Methamphetamine potentiates HIV-1 Tat protein-mediated activation of redox-sensitive pathways in discrete regions of the brain

Molecular mechanism(s) involved in the synergistic induction of CXCL10 by human immunodeficiency virus type 1 Tat and interferon-gamma in macrophages

Synergistic interactions between viral proteins and soluble host factors released from infected mononuclear phagocytes play a critical role in the pathogenesis of human immunodeficiency virus (HIV)-associated dementia (HAD). The chemokine CXCL10 has been found to be closely associated with the progression of HIV-1-related central nervous system (CNS) disease and its related neuropsychiatric impairment. In this report the authors demonstrate that the HIV-1 protein Tat can interact with the proinflammatory cytokine interferon (IFN)-gamma to dramatically induce the expression of CXCL10 in macrophages. Synergistic induction of CXCL10 by both Tat and IFN-gamma was susceptible to inhibition by the MEK1/2 inhibitor U0126 and the p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580. In addition, JAK/STAT pathway plays a major role in Tat/gamma-mediated CXCL10 induction in macrophages because pretreatment of stimulated macrophages with JAK inhibitor completely abrogated the synergistic induction of the chemokine. Functionality of the synergistically induced CXCL10 was further demonstrated by its chemotactic activity for peripheral blood lymphocytes. Taken together, these findings demonstrate that the cooperative interaction of Tat and IFN-gamma results in enhanced chemokine expression, which in turn can amplify the inflammatory responses within the CNS of HAD patients by recruiting more lymphocytes in the brain.

Characterizing intercellular signaling peptides in drug addiction

Intercellular signaling peptides (SPs) coordinate the activity of cells and influence organism behavior. SPs, a chemically and structurally diverse group of compounds responsible for transferring information between neurons, are broadly involved in neural plasticity, learning and memory, as well as in drug addiction phenomena. Historically, SP discovery and characterization has tracked advances in measurement capabilities. Today, a suite of analytical technologies is available to investigate individual SPs, as well as entire intercellular signaling complements, in samples ranging from individual cells to entire organisms. Immunochemistry and in situ hybridization are commonly used for following preselected SPs. Discovery-type investigations targeting the transcriptome and proteome are accomplished using high-throughput characterization technologies such as microarrays and mass spectrometry. By integrating directed approaches with discovery approaches, multiplatform studies fill critical gaps in our knowledge of drug-induced alterations in intercellular signaling. Throughout the past 35 years, the National Institute on Drug Abuse has made significant resources available to scientists that study the mechanisms of drug addiction. The roles of SPs in the addiction process are highlighted, as are the analytical approaches used to detect and characterize them.

Neurotoxic profiles of HIV, psychostimulant drugs of abuse, and their concerted effect on the brain: current status of dopamine system vulnerability in NeuroAIDS

There are roughly 30-40 million HIV-infected individuals in the world as of December 2007, and drug abuse directly contributes to one-third of all HIV infections in the United States. Antiretroviral therapy has increased the lifespan of HIV-seropositives, but CNS function often remains diminished, effectively decreasing quality of life. A modest proportion may develop HIV-associated dementia, the severity and progression of which is increased with drug abuse. HIV and drugs of abuse in the CNS target subcortical brain structures and DA systems in particular. This toxicity is mediated by a number of neurotoxic mechanisms, including but not limited to, aberrant immune response and oxidative stress. Therefore, novel therapeutic strategies must be developed that can address a wide variety of disparate neurotoxic mechanisms and apoptotic cascades. This paper reviews the research pertaining to the where, what, and how of HIV and cocaine/methamphetamine toxicity in the CNS. Specifically, where these toxins most affect the brain, what aspects of the virus are neurotoxic, and how these toxins mediate neurotoxicity.

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

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

Methamphetamine alters blood brain barrier permeability via the modulation of tight junction expression: Implication for HIV-1 neuropathogenesis in the context of drug abuse

The pathogenesis of human immunodeficiency virus (HIV) associated encephalopathy is attributed to infiltration of the central nervous system (CNS) by HIV-1 infected mononuclear cells that transmigrate across the blood brain barrier (BBB). The endothelial tight junctions (TJ) of the blood brain barrier (BBB) play a critical role in controlling cellular traffic into the CNS. Neuropathogenesis of HIV-1 is exacerbated by drugs of abuse such as methamphetamine (Meth) which are capable of dysregulating BBB function. HIV-1 viral proteins like gp120 are both neurotoxic and cytotoxic and have been implicated in the development of HIV-1 dementia (HAD). We hypothesize that gp120 in synergy with Meth can alter BBB permeability via the modulation of tight junction expression. We investigated the effect of Meth and/or gp120 on the basal expression of TJ proteins ZO-1, JAM-2, Occludin, Claudin-3 and Claudin-5, using in vitro cultures of the primary brain microvascular endothelial cells (BMVEC). Further, the functional effects of TJ modulation were assessed using an in vitro BBB model, that allowed measurement of BBB permeability using TEER measurements and transendothelial migration of immunocompetent cells. Our results show that both Meth and gp120 individually and in combination, modulated TJ expression, and these effects involved Rho-A activation. Further, both Meth and gp120 alone and in combination significantly decreased transendothelial resistance across the in vitro BBB and the enhanced transendothelial migration of immunocompetent cells across the BBB. An understanding of the mechanisms of BBB breakdown that lead to neurotoxicity is crucial to the development of therapeutic modalities for Meth abusing HAD patients.

