroprotection does not appear to involve modulation of the antiapoptotic Bcl-2 or the proapoptotic Bax since we failed to observe changes in the levels of the two proteins in the neocortical tissue after gp120 and/or E2 treatment. However, we detected increased levels of IL-1beta in the neocortex of rats injected with gp120, as early as 6h after drug administration, and this effect was potentiated following pretreatment with E2. Taken together, our results demonstrate that E2 exerts neuroprotection against gp120 neurotoxicity in vivo through a mechanism involving ER activation and, possibly, via modulation of neocortical levels of IL-1beta.     

Retrograde and anterograde transport of HIV protein gp120 in the nervous system

Neurodegeneration and gliosis are prominent pathological features of subjects with human immunodeficiency virus (HIV) dementia complex (HAD). In these patients, neurodegeneration occurs in uninfected neurons. In addition, these patients develop sensory neuropathy despite the antiretroviral therapy. The HIV protein gp120, which mimics some of the pathological alterations seen in HAD, is retrogradely transported in rodent neurons. However, it is still unclear whether gp120 can also be transported anterogradely and whether axonal transport can occur in the peripheral nervous system (PNS). To determine whether gp120 is transported retrogradely and/or anterogradely, we injected gp120IIIB together with the retrograde tracer fluoro-ruby (FR) or the anterograde tracer 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyamine perchlorate (DiI) into the rat superior colliculi. We discovered that gp120 is retrogradely transported with FR along a direct pathway from the superior colliculus to the retina and anterogradely transported with DiI to several areas of the occipital cortex. To determine whether gp120 is also axonally transported in the peripheral nerves, gp120 and FR were injected into the sciatic nerve. No gp120 immunoreactivity was found in the sciatic nerve or dorsal root ganglia, suggesting that gp120 axonal transport does not occur in the PNS. Gp120 axonal transport may play a role in neuronal injury. Therefore, we examined apoptosis at various time points after gp120 injection. Activated caspase-3 was evident within neurons transporting gp120. These results indicate that axonal transport of gp120 might exacerbate the pathogenesis of HIV-1.     

Suppression of PrP(Sc)- and HIV-1 gp120 induced neuronal cell death by sulfated colominic acid.

The scrapie prion protein (PrP(Sc)) has been shown to induce apoptosis of rat cortical neurons in vitro. Here we demonstrate that the toxic effect displayed by PrP(Sc) can be blocked by sulfated colominic acid (polymer of N-acetylneuraminic acid). This compound acts neuroprotectively at a concentration of > or = 0.3 microg/ml when preincubated with the neurons or PrP(Sc). Rat cortical cells also undergo apoptosis after incubation with the HIV-1 coat protein gpl20 in vitro. This effect was abolished also by sulfated colominic acid when preincubated with the cells or gpl20. Addition of 0.3 microg/ml of compound resulted in an increase in cell viability by about 1.6-1.9-fold compared to cultures incubated for 18 h with 30 ng/ml of PrP(Sc) or 20 ng/ml of gpl20 alone (containing about 40% viable cells). Sulfated colominic acid does not act as antagonist of NMDA receptor channels at concentrations of up to 3 microg/ml when co-administered with 100 microg/ml of NMDA. It displayed a strong cytoprotective effect on human T lymphoblastoid CEM cells exposed to HIV-1; a 50% protection occurred after preincubation of the cells with 0.43 microg/ml of compound. At the same concentration, the compound caused an inhibition of HIV-1-induced syncytium formation. Sulfated colominic acid may be a promising compound for treatment of dementia caused by PrP(Sc) and HIV-1 infections.     

