Potent gp120-like neurotoxic activity in the cerebrospinal fluid of HIV-infected individuals is blocked by peptide T

gp120-derived amyloidogenic peptides form amyloid fibrils that increase HIV-1 infectivity

Apart from mediating viral entry, the function of the free HIV-1 envelope protein (gp120) has yet to be elucidated. Our group previously showed that EP2 derived from one β-strand in gp120 can form amyloid fibrils that increase HIV-1 infectivity. Importantly, gp120 contains ~30 β-strands. We examined whether gp120 might serve as a precursor protein for the proteolytic release of amyloidogenic fragments that form amyloid fibrils, thereby promoting viral infection. Peptide array scanning, enzyme degradation assays, and viral infection experiments in vitro confirmed that many β-stranded peptides derived from gp120 can indeed form amyloid fibrils that increase HIV-1 infectivity. These gp120-derived amyloidogenic peptides, or GAPs, which were confirmed to form amyloid fibrils, were termed gp120-derived enhancers of viral infection (GEVIs). GEVIs specifically capture HIV-1 virions and promote their attachment to target cells, thereby increasing HIV-1 infectivity. Different GAPs can cross-interact to form heterogeneous fibrils that retain the ability to increase HIV-1 infectivity. GEVIs even suppressed the antiviral activity of a panel of antiretroviral agents. Notably, endogenous GAPs and GEVIs were found in the lymphatic fluid, lymph nodes, and cerebrospinal fluid (CSF) of AIDS patients in vivo. Overall, gp120-derived amyloid fibrils might play a crucial role in the process of HIV-1 infectivity and thus represent novel targets for anti-HIV therapeutics.

Synergistic cooperation between methamphetamine and HIV-1 gsp120 through the P13K/Akt pathway induces IL-6 but not IL-8 expression in astrocytes

HIV-1 envelope protein gp120 has been extensively studied for neurotoxic effects that have been attributed to the increased expression of various proinflammatory cytokines in the CNS. Recently we have shown that methamphetamine (MA) also increases expression of proinflammatory cytokines in astrocytes. However, combined effect of gp120 and MA is not known. The present study was undertaken to determine cumulative effect and the mechanism(s)/pathways involved in the functional interaction between gp120 and MA in SVGA astrocytes. Our results clearly suggest that gp120 and MA affect IL-6 but not IL-8 in a synergistic manner and this synergy was mediated by PI3K/Akt and NF-κB pathways. Inhibition of either of these pathways could abrogate the increased expression of IL-6 due to MA or gp120 alone, as well as the increased expression of IL-6 when the astrocytes were treated with both gp120 and MA. These results were confirmed by both, using chemical inhibitors/siRNA as well as western blotting. This study therefore provides novel information regarding the interaction between MA and gp120 in terms of the expression of IL-6 and the mechanisms underlying potential synergy between MA and gp120 in astrocytes.

Accumulation of nuclear and mitochondrial DNA damage in the frontal cortex cells of patients with HIV-associated neurocognitive disorders

Oxidative stress has been suggested to play a key role in the neuropathogenesis of HIV infection. HIV proteins (gp120, Tat) and proinflammatory cytokines can trigger the production of reactive oxygen species (ROS), resulting in DNA and RNA lesions. Among all the lesions induced by ROS, one of the most abundant lesions in DNA and RNA is 8-hydroxydeoxyguanosine (8-oxoG). Here, we studied accumulated DNA oxidative damage induced by ROS in the central nervous system (CNS) in tissue from neuro-AIDS patients. The frontal cortex of autopsy tissue from HIV-1 infected patients was adopted for analysis for HIV-1 subtype, nuclear and mitochondrial DNA lesions by immunofluorescence staining, qPCR and sequencing of PCR cloning. This study provides evidence that HIV infection in the CNS leads to nuclear and mitochondrial genomic DNA damage in the brain. High level of nuclear and mtDNA 8-oxoG damage were identified in the cortex autopsy tissue of HAND patients. Increased accumulation of mtDNA mutations and depletion occurs in brain tissue in a subset of HAND cases, and is significantly different from that observed in control cases. These findings suggest that higher level of ROS in the CNS of HAND patients would contribute to the HIV induced neuro-inflammation and apoptosis of neuronal and glial cells.