Neurobiology of HIV

The importance of HIV cognitive impairment, including HIV associated dementia (HAD) and minor cognitive/motor disorder, has continued in the era of highly active antiretroviral therapy (HAART). Despite the relative efficacy of HAART in controlling HIV disease, there is no treatment which specifically targets the cause of HAD nor promotes neuronal protection from the effects of the virus. Much work has been done to elucidate the complex signalling pathways, effects of virus and viral proteins, and dysregulation of endogenous targets which lead to HIV associated neurotoxicity, but the concise mechanism remains elusive. It is widely accepted that the majority of viral replication in the brain occurs in monocyte derived macrophages (MDM) and microglia, and immune activation of these cells, along with astrocytic cells, may be the most important cause of neurotoxicity in the central nervous system (CNS). Additional complications arise when co-factors such as drug use, age related neuropathology, and other viruses are present. Further exploration of the molecular mechanisms leading to HIV neurotoxicity and neurodegeneration may reveal targets for prophylactic neuroprotective or other CNS-specific drugs. Given the variable success of the current HAART drugs against virus in the CNS, such therapies would greatly benefit the HIV infected population as they live longer and more productive lives.

Anti-apoptotic therapy with a Tat fusion protein protects against excitotoxic insults in vitro and in vivo

A number of gene therapy approaches have been developed for protecting neurons from necrotic neurological insults. Such therapies are limited by the need for transcription and translation of the protective protein, delaying therapeutic impact. As an alternative, we explore the neuroprotective potential of protein therapy, using a fusion protein comprised of the death-suppressing BH4 domain of the Bcl-xL protein and the protein transduction domain of the human immunodeficiency virus Tat protein. This fusion protein decreased neurotoxicity caused by the excitotoxins glutamate and kainic acid in primary hippocampal cultures, and decreased hippocampal damage in vivo in an excitotoxic seizure model.

Effects of human immunodeficiency virus and methamphetamine on cerebral metabolites measured with magnetic resonance spectroscopy

Human immunodeficiency virus (HIV) and methamphetamine (METH) use disorders are associated with cerebral dysfunction. To determine whether these effects were evident on in vivo neuroimaging, quantitative, single voxel magnetic resonance (MR) spectroscopy was used to assess frontal white matter, frontal gray matter, and basal ganglia in 40 HIV+/METH+, 66 HIV+/METH-, 48 HIV-/METH+, and 51 HIV-/METH- participants. HIV was associated with lower N-acetylaspartate (NAA) in frontal white and frontal gray matter but METH was not associated with cerebral metabolite differences in any region. Among HIV+ individuals, lower CD4 counts and higher plasma HIV viral loads were associated with lower NAA in frontal gray matter and basal ganglia. The relationship between detectable plasma HIV viral load and NAA in frontal white matter was significantly stronger in the HIV+/METH+ group, compared to HIV+/METH-. Higher detectable plasma HIV viral load was significantly associated with higher myo-inositol (MI) in frontal white and gray matter for HIV+/METH+, but not HIV+/METH-. For the HIV-/METH+ group, lifetime duration of METH use was associated with higher choline levels in frontal gray matter and higher MI levels in basal ganglia. Our findings are consistent with significant disruption of neuronal integrity in the frontal lobes of HIV-infected individuals. Although METH was not associated with cerebral metabolite levels, other findings suggested that METH use did affect the brain. For example, the relationship between detectable plasma HIV viral load and NAA levels was limited to HIV+/METH+ individuals. This evidence indicates when HIV is poorly suppressed, METH may modify the effects of the virus on neuronal integrity.

Neurobiology of HIV, psychiatric and substance abuse comorbidity research: workshop report

Viral infections can cause persistent and progressive changes in emotional and cognitive functions. The viral-induced imbalances in neuronal network functioning may precipitate or accentuate psychiatric conditions in vulnerable individuals, in part, as a function of the host response to proinflammatory cytokines resulting from infection or brain injury. Research indicates that the mediators of psychiatric illnesses and HIV-neuropathogenesis utilize similar brain structures, neurocircuitry and receptor systems. The genetic, cellular and molecular mechanisms contributing to HIV neuropathogenesis and its late stage clinical correlate, HIV-associated-dementia (HAD), are active areas of neuroAIDS research. The study of HIV in the context of psychiatric comorbidities and comorbid pathogenesis is in a fledgling stage despite epidemiological studies suggesting that >60% of HIV infected individuals will suffer from at least one major psychiatric disorder during the course of infection. Depression is the primary comorbid disorder but anxiety and substance abuse disorders are also considerable in certain HIV(+) populations. Certain substances of abuse and the biological mediators of psychiatric illnesses reportedly interact in the brain and presumptively worsen HIV-related neuropathogenesis and survival measures. A panel of experts discussed approaches for studying the neuroscience of HIV and psychiatric comorbidity at a basic, mechanistic level since they co-exist in high proportion in the human population. Recommended approaches ranged from improving human consent forms and maximizing the value of repository resources to novel research designs and identifying human and animal endophenotypes.