Human immunodeficiency virus type 1 protein gp120 causes neuronal cell death in the rat brain by activating caspases

Human immunodeficiency virus type 1 (HIV-1) infection of the central nervous system is associated with microglia activation and neuronal apoptosis, alterations that are also caused by the HIV-1 envelope glycoprotein 120 (gp120) alone. This study was undertaken to examine the onset of gp120 neurotoxicity, the type of cell death and which cells of the adult rat brain are more sensitive to the toxic action of gp120. Gp120 or vehicle were injected chronically (daily for 3 or 7 days) into the lateral ventricle. Magnetic resonance imaging revealed hypertensive areas in the cortical and hippocampal gray matter in gp120-treated rats 7-10 days after the first injection, suggesting vasogenic edema. This phenomenon was accompanied by an enlargement of the lateral and third ventricles. Immunohistochemical analyses were then carried out to examine the toxic effect of gp120 at a cellular level. Several markers of apoptosis, including activated caspase-3 were observed at both 3 and 7 days throughout brains of gp120-treated rats, especially in the cerebral cortex. In this area, most of the apoptotic cells exhibited a pyramidal shape and were Nissl positive, indicative of neurons. Few non-neuronal cells exhibited signs of apoptosis. The results of the present study support the notion that gp120 is neurotoxic in vivo and provide evidence that gp120 activates a caspase-dependent apoptotic pathway.     

Human Immunodeficiency virus type 1 protein gp120 causes neuronal cell death in the rat brain by activating caspases

Human immunodeficiency virus type 1 (HIV-1) infection of the central nervous system is associated with microglia activation and neuronal apoptosis, alterations that are also caused by the HIV-1 envelope glycoprotein 120 (gp120) alone. This study was undertaken to examine the onset of gp120 neurotoxicity, the type of cell death and which cells of the adult rat brain are more sensitive to the toxic action of gp120. Gp120 or vehicle were injected chronically (daily for 3 or 7 days) into the lateral ventricle. Magnetic resonance imaging revealed hypertensive areas in the cortical and hippocampal gray matter in gp120-treated rats 7–10 days after the first injection, suggesting vasogenic edema. This phenomenon was accompanied by an enlargement of the lateral and third ventricles. Immunohistochemical analyses were then carried out to examine the toxic effect of gp120 at a cellular level. Several markers of apoptosis, including activated caspase-3 were observed at both 3 and 7 days throughout brains of gp120-treated rats, especially in the cerebral cortex. In this area, most of the apoptotic cells exhibited a pyramidal shape and were Nissl positive, indicative of neurons. Few non-neuronal cells exhibited signs of apoptosis. The results of the present study support the notion that gp120 is neurotoxicin vivo and provide evidence that gp120 activates a caspase-dependent apoptotic pathway.     

The HIV Protein gp120 Alters Mitochondrial Dynamics in Neurons

Neurotoxicity of human immunodeficiency virus-1 (HIV) includes synaptic simplification and neuronal apoptosis. However, the mechanisms of HIV-associated neurotoxicity remain unclear, thus precluding an effective treatment of the neurological complications. The present study was undertaken to characterize novel mechanisms of HIV neurotoxicity that may explain how HIV subjects develop neuronal degeneration. Several neurodegenerative disorders are characterized by mitochondrial dysfunction; therefore, we hypothesized that HIV promotes mitochondrial damage. We first analyzed brains from HIV encephalitis (HIVE) by electron microscopy. Several sections of HIVE subjects contained enlarged and damaged mitochondria compared to brains from HIV subjects with no neurological complications. Similar pathologies were observed in mice overexpressing the HIV protein gp120, suggesting that this viral protein may be responsible for mitochondrial pathology found in HIVE. To gain more information about the cellular mechanisms of gp120 neurotoxicity, we exposed rat cortical neurons to gp120 and we determined cellular oxygen consumption rate, mitochondrial distribution, and trafficking. Our data show that gp120 evokes impairment in mitochondrial function and distribution. These data suggest that one of the mechanisms of HIV neurotoxicity includes altered mitochondrial dynamics in neurons.     