Up-regulation of the neuronal nicotinic receptor α7 by HIV glycoprotein 120: potential implications for HIV-associated neurocognitive disorder

Approximately 30-50% of the >30 million HIV-infected subjects develop neurological complications ranging from mild symptoms to dementia. HIV does not infect neurons, and the molecular mechanisms behind HIV-associated neurocognitive decline are not understood. There are several hypotheses to explain the development of dementia in HIV(+) individuals, including neuroinflammation mediated by infected microglia and neuronal toxicity by HIV proteins. A key protein associated with the neurological complications of HIV, gp120, forms part of the viral envelope and can be found in the CSF of infected individuals. HIV-1-gp120 interacts with several receptors including CD4, CCR5, CXCR4, and nicotinic acetylcholine receptors (nAChRs). However, the role of nAChRs in HIV-associated neurocognitive disorder has not been investigated. We studied the effects of gp120(IIIB) on the expression and function of the nicotinic receptor α7 (α7-nAChR). Our results show that gp120, through activation of the CXCR4 chemokine receptor, induces a functional up-regulation of α7-nAChRs. Because α7-nAChRs have a high permeability to Ca(2+), we performed TUNEL staining to investigate the effects of receptor up-regulation on cell viability. Our data revealed an increase in cell death, which was blocked by the selective antagonist α-bungarotoxin. The in vitro data are supported by RT-PCR and Western blot analysis, confirming a remarkable up-regulation of the α7-nAChR in gp120-transgenic mice brains. Specifically, α7-nAChR up-regulation is observed in mouse striatum, a region severely affected in HIV(+) patients. In summary, CXCR4 activation induces up-regulation of α7-nAChR, causing cell death, suggesting that α7-nAChR is a previously unrecognized contributor to the neurotoxicity associated with HIV infection.

Gatekeeper role of 14-3-3tau protein in HIV-1 gp120-mediated apoptosis of human endothelial cells by inactivation of Bad

OBJECTIVE

HIV-1-associated dementia (HAD) is a major neurological complication often observed in the advanced stages of AIDS. We have reported that 14-3-3 proteins in cerebrospinal fluid, reflecting neuronal cell destruction, is a real-time marker of HAD progression. This study was designed to examine the role of 14-3-3 proteins in HAD.

DESIGN

An in-vitro human umbilical vein endothelial cells (HUVEC) model of gp120 protein-induced apoptosis to study the protective role of 14-3-3 in HIV-1 gp120/CXCR4-mediated cell death.

METHODS

The alpha-chemokine receptor-mediated cell death by HIV-1 envelope protein, gp120, the critical event that causes neuron loss and endothelial cell injury, was evaluated in HUVEC undergoing gp120-induced apoptosis through the CXCR4 receptor. We studied the effects of siRNA for each 14-3-3 isoform on the death of HUVEC treated with CXCR4-preferring gp120 (IIIB).

RESULTS

Gp120 increased the expression of 14-3-3tau in HUVEC. The binding of Gp120 to CXCR4 induced apoptosis of HUVEC through decreased binding of 14-3-3tau to the pro-apoptotic molecule, Bad. Treatment of the cells with dsRNA against 14-3-3tau enhanced the gp120-mediated dephosphorylation of Bad and its association with Bcl-XL in mitochondria, accelerating the gp120-induced apoptosis, whereas suppression of Bad by RNAi rescued the cells from apoptosis triggered by gp120.

CONCLUSIONS

The specific up-regulation of 14-3-3tau in HUVEC negatively regulated gp120/CXCR4-mediated cell death by protecting Bad dephosphorylation.

Regulation of neural cell survival by HIV-1 infection

Infection by the lentivirus, human immunodeficiency virus type 1 (HIV-1), results in a variety of syndromes involving both the central (CNS) and the peripheral (PNS) nervous systems. Productive HIV-1 infection of the CNS is chiefly detectable in perivascular macrophages and microglia. HIV-1 encoded transcripts and proteins have also been detected in the PNS; however, productive viral replication appears to be sparse and restricted to the macrophage cell population. Despite the absence of productive infection of neurons, HIV-1 infection has been associated with neuronal loss in distinct regions of the brain. Neuronal cell loss may occur through both necrosis and apoptosis, although neuronal apoptosis appears to be a feature of AIDS, as only rare apoptotic neurons have been demonstrated in a few pre-AIDS cases. Although there is no clear consensus as to the underlying mechanism of HIV-induced neuropathogenesis, two complementary concepts predominate. Firstly, HIV-1 encoded proteins injure neurons directly without requiring the intermediary functions of nonneuronal cells. Alternatively, neuronal apoptosis may result indirectly from the secretion of neurotoxic host molecules by resident brain macrophages or microglia in response to HIV-1 infection, stimulation by viral proteins or immune activation. Herein, we review the neurological disorders and their underlying mechanisms associated with HIV infection, focusing on HIV-associated dementia (HAD) and HIV sensory neuropathy (HIV-SN). The evidence that neuronal loss in HIV-1-infected individuals may be due to neuronal apoptosis is then discussed. This review also summarizes the current data supporting both the direct and indirect mechanisms by which neuronal death may occur during infection with HIV-1 or the closely related lentiviruses SIV and FIV. Lastly, strategies are examined for treating or preventing HAD by targeting specific neurotoxic mechanisms.