Cell signaling (mechanism and reproductive toxicity): redox chains, radicals, electrons, relays, conduit, electrochemistry, and other medical implications

This article deals with a novel, simple, integrated approach to cell signaling involving basic biochemical principles, and their relationship to reproductive toxicity. Initially, an overview of the biological aspects is presented. According to the hypothetical approach, cell signaling entails interaction of redox chains, involving initiation, propagation, and termination. The messengers are mainly radicals and electrons that are generated during electron transfer (ET) and hydrogen atom abstraction reactions. Termination and initiation processes in the chain occur at relay sites occupied by redox functionalities, including quinones, metal complexes, and imines, as well as redox amino acids. Conduits for the messengers, comprising species with nonbonding electrons, are omnipresent. Details are provided for the various electron transfer processes. In relation to the varying rates of cell communication, rationale is based on electrons and size of radicals. Another fit is similarly seen in inspection of endogenous precursors of reactive oxygen species (ROS); namely, proteins bearing redox moieties, lipid oxidation products, and carbohydrate radicals. A hypothesis is advanced in which electromagnetic fields associated with mobile radicals and electrons play a role. Although radicals have previously been investigated as messengers, the area occupies a minor part of the research, and it has not attracted broad consensus as an important component. For the first time, an integrated framework is presented composed of radicals, electrons, relays, conduits, and electrical fields. The approach is in keeping with the vast majority of experimental observations. Cell signaling also plays an important role in reproductive toxicity. The main classes that cause birth defects, including ROS, radiation, metal compounds, medicinals, abused drugs, and miscellaneous substances, are known to participate in the signaling process. A unifying basis exists, in that both signaling and reproductive toxicity are characterized by the electron transfer-reactive oxygen species-oxidative stress (ET-ROS-OS) scheme. This article also incorporates representative examples of the extensive investigations dealing with various medical implications. There is considerable literature pointing to a role for cell communication in a wide variety of illnesses.

Cyclooxygenase-2 is involved in HIV-1 Tat-induced inflammatory responses in the brain

Cyclooxygenase (COX)-2, a rate-limiting enzyme for prostanoid synthesis, can be involved in inflammatory-mediated cytotoxicity. Although the contribution of COX-2 to peripheral inflammation is well understood, its role in brain inflammation is not fully recognized. In particular, COX-2 involvement in inflammatory responses induced by HIV proteins in the central nervous system is not known. Therefore, the present study focused on COX-2 expression and its role in modulating the expression of brain inflammatory-related genes following exposure to the HIV-1 transactivating protein Tat. Intrahippocampal injections of Tat induced dose-dependent upregulation of COX-2 mRNA and protein levels in C57BL/6 mice. COX-2 immunoreactivity was primarily localized in microglial cells and astrocytes. Tat-induced COX-2 expression was partially prevented by pyrrolidine dithiocarbamate, a potent antioxidant and an inhibitor of the transcription factor, nuclear factor kappaB. Most importantly, administration of the COX-2 inhibitor NS-398 attenuated Tat-mediated upregulation of mRNA and protein expression of inflammatory mediators, such as monocyte chemoattractant protein-1, interleukin-1beta, tumor necrosis factor-alpha, and inducible nitric oxide synthase. Moreover, treatment with NS-398 significantly attenuated Tat-induced activation of microglial cells. These results provide evidence that COX-2 overexpression can modulate induction of brain inflammatory mediators in response to HIV-1 Tat protein. Such alterations may play an important role in the development of brain inflammatory reactions in HIV-infected patients and contribute to the development of neurological complications in the course of HIV-1 infection.

HIV-1 neuropathogenesis: glial mechanisms revealed through substance abuse

Neuronal dysfunction and degeneration are ultimately responsible for the neurocognitive impairment and dementia manifest in neuroAIDS. Despite overt neuronal pathology, HIV-1 does not directly infect neurons; rather, neuronal dysfunction or death is largely an indirect consequence of disrupted glial function and the cellular and viral toxins released by infected glia. A role for glia in HIV-1 neuropathogenesis is revealed in experimental and clinical studies examining substance abuse-HIV-1 interactions. Current evidence suggests that glia are direct targets of substance abuse and that glia contribute markedly to the accelerated neurodegeneration seen with substance abuse in HIV-1 infected individuals. Moreover, maladaptive neuroplastic responses to chronic drug abuse might create a latent susceptibility to CNS disorders such as HIV-1. In this review, we consider astroglial and microglial interactions and dysfunction in the pathogenesis of HIV-1 infection and examine how drug actions in glia contribute to neuroAIDS.