Protective effects of curcumin against human immunodeficiency virus 1 gp120 V3 loop-induced neuronal injury in rats

Curcumin improves the learning and memory deficits in rats induced by the gp120 V3 loop. The present study cultured rat hippocampal neurons with 1 nM gp120 V3 loop and 1 μM curcumin for 24 hours. The results showed that curcumin inhibited the gp120 V3 loop-induced mitochondrial membrane potential decrease, reduced the mRNA expression of the pro-apoptotic gene caspase-3, and attenuated hippocampal neuronal injury.     

Reduction of cerebral glucose utilization by the HIV envelope glycoprotein Gp-120

Gp-120 is a glycoprotein constituent of the human immunodeficiency virus (HIV) envelope. The effects of gp-120 on cerebral glucose utilization in rats were studied by the quantitative 2-deoxy-D-[1-14C] glucose method. Intracerebroventricular injection of gp-120 significantly reduced glucose utilization in the lateral habenula and the suprachiasmatic nucleus and decreased the global cerebral metabolic rate for glucose. The findings suggest that gp-120 and closely related peptides can alter neuronal function, thereby contributing to the sequelae of HIV infection.     

Plasma gelsolin protects HIV-1 gp120-induced neuronal injury via voltage-gated K+ channel Kv2.1

Plasma gelsolin (pGSN), a secreted form of gelsolin, is constitutively expressed throughout the central nervous system (CNS). The neurons, astrocytes and oligodendrocytes are the major sources of pGSN in the CNS. It has been shown that levels of pGSN in the cerebrospinal fluid (CSF) are decreased in several neurological conditions including HIV-1-associated neurocognitive disorders (HAND). Although there is no direct evidence that a decreased level of pGSN in CSF is causally related to the pathogenesis of neurological disorders, neural cells, if lacking pGSN, are more vulnerable to cell death. To understand how GSN levels relate to neuronal injury in HAND, we studied the effects of pGSN on HIV-1 gp120-activated outward K⁺ currents in primary rat cortical neuronal cultures. Incubation of rat cortical neurons with gp120 enhanced the outward K⁺ currents induced by voltage steps and resulted in neuronal apoptosis. Treatment with pGSN suppressed the gp120-induced increase of delayed rectifier current (I_K) and reduced vulnerability to gp120-induced neuronal apoptosis. Application of Guangxitoxin-1E (GxTx), a Kv2.1 specific channel inhibitor, inhibited gp120 enhancement of I_K and associated neuronal apoptosis, similar effects to pGSN. Western blot and PCR analysis revealed gp120 exposure to up-regulate Kv2.1 channel expression, which was also inhibited by treatment with pGSN. Taken together, these results indicate pGSN protects neurons by suppressing gp120 enhancement of I_K through Kv2.1 channels and reduction of pGSN in HIV-1-infected brain may contribute to HIV-1-associated neuropathy.     

Transgenic mice expressing HIV-1 envelope protein gp120 in the brain as an animal model in neuroAIDS research

HIV-1 infection causes injury to the central nervous system (CNS) and is often associated with neurocognitive disorders. One model for brain damage seen in AIDS patients is the transgenic (tg) mouse expressing a soluble envelope protein gp120 of HIV-1 LAV in the brain in astrocytes under the control of the promoter of glial fibrillary acidic protein. These GFAP-gp120tg mice manifest several key neuropathological features observed in AIDS brains, such as decreased synaptic and dendritic density, increased numbers of activated microglia, and pronounced astrocytosis. Several recent studies show that brains of GFAP-gp120tg mice and neurocognitively impaired HIV patients share also a significant number of differentially regulated genes, activation of innate immunity and other cellular signaling pathways, disturbed neurogenesis, and learning deficits. These findings support the continued relevance of the GFAP-gp120tg mouse as a useful model to investigate neurodegenerative mechanisms and develop therapeutic strategies to mitigate the consequences associated with HIV infection of the CNS, neuroAIDS, and HAND.     

Memantine prevents HIV coat protein-induced neuronal injury in vitro.