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.

Apoptosis of uninfected cells induced by HIV envelope glycoproteins

Apoptosis, or programmed cell death, is a key event in biologic homeostasis but is also involved in the pathogenesis of many human diseases including human immunodeficiency virus (HIV) infection. Although multiple mechanisms contribute to the gradual T cell decline that occurs in HIV-infected patients, programmed cell death of uninfected bystander T lymphocytes, including CD4+ and CD8+ T cells, is an important event leading to immunodeficiency. The HIV envelope glycoproteins (Env) play a crucial role in transducing this apoptotic signal after binding to its receptors, the CD4 molecule and a coreceptor, essentially CCR5 and CXCR4. Depending on Env presentation, the receptor involved and the complexity of target cell contact, apoptosis induction is related to death receptor and/or mitochondria-dependent pathways. This review summarizes current knowledge of Env-mediated cell death leading to T cell depletion and clinical complications and covers the sometimes conflicting studies that address the possible mechanisms of T cell death.

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- and FIV-derived gp120 alter spatial memory, LTP, and sleep in rats

Human immunodeficiency virus (HIV)-associated dementia (HAD) has been detected in 20-30% of patients suffering AIDS. The envelope glycoprotein 120 (gp120) derived from HIV seems to play a critical role in the pathophysiology of this dementia. Likewise, the feline immunodeficiency virus (FIV)-derived gp120 causes neurological and electrophysiological abnormalitites in cats. We have studied the effects of gp120 derived from HIV or FIV on learning and memory processing, hippocampal long-term potentiation (LTP), hippocampal neuronal cAMP production, the sleep-waking cycle, and locomotor activity and equilibrium in rats. Results showed that while both HIV- and FIV-gp120 impaired the rat's performance in the Barnes maze task, only HIVgp120 impaired the induction and maintenance of LTP. However, both glycoproteins induced a significant decrease in the posttetanic potentiation. HIVgp120 also caused a significant reduction in cAMP production in the hippocampus. Regarding the sleep-waking cycle, HIV- and FIV-gp120 increased the waking state and slow-wave sleep 1 (SWS1), while decreasing both SWS2 and REM sleep. Locomotor activity and equilibrium were significantly altered by these glycoproteins. These results suggest that HIVgp120 causes neurophysiological abnormalities and therefore may facilitate HAD development in AIDS patients.

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.

Peptide T-araC conjugates: solid-phase synthesis and biological activity of N4-(acylpeptidyl)-araC

Due to the capability of peptidyl derivatives of araC to behave as prodrugs of this antimetabolite, and because of the well known biological properties of peptide T and its analogues (in particular that of targeting CD4+ cells), new peptide T-araC conjugates were prepared and tested in vitro for antiproliferative activity. The aim was that of specifically delivering the antitumor drug to CD4+ cells. N4-(Acylpeptidyl)-derivatives of araC were synthesized by a new general approach involving solid-phase synthesis, which allows mild conditions, avoids the usually required protection of the glycoside portion of nucleosides and affords high yields of the final products. After the demonstration that peptide T-araC conjugates were able to activate chemotaxis by binding CD4 receptor on monocyte membranes, the antiproliferative activity was evaluated against a panel of leukemia lymphoma and carcinoma cell lines derived from human tumors, three CD4+ cell lines included. Title compounds resulted effective as antiproliferative agents at concentrations 4- to 10-fold higher than those of araC alone, did not preferentially inhibit CD4+ cells and proved stable not only in cell culture medium containing 20% FCS, but also in human plasma. All this suggests their potential utility in vivo.

Methylation of cortical brain proteins from patients with HIV infection

OBJECTIVES

Experimental models of vitamin B12 deficient-neuropathy are characterized by central nervous system protein hypomethylation. The encephalitis/vacuolar myelopathy complicating HIV infection and subacute combined degeneration of the cord due to vitamin B12 deficiency share similar biochemical and pathological abnormalities. Altered central nervous system methylation may be important in the pathogenesis of HIV encephalitis. To test this hypothesis we compared brain protein methylation of HIV-positive, and control, subjects.