TAT-mediated intracellular delivery of purine nucleoside phosphorylase corrects its deficiency in mice

Defects in purine nucleoside phosphorylase (PNP) enzyme activity result in abnormal nucleoside homeostasis, severe T cell immunodeficiency, neurological dysfunction, and early death. Protein transduction domain (PTD) can transfer molecules into cells and may help restore PNP activity in cases of PNP deficiency. However, long-term use of PTD to replace enzymes in animal models or patients has not previously been described. We fused human PNP to the HIV-TAT PTD and found that the fusion with TAT changed the retention and distribution of PNP in PNP-deficient mice. TAT induced rapid intracellular delivery of PNP into tissues, including the brain, prevented urinary excretion of PNP, and protected PNP from neutralizing antibodies, resulting in significant extension of the enzyme's biological activity in vivo. Frequent TAT-PNP injections in PNP-deficient mice corrected the metabolic disorder and immune defects with no apparent toxicity. TAT-PNP remained effective over 24 weeks of treatment, resulting in continued improvement in immune function and extended survival. Our data demonstrate that TAT changes the properties of PNP in vivo and that long-term intracellular delivery of PNP by TAT corrects PNP deficiency in mice. We provide evidence to promote further use of PTD to treat diseases that require repeated intracellular enzyme or protein delivery.

Inhibition of tumor necrosis factor-alpha signaling prevents human immunodeficiency virus-1 protein Tat and methamphetamine interaction

Our previous studies demonstrated that the psychostimulant methamphetamine (MA) and the human immunodeficiency virus-1 (HIV-1) protein Tat interacted to cause enhanced dopaminergic neurotoxicity. The present study examined whether tumor necrosis factor-alpha (TNF-alpha) mediates the interaction between Tat and MA. In Sprague-Dawley rats, injections of Tat caused a small but significant increase in striatal TNF-alpha level, whereas MA resulted in no change. The increase in TNF-alpha induced by Tat + MA was not significantly different from that induced by Tat alone. Temporal analysis of TNF-alpha levels revealed a 50-fold increase 4 h after Tat administration. In C57BL/6 mice, Tat + MA induced a 50% decline in striatal dopamine levels, which was significantly attenuated in mice lacking both receptors for TNF-alpha. TNF-alpha synthesis inhibitors significantly attenuated Tat + MA neurotoxicity in hippocampal neuronal culture. The results suggest that Tat-induced elevation of TNF-alpha may predispose the dopaminergic terminals to subsequent damage by MA.

Interaction of HIV Tat and matrix metalloproteinase in HIV neuropathogenesis: a new host defense mechanism

Tat, the HIV transactivating protein, and matrix metalloproteinases (MMPs), a family of extracellular matrix (ECM) endopeptidases, have been implicated in the pathogenesis of HIV-associated dementia. However, the possibility that MMPs interact with viral proteins has remained unexplored. We therefore treated mixed human fetal neuronal cultures with recombinant Tat and select MMPs. Neurotoxicity was determined by measuring mitochondrial membrane potential and neuronal cell death. Previous studies have shown that Tat and MMP independently cause neurotoxicity. Surprisingly, we found the combination of Tat and MMP produced significant attenuation of neurotoxicity. To determine whether there was a physical interaction between Tat and MMP, we used protein electrophoresis and Western blot techniques, and found that MMP-1 can degrade Tat. This effect was blocked by MMP inhibitors. Furthermore, MMP-1 decreased Tat-mediated transactivation of the HIV long terminal repeat region, and this functionality was restored when MMP-1 activity was inhibited. These results suggest that the decrease in Tat-induced neurotoxicity and HIV transactivation is due to Tat's enzymatic cleavage by MMP-1. The direct interaction of human MMPs with viral proteins has now been demonstrated, with resultant modulation of Tat-mediated neurotoxicity and transactivation. This study elucidates a unique viral-host interaction that may serve as an innate host defense mechanism.

Neuroimmunity and the blood-brain barrier: molecular regulation of leukocyte transmigration and viral entry into the nervous system with a focus on neuroAIDS

HIV infection of the central nervous system (CNS) can result in neurologic dysfunction with devastating consequences in a significant number of individuals with AIDS. Two main CNS complications in individuals with HIV are encephalitis and dementia, which are characterized by leukocyte infiltration into the CNS, microglia activation, aberrant chemokine expression, blood-brain barrier (BBB) disruption, and eventual damage and/or loss of neurons. One of the major mediators of NeuroAIDS is the transmigration of HIV-infected leukocytes across the BBB into the CNS. This review summarizes new key findings that support a critical role of the BBB in regulating leukocyte transmigration. In addition, we discuss studies on communication among cells of the immune system, BBB, and the CNS parenchyma, and suggest how these interactions contribute to the pathogenesis of NeuroAIDS. We also describe some of the animal models that have been used to study and characterize important mechanisms that have been proposed to be involved in HIV-induced CNS dysfunction. Finally, we review the pharmacologic interventions that address neuroinflammation, and the effect of substance abuse on HIV-1 related neuroimmunity.