Studies with in vitro model systems suggest that at least part of the neurologic deficits of human immunodeficiency virus (HIV)-1-associated cognitive/motor complex may stem from neuronal injury mediated by the HIV-1 coat protein gp120. Concurrent activation of N-methyl-D-aspartate (NMDA) receptors is also necessary for gp120 to induce neuronal damage. We studied memantine, a drug that blocks NMDA receptor-operated ion channels, for possible protective effects from gp120-induced neuronal injury. In identified rat retinal ganglion cells in culture, we found that 2 microM memantine completely prevented the injury engendered by 20 pM gp120. These data suggest that memantine has therapeutic potential as an NMDA antagonist capable of ameliorating neuronal damage associated with gp120.     

Neuronal injury due to HIV-1 envelope protein is blocked by anti-gp120 antibodies but not by anti-CD4 antibodies

Picomolar concentrations of native or recombinant coat protein gp120, from the human immunodeficiency virus type 1 (HIV-1), injured rat retinal ganglion cell neurons in culture. This form of neurotoxicity could be completely abrogated by anti-gp120 but not by control preimmune serum, suggesting that the lethal effects of the purified preparations of the envelope protein were due to gp120 and not to a contaminant. Entry of HIV-1 is mediated by gp120 binding to a surface protein, designated "CD4," which is located, for example, on T lymphocytes. However, in the present study, specific anti-CD4 antibodies, at concentrations known to block effects mediated by high-affinity binding to CD4 on the surface of rat T cells, did not prevent neuronal injury induced by gp120. These findings suggest that injury of central neurons engendered by gp120 may be responsible, at least in part, for the neurologic manifestations observed in as many as 2/3 of the patients with acquired immunodeficiency syndrome, such as dementia, myelopathy, and visual loss, even in the absence of superinfection. In contrast with previous studies, however, this report suggests that the deleterious effects of gp120 on neurons may not be mediated via binding to the CD4 molecule.     

7-Chlorokynurenate Ameliorates Neuronal Injury Mediated by HIV Envelope Protein gp120 in Rodent Retinal Cultures

Prior studies with in vitro model systems have suggested that at least part of the neurological manifestations of AIDS may stem from neuronal injury involving the HIV-1 coat protein gp120. This form of neuronal damage is most probably mediated indirectly by a complex set of cellular interactions among macrophages, astrocytes, and neurons, resulting in a final common pathway of overstimulation of N -methyl- d -aspartate (NMDA) receptors. We studied the neuroprotective effect from gp120-induced neuronal injury of an antagonist of the glycine site of the NMDA receptor, 7-chlorokynurenate. In identified rat retinal ganglion cells in culture, we found that 50 μM 7-chlorokynurenate significantly abrogated the injury engendered by 20 pM gp120. Addition of 300 μM exogenous glycine prevented this protective effect of 50 μM 7-chlorokynurenate. These data suggest that glycine site antagonists of the NMDA receptor may have therapeutic potential for ameliorating neuronal damage associated with gp120.     

Curcumin improves synaptic plasticity impairment induced by HIV-1gp120 V3 loop

Curcumin has been shown to significantly improve spatial memory impairment induced by HIV-1 gp120 V3 in rats, but the electrophysiological mechanism remains unknown. Using extracellular microelectrode recording techniques, this study confirmed that the gp120 V3 loop could suppress long-term potentiation in the rat hippocampal CA1 region and synaptic plasticity, and that curcumin could antagonize these inhibitory effects. Using a Fura-2/AM calcium ion probe, we found that curcumin resisted the effects of the gp120 V3 loop on hippocampal synaptosomes and decreased Ca²⁺ concentration in synaptosomes. This effect of curcumin was identical to nimodipine, suggesting that curcumin improved the inhibitory effects of gp120 on synaptic plasticity, ameliorated damage caused to the central nervous system, and might be a potential neuroprotective drug.