MATERIALS AND METHODS

Carboxymethyltransferase activity was assayed in postmortem cortical brain samples obtained from 16 control patients (9 males); mean age (59+/-5.1 years, range 21-87 years), 9 HIV-positive patients (7 males, 6 IVDA, 3 homosexual, 4 with HIV encephalitis, mean age 37, range 23-45), and 3 patients with Alzheimer's disease (mean age 78 years).

RESULTS

The amount of radiolabelled SAM (S-adenosylmethionine) incorporated into carboxymethyl, and N-methylation sites within brain proteins from cortical white matter in vitro was significantly lower (P<0.05) in the HIV+ group vs controls. Carboxymethyltransferase activity was similar in the HIV-infected brains irrespective of the presence or absence of HIV encephalitis. Mean cortical methyl group incorporation was also lower in the Alzheimer's disease group compared to controls.

CONCLUSION

The observation of reduced in vitro methylation of brain proteins from patients with HIV infection and Alzheimer's disease suggests that fewer unmethylated sites exist due to relative protein hypermethylation in vivo. The absence of hypomethylation in the brains of patients with HIV encephalitis suggests that hypomethylation is not necessary for the development of HIV encephalitis.

HIV envelope protein gp120 induces neuropeptide Y receptor-mediated proliferation of vascular smooth muscle cells: relevance to AIDS cardiovascular pathogenesis

Hyperplasia of vascular smooth muscle cells (VSMCs) occurs during HIV infection, part of a spectrum of HIV-mediated cardiovascular and microvascular pathologies. These changes are not due to direct viral infection but may involve the receptor-mediated action of viral proteins, such as the envelope protein gp120. We sought to identify gp120 receptors which might mediate the vascular smooth muscle cell hyperplasia present in HIV infection. A homology between neuropeptide Y (NPY) and the previously identified receptor-active V2-region of gp120 defined by an octapeptide sequence (Peptide T) related to VIP was noted. Since NPY is mitogenic for VSMCs we therefore determined whether gp120 shares this activity. Rat aortic VSMCs were treated for 24 h with human (h)NPY and gp120 in the presence of 0.5% serum to measure [3H]thymidine incorporation, an index of cell proliferation. NPY increased [3H]thymidine incorporation by 80% after a 24-h treatment in a bimodal fashion, with peak effects at 10(-10) M and 10(-8) M. Gp120 was an even more potent mitogen for VSMCs with peak activity occurring at 10(-12) M. Peptide T was equipotent with gp120, and slightly less efficacious, suggesting that this domain may mediate gp120 effects on VSMCs. When combined, gp120 and NPY acted to antagonize one another, lowering DNA synthesis to basal levels. The profile of pharmacologic inhibition supports a role for NPY receptors since antagonists of Y1 and Y2 subtypes substantially or completely inhibited gp120-mediated VSMC proliferation. This is the first demonstration of the proliferative effects of HIV viral protein gp120 on VSMCs. The effect appears to be mediated via gp120 sequences related to VIP, peptide T, and NPY. These ligands may be competitive inhibitors of binding or gp120 processing. Novel treatments may emerge based upon VIP and NPY receptor antagonists if further work substantiates a role for gp120 in the vascular abnormalities of AIDS.