Involvement of cytokines in human immunodeficiency virus-1 protein Tat and methamphetamine interactions in the striatum

Human immunodeficiency virus-1 (HIV-1) infection of the brain causes elevation in pro-inflammatory cytokines and inflammatory changes in the striatum. HIV-1-infected individuals who also abuse drugs including the psychostimulant methamphetamine (MA) develop more severe encephalitis and neuronal damage compared to HIV-1-infected patients who do not abuse drugs. In previous studies, we demonstrated that the HIV-1 protein Tat and MA interacted to cause enhanced loss of dopamine in the rat striatum via the destruction of dopaminergic terminals. Since both Tat and MA activate glia and induce cytokine production, we investigated the role of cytokines in the synergistic neurotoxicity induced by Tat and MA using cytokine arrays. Significant increases in monocyte chemotactic protein (MCP-1), interleukin-1 alpha (IL-1alpha) and tissue inhibitor of metalloproteinase-1 (TIMP-1) levels were noted 4 h following Tat + MA treatment compared to saline, Tat or MA. MCP-1 and TIMP-1 levels remained elevated 16 h after Tat + MA compared to saline or MA but were not different from the Tat-treated group at this time point. Weak, but significant elevations in cytokine-induced neutrophil chemoattractant-3 (CINC-3), ciliary neurotrophic factor (CNTF) and macrophage inflammatory protein-3 alpha (MIP-3alpha) were also noted with Tat + MA. The interaction of Tat and MA was prevented in mice genetically deficient in MCP-1 with a consequent attenuation of Tat + MA neurotoxicity. Our findings suggest that HIV-1 infection with concurrent drug abuse might profoundly increase chemokine levels in the striatum resulting in enhanced damage to the dopaminergic system.

Methamphetamine and human immunodeficiency virus protein Tat synergize to destroy dopaminergic terminals in the rat striatum

Dysfunction of the dopaminergic system accompanied by loss of dopamine in the striatum is a major feature of human immunodeficiency virus-1-associated dementia. Previous studies have shown that human immunodeficiency virus-1-associated dementia patients with a history of drug abuse have rapid neurological progression, prominent psychomotor slowing, more severe encephalitis and more severe dendritic and neuronal damage in the frontal cortex compared with human immunodeficiency virus-1-associated dementia patients without a history of drug abuse. In a previous study, we showed that methamphetamine and human immunodeficiency virus-1 protein Tat interact to produce a synergistic decline in dopamine levels in the rat striatum. The present study was carried out to understand the underlying cause for the loss of dopamine. Male Sprague-Dawley rats were administered saline, methamphetamine, Tat or Tat followed by methamphetamine 24 h later. Two and seven days later the animals were killed and tissue sections from striatum were processed for silver staining to examine terminal degeneration while sections from striatum and substantia nigra were processed for tyrosine hydroxylase immunoreactivity. Striatal tissue was also analyzed by Western blotting for tyrosine hydroxylase protein levels. Compared with controls, methamphetamine+Tat-treated animals showed extensive silver staining and loss of tyrosine hydroxylase immunoreactivity and protein levels in the ipsilateral striatum. There was no apparent loss of tyrosine hydroxylase in the substantia nigra. Markers for oxidative stress were significantly increased in striatal synaptosomes from Tat+methamphetamine group compared with controls. The results indicate that methamphetamine and Tat interact to produce an enhanced injury to dopaminergic nerve terminals in the striatum with sparing of the substantia nigra by a mechanism involving oxidative stress. These findings suggest a possible mode of interaction between methamphetamine and human immunodeficiency virus-1 infection to produce enhanced dopaminergic neurotoxicity in human immunodeficiency virus-1 infected/methamphetamine-abusing patients.