The effects of human immunodeficiency virus in the central nervous system

More than a decade after the first description of HIV DNA in the nervous system the pathophysiology of HIVD remains largely enigmatic, with data supporting a number of potential mechanisms for the development of neuronal dysfunction. Nevertheless, a few key findings have considerable support in the literature devoted to this subject: 1. HIV dementia is caused by HIV itself; no other pathogen has been consistently found in the brains of patients with HIVD. 2. In comparison with other viral encephalopathies, there appears to be a significant discordance between the amount of virus being produced in the brains of patients with HIVD and the degree of neurological deterioration. 3. The key cell types responsible for viral production within the CNS are the resident macrophages or microglial cells. 4. Other elements within the CNS, particularly astrocytes, are probably infected with HIV as well, but all of these infections are highly restricted in terms of production of virus or viral structural proteins. 5. At least one component of the pathogenesis of HIVD may be the generation of neurotoxins by infected microglia, although the type of neurotoxin, and the specific compound most likely to be involved, are quite controversial. Advances with combination antiviral therapy have successfully reduced plasma viral load in a high proportion of individuals, leading to the speculation (previously almost heretical) that it may be possible to eradicate HIV completely from the systemic immune system. If that were the case, potential "sanctuary" sites such as the immunologically protected CNS might remain as important reservoirs for reseeding of lymphoid tissues. Microglia may be particularly suited for this purpose because they are long lived, can produce HIV for several weeks (at least in culture), and they are apparently relatively immune to virus-induced cytopathology such as syncytium formation. One can speculate about several scenarios resulting from the continued presence of replication-competent HIV within brain. In the worst case, a smoldering infection of the nervous system could lead to neurological deterioration without reinfection of systemic immune cells. The epidemiological data indicating that HIVD is a disease primarily associated with immunodeficiency suggest that the systemic immune system plays a role in maintaining virus residing within the CNS under control. Thus it is quite possible that this scenario would not occur for many years after the systemic infection is controlled. Alternatively, virus could be transported from the CNS by circulating lymphocytes and monocytes and reinfect systemic organs. This would necessitate restarting therapy for those individuals who were previously thought to be cured, but presumably virus within the CNS would not have developed resistance to antivirals. In either case, the techniques currently available do not permit an accurate assessment of CNS HIV load in living people, and this question will remain unanswered until antivirals are discontinued in a few individuals with persistently negative tests for systemic virus. In addition to this most critical question, the relationship between viral levels and HIVD is largely unexplored, as is the possibility that some strains are particularly virulent or neuroinvasive. Furthermore, the potential contribution of host genotype in the development of dementia is unknown. In view of the strong influence of major chemokine receptor (CCR5) truncations on HIV replication, it is entirely possible that more discrete genetic polymorphisms have a subtle effect on either brain invasion or virulence.

Effects of [D-Ala1] peptide T-NH2 and HIV envelope glycoprotein gp120 on cyclic AMP dependent protein kinases in normal and psoriatic human fibroblasts

In addition to acquired immunodeficiency syndrome (AIDS), persons infected with human immunodeficiency virus often develop cutaneous manifestations, including severe psoriasis. In previous studies, we have established that psoriatic fibroblasts and erythrocytes obtained from psoriatic patients exhibit decreased levels of cyclic adenosine monophosphate (cAMP) dependent protein kinase (PKA) activity and of 8-azido-[32P]cAMP binding to the RI and RII regulatory subunits of PKA. Because treatment of patients with peptide T (an octapeptide sequence found in the human immunodeficiency virus envelope glycoprotein gp120) has been observed to result in an improvement in the psoriatic condition, studies were initiated to determine if peptide T and gp120 protein treatment of normal and psoriatic human fibroblasts resulted in any changes in PKA. Exposure of psoriatic fibroblasts to peptide T resulted in a time (4 h to 6 d) and dose [10(-14)-10(-8) M] dependent increase in the levels of 8-azido-[32P]cAMP binding to the RI and RII regulatory subunits of PKA, along with a corresponding increase in PKA activity. Peptide T exhibited a biphasic dose dependent response, with maximal effects on PKA noted at 10(-12)M peptide T. Treatment of normal human fibroblasts with peptide T did not result in any change in PKA levels. Conversely, treatment of normal human fibroblasts for 18 h with gp120 protein [10(-13) M] resulted in a significant decrease in the levels of 8-azido-[32P]cAMP binding to RI and RII and in PKA activity. The presence of peptide T blocked this effect of the gp120 protein. These results indicate that peptide T and gp120 protein may inversely alter the intracellular levels of 8-azido-[32P]cAMP binding to RI and RII, and of PKA activity in susceptible cells. These observed changes in the cyclic AMP-PKA signaling pathway, a biochemical marker for psoriasis, may offer some mechanistic insight into the noted beneficial effects of peptide T treatment, including an improvement in psoriatic lesions.

Hypotensive effects of peptide T in conscious rats

1. The present study investigated the effects of peptide T on mean arterial blood pressure (MAP) in conscious normotensive Sprague-Dawley (SD) rats, spontaneously hypertensive rats (SHR) and two-kidney one-clip (2K1C) hypertensive rats. 2. Peptide T was infused via the left jugular vein at a rate of 1 mg/kg per h in SD, SHR and 2K1C rats and then at doses of 0.1, 0.25, 0.5, 1 and 5 mg/kg per h in SHR, with 0.9% saline as a sham control in SHR and 2K1C. Mean arterial pressure was measured directly before, during and after infusion. 3. Peptide T (1 mg/kg per h) decreased blood pressure in both SHR (P < 0.01) and 2K1C (P < 0.05). In normotensive SD rats the fall in MAP approached statistical significance (P = 0.06). The effect of peptide T was not significantly different in normotensive compared with hypertensive rats. Saline infusion had no effect. The blood pressure lowering effect of peptide T appeared to be dose-dependent in SHR.