HIV-1 Tat protein-induced alterations of ZO-1 expression are mediated by redox-regulated ERK 1/2 activation

HIV-1 Tat protein plays an important role in inducing monocyte infiltration into the brain and may alter the structure and functions of the blood-brain barrier (BBB). The BBB serves as a frontline defense system, protecting the central nervous system from infected monocytes entering the brain. Therefore, the aim of the present study was to examine the mechanisms of Tat effect on the integrity of the BBB in the mouse brain. Tat was injected into the right hippocampi of C57BL/6 mice and expression of tight junction protein zonula occludens-1 (ZO-1) was determined in control and treated mice. Tat administration resulted in decreased mRNA levels of ZO-1 and marked disruption of ZO-1 continuity. These changes were associated with accumulation of inflammatory cells in brain tissue of Tat-treated mice. Further experiments indicated that Tat-mediated alterations of redox-related signaling may be responsible for decreased ZO-1 expression. Specifically, injections with Tat resulted in activation of extracellular signal-regulated kinase 1/2 (ERK 1/2) and pretreatment with U 0126, a specific inhibitor of ERK kinase, effectively ameliorated the Tat-induced diminished ZO-1 levels. In addition, administration of N-acetylcysteine (NAC), a precursor of glutathione and a potent antioxidant, attenuated both Tat-induced ERK 1/2 activation and alterations in ZO-1 expression. These results indicate that Tat-induced oxidative stress can play an important role in affecting the integrity of the BBB through the ERK 1/2 pathway.

Mechanisms of the blood-brain barrier disruption in HIV-1 infection

(1) Alterations of brain microvasculature and the disruption of the blood-brain barrier (BBB) integrity are commonly associated with human immunodeficiency virus type 1 (HIV-1) infection. These changes are most frequently found in human immunodeficiency virus-related encephalitis (HIVE) and in human immunodeficiency virus-associated dementia (HAD). (2) It has been hypothesized that the disruption of the BBB occurs early in the course of HIV-1 infection and can be responsible for HIV-1 entry into the CNS. (3) The current review discusses the mechanisms of injury to brain endothelial cells and alterations of the BBB integrity in HIV-infection with focus on the vascular effects of HIV Tat protein. In addition, this review describes the mechanisms of the BBB disruption due to HIV-1 or Tat protein interaction with selected risk factors for HIV infection, such as substance abuse and aging.

MK-801 and dextromethorphan block microglial activation and protect against methamphetamine-induced neurotoxicity

Methamphetamine causes long-term toxicity to dopamine nerve endings of the striatum. Evidence is emerging that microglia can contribute to the neuronal damage associated with disease, injury, or inflammation, but their role in methamphetamine-induced neurotoxicity has received relatively little attention. Lipopolysaccharide (LPS) and the neurotoxic HIV Tat protein, which cause dopamine neuronal toxicity after direct infusion into brain, cause activation of cultured mouse microglial cells as evidenced by increased expression of intracellular cyclooxygenase-2 and elevated secretion of tumor necrosis factor-alpha. MK-801, a non-competitive NMDA receptor antagonist that is known to protect against methamphetamine neurotoxicity, prevents microglial activation by LPS and HIV Tat. Dextromethorphan, an antitussive agent with NMDA receptor blocking properties, also prevents microglial activation. In vivo, MK-801 and dextromethorphan reduce methamphetamine-induced activation of microglia in striatum and they protect dopamine nerve endings against drug-induced nerve terminal damage. The present results indicate that the ability of MK-801 and dextromethorphan to protect against methamphetamine neurotoxicity is related to their common property as blockers of microglial activation.

HIV-Tat protein induces P-glycoprotein expression in brain microvascular endothelial cells

Among the different factors which can contribute to CNS alterations associated with HIV infection, Tat protein is considered to play a critical role. Evidence indicates that Tat can contribute to brain vascular pathology through induction of endothelial cell activation. In the present study, we hypothesized that Tat can affect expression of P-glycoprotein (P-gp) in brain microvascular endothelial cells (BMEC). P-gp is an ATP-dependent cellular efflux transporter which is involved in the removal of specific non-polar molecules, including drugs used for highly active antiretroviral therapy (HAART). Treatment of BMEC with Tat(1-72) resulted in P-gp overexpression both at mRNA and protein levels. These alterations were confirmed in vivo in brain vessels of mice injected with Tat(1-72) into the hippocampus. Furthermore, pre-treatment of BMEC with SN50, a specific NF-kappaB inhibitor, protected against Tat(1-72)-stimulated expression of mdr1a gene, i.e. the gene which encodes for P-gp in rodents. Tat(1-72)-mediated changes in P-gp expression were correlated with increased rhodamine 123 efflux, indicating the up-regulation of transporter functions of P-gp. These results suggest that Tat-induced overexpression of P-gp in brain microvessels may have significant implications for the development of resistance to HAART and may be a contributing factor for low efficacy of HAART in the CNS.

Cytotoxic effects of exposure to the human immunodeficiency virus type 1 protein Tat in the hippocampus are enhanced by prior ethanol treatment

BACKGROUND

Long-term ethanol exposure leads to increases in the expression and/or sensitivity of NMDA-type glutamate receptors, effects that may contribute to the development of cytotoxicity in the brain. The human immunodeficiency virus 1 (HIV-1) transcription factor Tat is one of many viral proteins that may contribute to the development of HIV-associated dementia (HAD) by indirectly or directly promoting excess function of NMDA receptors. Thus, these studies examined the hypothesis that long-term ethanol pre-exposure would sensitize the hippocampus to Tat-induced cytotoxicity in an NMDA receptor-dependent manner.