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

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

HIV-1 gp120 Effects on Signal Transduction Processes and Cytokines: Increased src-Family Protein Tyrosine Kinase Activity

Varying degrees of neurological dysfunction are observed in AIDS patients who develop AIDS dementia complex (ADC). Data from a large number of in vivo and in vitro rodent studies have suggested a role for the HIV envelope glycoprotein gp 120 in this process. These studies were initiated to clarify possible effects of recombinant gp120 on signal transduction systems and the synthesis of specific ADC-related cytokines in human neuroblastoma cells. Out results indicate that gp120 on signal transduction systems and the synthesis of specific ADC-related cytokines in human neuroblastoma cells. Our results indicate that gp120 did not induce the synthesis of cAMP, IPs or NO, nor did it alter agonist-induced synthesis of these molecules. In addition, it did not induce the synthesis of IL-6 and TNF&#945;. However, it did activate a src-family protein tyrosine kinase which phosphorylates several substrates, including prominent proteins in the 115 and 60 kDa range. This gp120-induced tyrosine phosphorylation may contribute to neurological dysfunction since protein tyrosine kinases are known to be involved in processes important for pre- and post-synaptic neuronal function.

AIDS Dementia and HIV-1-Induced Neurotoxicity: Possible Pathogenic Associations and Mechanisms

AIDS Dementia Complex (ADC) is a syndrome of cognitive, behavioral, and motor deficits resulting from HIV-1 infection within the brain. ADC is characterized by variable degrees of neuronal cell death and gliosis that likely result, at least, in part from release of metabolic products, cytokines, and viral proteins from infected macrophages, although a unifying explanation for the neurological dysfunction has yet to be established. Major unanswered questions include: (i) do neurologic symptoms result from neuronal cell death and/or dysfunction in surviving neurons?; (ii) are viral genomic sequences determinants of neurotoxicity?; (iii) is HIV infection of neurons and astrocytes relevant to pathogenesis?, and (iv) what circulating factors within the brain affect neuronal cell survival and function? This review addresses the association between HIV-1 replication within the brain, production of potential neurotoxins and possible mechanisms of induction of neurotoxicity and neuronal dysfunction contributing to the pathogenesis of ADC. Copyright 1996 S. Karger AG, Basel

Passage of peptides across the blood-brain barrier: pathophysiological perspectives

Blood-borne peptides are capable of affecting the central nervous system (CNS) despite being separated from the CNS by the blood-brain barrier (BBB), a monolayer comprised of brain endothelial and ependymal cells. Blood-borne peptides can directly affect the CNS after they cross the BBB by nonsaturable and saturable transport mechanisms. The ability of peptides to cross the BBB to a meaningful degree suggests that the BBB may act as a modulatory pathway in the exchange of informational molecules between the brain and the peripheral circulation. The permeability of the BBB to peptides is a regulatory process affected by developmental, physiological, and pathological events. This regulation sets the stage for the relation between peptides and the BBB to be involved in pathophysiological events. For example, some of the classic actions of melanocortins on the CNS are explained by their abilities to cross the BBB, whereas aspects of feeding and alcohol-related behaviors are associated with the passage of other specific peptides across the BBB. The BBB should no longer be considered a static barrier but should be recognized as a regulatory interface controlling the exchange of informational molecules, such as peptides, between the blood and CNS.

Acquired immune deficiency syndrome: the glucocorticoid solution

Documented evidence supports the "cortisol connection' theory of acquired immune deficiency syndrome, linking glucocorticoid metabolism with immune function, and human immunodeficiency virus with them both. The peptide T subregion of gp 120 of human immunodeficiency virus apparently utilizes cellular melanocyte stimulating hormone receptors to competitively inhibit the blocking of interleukin-1 by melanocyte-stimulating hormone. Interleukin-1 stimulates CD8+ T-lymphocyte proliferation, as well as causing the release of corticotropin-releasing hormone, thereby stimulating the release of adrenocorticotrophic hormone and cortisol. Gp 120 also induces upregulation of adrenocorticotrophic hormone-related messenger ribonucleic acid. This apparently separate glucocorticoid metabolic route utilized by human immunodeficiency virus is the basis of the cortisol excess seen in human immunodeficiency virus infection. In vitro glucocorticoid-resistant lymphoid cells are resistant to human immunodeficiency virus infection as well. Viral resistance is also observed in patients who demonstrate glucocorticoid resistance. Glucocorticoid-responsive elements are contained in the human immunodeficiency virus (proviral and viral) genome that appear to regulate human immunodeficiency virus replication. Similarly, lymphoid-cell development and regulation depend on glucocorticoids. One may take advantage of this view of human immunodeficiency virus pathogenesis to create new methods of treatment.