METHODS

Organotypic slice cultures of rat hippocampus were exposed to a recombinant 86-amino acid form of Tat (Tat1-86) or a Tat deletion mutant devoid of amino acids 31 to 61 (TatDelta31-61; 0.1-100 nM) for 24 hr alone or during withdrawal from 10 days of ethanol exposure (50 mM in culture medium). Additional cultures were exposed to NMDA (5 microM) or the NMDA receptor channel blocker MK-801 (1 microM) during these treatments. Cellular injury in the CA1, CA3, and dentate gyrus regions of slice cultures was assessed by microscopy of propidium iodide fluorescence.

RESULTS

Twenty-four hours of withdrawal from ethanol exposure did not produce overt cellular injury in any region of slice cultures. However, NMDA-induced toxicity was markedly increased in ethanol-pre-exposed cultures, an effect prevented by MK-801 (1 microM) coexposure. Treatment of cultures with Tat1-86 alone (> or = 0.1 nM) produced modest toxicity in each region of hippocampal cultures that was also blocked by MK-801 coexposure. In contrast, exposure to TatDelta31-61 did not alter propidium iodide fluorescence. Exposure of cultures to Tat1-86 (> or = 0.1 nM) during ethanol withdrawal resulted in a marked potentiation of Tat's toxic effects in each region of slice cultures, particularly the CA1 region. This potentiation of Tat neurotoxicity was significantly attenuated by coexposure of cultures to MK-801 (1 microM).

CONCLUSIONS

These results indicate that long-term ethanol exposure sensitizes the hippocampus to the cytotoxic effects of Tat in an NMDA receptor-dependent manner. This may suggest that HIV-1-positive individuals who are alcohol dependent possess a heightened risk for the development of HAD. Furthermore, the NMDA receptor, particularly allosteric modulatory sites such as polyamine-sensitive sites, may be a therapeutic target to be investigated in the treatment of HAD.

Proinflammatory synergism of ethanol and HIV-1 Tat protein in brain tissue

Human immunodeficiency virus type 1 (HIV-1) Tat protein is a potent transactivator of viral replication. It is actively released from HIV-infected cells and has been shown to induce cell injury effects. Alcohol abuse is a risk factor of HIV infection and we hypothesize that alcohol and Tat may interact in an additive or synergistic fashion to influence molecular processes which can contribute to their toxic effects. To study this possibility, we investigated the effects of two intraperitoneal injections of ethanol (EtOH, 3 g/kg each, 16 h apart) and a single intracerebral injection of Tat (25 microg/microl into the right hippocampus, injected 12 h after the first EtOH injection) on generation of cellular oxidative stress, DNA binding activity of redox-responsive transcription factors, and induction of inflammatory genes in the hippocampus and corpus striatum of mouse brain. As compared to control animals, treatment with EtOH plus Tat resulted in increased production of reactive oxygen species in both brain regions. In addition, DNA binding activities of nuclear factor-kappaB (NF-kappaB) and CREB in both brain regions and SP-1 in the hippocampus were more pronounced in mice injected with Tat plus EtOH as compared to the effects of Tat or EtOH alone. Among studied inflammatory genes, induction of IL-1beta and MCP-1 was potentiated in animals injected with EtOH plus Tat. These results indicate that Tat and EtOH can cross-amplify their cellular effects, leading to alterations of redox-regulated inflammatory pathways in the brain. Such potentiation of proinflammatory stimulation may further contribute to CNS pathology in HIV-infected patients who are alcohol abusers.

Delivery of bioactive molecules into the cell: the Trojan horse approach

In recent years, vast amounts of data on the mechanisms of neural de- and regeneration have accumulated. However, only in disproportionally few cases has this led to efficient therapies for human patients. Part of the problem is to deliver cell death-averting genes or gene products across the blood-brain barrier (BBB) and cellular membranes. The discovery of Antennapedia (Antp)-mediated transduction of heterologous proteins into cells in 1992 and other "Trojan horse peptides" raised hopes that often-frustrating attempts to deliver proteins would now be history. The demonstration that proteins fused to the Tat protein transduction domain (PTD) are capable of crossing the BBB may revolutionize molecular research and neurobiological therapy. However, it was only recently that PTD-mediated delivery of proteins with therapeutic potential has been achieved in models of neural degeneration in nerve trauma and ischemia. Several groups have published the first positive results using protein transduction domains for the delivery of therapeutic proteins in relevant animal models of human neurological disorders. Here, we give an extensive review of peptide-mediated protein transduction from its early beginnings to new advances, discuss their application, with particular focus on a critical evaluation of the limitations of the method, as well as alternative approaches. Besides applications in neurobiology, a large number of reports using PTD in other systems are included as well. Because each protein requires an individual purification scheme that yields sufficient quantities of soluble, transducible material, the neurobiologist will benefit from the experiences of other researchers in the growing field of protein transduction.

Multiple actions of the human immunodeficiency virus type-1 Tat protein on microglial cell functions

The human immunodeficiency virus type-1 (HIV-1) regulatory protein Tat is produced in the early phase of infection and is essential for virus replication. Together with other viral products, Tat has been implicated in the pathogenesis of HIV-1-associated dementia (HAD). As HIV-1 infection in the brain is very limited and macrophage/microglial cells are the only cellular type productively infected by the virus, it has been proposed that many of the viral neurotoxic effects are mediated by microglial products. We and others have shown that Tat affects the functional state of microglial cells, supporting the hypothesis that activated microglia play a role in the neuropathology associated with HIV-1 infection. This review describes the experimental evidence indicating that Tat stimulates microglia to synthesize potentially neurotoxic molecules, including proinflammatory cytokines and free radicals, and interferes with molecular mechanisms controlling cAMP levels, intracellular [Ca2+], and ion channel expression.

Physiological and behavioral effects of methamphetamine in a mouse model of endotoxemia: a preliminary study

We investigated the effects of methamphetamine (METH) on core body temperature (Tb) and motor activity (MA) with or without exposure to a peripheral immune challenge. Mice were exposed to an escalating METH treatment and then to a METH treatment known to cause neurotoxicity (binge METH treatment). This was followed by a challenge with lipopolysaccharide (LPS). Three days later, METH and saline-treated control groups were challenged with an acute test dose of METH (METH test). Animals exposed to the escalating METH treatment exhibited a significant increase in Tb only after the initial exposure to METH (Day 1) and following the METH test (Day 7). The hyperthermic effect produced by the METH test (Day 7) was reduced in mice previously exposed to combined exposure to binge METH and LPS treatments. The escalating METH treatment produced MA sensitization to the METH test. Animals treated with the binge METH, LPS injection or both treatments combined prevented MA sensitization to the METH test. These findings suggest that induction of peripheral endotoxemia in animals with a history of METH reduced the hyperthermic response to a subsequent challenge with METH.

HIV-1 Tat protein upregulates inflammatory mediators and induces monocyte invasion into the brain

Impaired inflammatory functions may be critical factors in the mechanisms by which HIV-1 enters the CNS. Evidence indicates that a viral gene product, the protein Tat, can markedly contribute to these effects. In the present study we tested the hypothesis that Tat can upregulate the expression of inflammatory cytokines and adhesion molecules and facilitate the entry of monocytes into the brain. Expression of inflammatory mediators such as monocyte chemoattractant protein-1 (MCP-1), tumor necrosis factor-alpha (TNF-alpha), vascular cell adhesion molecule-1 (VCAM-1), and intercellular adhesion molecule-1 (ICAM-1) was assessed in C57BL/6 mice injected with Tat(1-72) into the right hippocampus. In the Tat(1-72)-injected groups, mRNA and protein levels of MCP-1, TNF-alpha, VCAM-1, and ICAM-1 were markedly elevated compared to those in control animals. The most pronounced changes were observed in and around the injected hippocampus. Double-labeling immunohistochemistry demonstrated that inflammatory proteins were primarily expressed in activated microglial cells and perivascular cells. In addition, astrocytes and endothelial cells were susceptible to Tat(1-72)-induced inflammatory responses. These changes were associated with a substantial infiltration of monocytes into the brain. These data demonstrate that intracerebral administration of Tat can induce profound proinflammatory effects in the brain, leading to monocyte infiltration.

Patterns of Selective Neuronal Damage in Methamphetamine-User AIDS Patients

The risk for HIV infection attributable to methamphetamine (METH) use continues to increase. The combined effect of HIV and METH in the pathogenesis of HIV encephalitis (HIVE) is unclear, however. To better understand the neuropathology associated with HIV and METH use, the patterns of neurodegeneration were assessed in HIV-positive METH users and in HIV-positive non-METH users. Patients in the study met criteria for inclusion and received neuromedical and postmortem neuropathologic examinations. Immunocytochemical and polymerase chain reaction analyses were performed to determine brain HIV levels and to exclude the presence of other viruses. METH-using patients with HIVE showed significantly lower gp41 scores and less severe forms of encephalitis but a higher frequency of ischemic events, a more pronounced loss of synaptophysin immunoreactivity, and a more severe microglial reaction than HIVE non-METH users. Furthermore, in METH-using patients with HIVE, extensive loss of calbindin (CB)-immunoreactive interneurons displaying phylopodial neuritic processes suggestive of aberrant sprouting was observed. Taken together, these studies indicate that the combined effects of METH and HIV selectively damage CB immunoreactive nonpyramidal neurons. In combination, METH and HIV may increase neuronal cell injury and death, thereby enhancing brain metabolic disturbances observed in clinical populations of HIV-positive METH abusers.