HIV-1 gp120-induced neurotoxicity to midbrain dopamine cultures

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

Investigation into the intestinal metabolism of [D-Ala1] peptide T amide: implication for oral drug delivery

The anti-AIDS drug, [D-Ala1] Peptide T amide (D-ASTTTNYT.NH2) is an octapeptide which competitively inhibits the attachment of HIV to the receptor CD4 molecule on the T-lymphocyte. The objective of the study is to investigate the degradative process of this peptide and its effective enzyme inhibitors. The metabolites of [D-Ala1] Peptide T amide in rabbit brush-border membrane vesicles at pH 6.5 are ASTT, ASTTTN, YT and Y. The sequential time-course study of each metabolite reveals that enkephalinase (EC 3.4.24.11) plays an important role in the hydrolysis of [D-Ala1] Peptide T amide to ASTT. With the addition of an enkephalinase inhibitor, thiorphan, 85% of degradation was inhibited. Aminopeptidase is also involved in its degradative process and 25% of inhibition was observed by amastatin, an aminopeptidase inhibitor. The results show that no significant difference was observed between the in situ and chronical loop perfusion studies and enzyme activities are somewhat inhibited under acidic conditions in both methods. Approx. 90% of the parent peptide remained when rats were perfused with pH 4.0 peptide solution at a flow rate of 0.123 ml/min, while only 60% was recovered when pH 6.5 peptide solution was applied. The addition of amastatin made a quadrupled increase in the amount of parent peptide recovered. A 117-fold increment was observed when thiorphan was added. The dimensionless wall permeability of this peptide was 1.19 +/- 0.16 when pH 4.0 peptide solution was used during chronical loop perfusion study. Therefore, this study suggests that [D-Ala1] Peptide T amide could be absorbed via small intestine where enzymatic degradation s a rate-limiting step for the absorption of this peptide.

Histopathological and immunohistochemical changes in psoriatic skin during peptide T treatment

Ten patients with plaque-type psoriasis were treated with 2 mg peptide T i.v. for 28 days. Six patients responded with a substantial clinical improvement. Sequential biopsies from skin lesions were taken before, during and after treatment. The histological score (defining the activity of the psoriasis), the epidermal thickness and the number of infiltrating dermal lymphocytes were all reduced in the six patients who responded to the treatment. An increase in the number of CD1+ dendritic cells was detected immunohistochemically in the epidermis of the responders. The nonresponders did not display any pronounced changes.

AIDS-related dementia and calcium homeostasis

Approximately a third of adults and half of children with acquired immunodeficiency syndrome (AIDS) eventually suffer from neurological manifestations, including dysfunction of cognition, movement, and sensation. Among the various pathologies reported in the brain of patients with AIDS is neuronal injury and loss. A paradox arises, however, because neurons themselves are for all intents and purposes not infected by human immunodeficiency virus type 1 (HIV-1). This paper reviews evidence suggesting that at least part of the neuronal injury observed in the brain of AIDS patients is related to excessive influx of Ca2+. There is growing support for the existence of HIV- or immune-related toxins that lead indirectly to the injury or death of neurons via a potentially complex web of interactions between macrophages (or microglia), astrocytes, and neurons. Human immunodeficiency virus-infected monocytoid cells (macrophages, microglia, or monocytes), especially after interacting with astrocytes, secrete substances that potentially contribute to neurotoxicity. Not all of these substances are yet known, but they may include eicosanoids, that is, arachidonic acid and its metabolites, as well as platelet-activating factor. Macrophages activated by HIV-1 envelope protein gp120 also appear to release arachidonic acid and its metabolites. These factors can lead to increased glutamate release or decreased glutamate reuptake. In addition, gamma interferon (IFN-gamma) stimulation of macrophages induce release of the glutamate-like agonist quinolinate. Human immunodeficiency virus-infected or gp120-stimulated macrophages also produce cytokines, including tumor necrosis factor-alpha and interleukin-1 beta, which contribute to astrogliosis. A final common pathway for neuronal susceptibility appears to be operative, similar to that observed in stroke, trauma, epilepsy, neuropathic pain, and several neurodegenerative diseases, possibly including Huntington's disease, Parkinson's disease, and amyotrophic lateral sclerosis. This mechanism involves the activation of voltage-dependent Ca2+ channels and N-methyl-D-aspartate (NMDA) receptor-operated channels, and therefore offers hope for future pharmacological intervention. This review focuses on clinically tolerated calcium channel antagonists and NMDA antagonists with the potential for trials in humans with AIDS dementia in the near future.

HIV-related neuronal injury. Potential therapeutic intervention with calcium channel antagonists and NMDA antagonists

Perhaps as many as 25-50% of adult patients and children with acquired immunodeficiency syndrome (AIDS) eventually suffer from neurological manifestations, including dysfunction of cognition, movement, and sensation. How can human immunodeficiency virus type 1 (HIV-1) result in neuronal damage if neurons themselves are for all intents and purposes not infected by the virus? This article reviews a series of experiments leading to a hypothesis that accounts at least in part for the neurotoxicity observed in the brains of AIDS patients. There is growing support for the existence of HIV- or immune-related toxins that lead indirectly to the injury or demise of neurons via a potentially complex web of interactions among macrophages (or microglia), astrocytes, and neurons. HIV-infected monocytoid cells (macrophages, microglia, or monocytes), after interacting with astrocytes, secrete eicosanoids, i.e., arachidonic acid and its metabolites, including platelet-activating factor. Macrophages activated by HIV-1 envelope protein gp120 also appear to release arachidonic acid and its metabolites. In addition, interferon-gamma (IFN-gamma) stimulation of macrophages induces release of the glutamate-like agonist, quinolinate. Furthermore, HIV-infected macrophage production of cytokines, including TNF-alpha and IL1-beta, contributes to astrogliosis. A final common pathway for neuronal susceptibility appears to be operative, similar to that observed in stroke, trauma, epilepsy, neuropathic pain, and several neurodegenerative diseases, possibly including Huntington's disease, Parkinson's disease, and amyotrophic lateral sclerosis. This mechanism involves the activation of voltage-dependent Ca2+ channels and N-methyl-D-aspartate (NMDA) receptor-operated channels, and, therefore, offers hope for future pharmacological intervention. This article focuses on clinically tolerated calcium channel antagonists and NMDA antagonists with the potential for trials in humans with AIDS dementia in the near future.

gp120 as an etiologic agent for NeuroAIDS: neurotoxicity and model systems

The search for an agent that can mediate the symptoms of NeuroAIDS has been directed at gp120, the major envelope protein from HIV. The toxicity associated with gp120 was examined as a model and predictor of the neuropathological and neuropsychiatric manifestations of AIDS. Studies of the neurotoxic effects of purified gp120 on neurons from the rodent CNS cell cultures indicated the following: potent and selective killing of subpopulations of hippocampal neurons; varying potency of gp120s obtained from various HIV isolates; complete and potent protection from gp120 killing action after treatment with peptides related to vasoactive intestinal peptide; and obligatory presence of glia for gp120-related toxicity. Investigations of gp120 treatment of rodents revealed: cortical neurodystrophy with reduced arborizations and swollen processes; delays in developmental behaviors involving motor skills; peptide T prevention or attenuation of the morphological and behavioral deficits/delays produced by administration of gp120; and impairment of learning in the Morris swim maze. In addition, studies of subcutaneously administered, radiolabeled gp120 in neonatal animals demonstrated the presence of toxic fragments of gp120 in the developing brain. With the use of model test systems of non-human derived cell cultures and neonatal rats, we have captured and predicted a number of the morphological and behavioral deficits associated with AIDS. These multi-disciplinary studies of the actions of gp120 and associated fragments in rodents and rodent cells predict that the loss of cognitive and neurological function in patients with AIDS are attributed in part to interference of critical brain functions by the envelope protein, gp120.

Complement dependent cytotoxicity of sensory ganglion neurons mediated by the gp120 glycoprotein of HIV-1

Patients infected with HIV-1 frequently have a sensory neuropathy, but the cause is unknown. We found that the gp120 glycoprotein of HIV-1 bound to the surface of cultured rat dorsal root ganglia (DRG) neurons, and activated the complement cascade to lyse the neuronal cells. Cytotoxicity was measured by a 51Cr-release assay, and deposits of the C5b-9 complement complex were detected on the affected cells. As controls, gp120 or complement alone, or rgp120 plus deactivated complement, did not damage the neuronal cells, and fibroblasts were unaffected. The gp120 glycoprotein can thereby damage DRG neurons by complement dependent mechanisms. This interaction may contribute to the development of the sensory neuropathy in AIDS.