Biomedical subjects

William F Maragos

Publications and source records attributed to William F Maragos.

14 recordsLinked to original sources

PubMed2006

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.

AIDS Dementia Complex↗

PubMed2006

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.

AIDS Dementia Complex↗

PubMed2006

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.

Analysis of Variance↗

PubMed2006

Human immunodeficiency virus-1 protein tat and methamphetamine interactions.

The human immunodeficiency virus-1 (HIV-1) affects the central nervous system (CNS) in approximately 30% of infected individuals and basal ganglia structures seem to be most affected. The HIV-1-transactivating protein, Tat, has been suggested to be pathogenically relevant in HIV-1-induced neuronal injury. The abuse of methamphetamine (METH), which is great among this patient population, also affects the basal ganglia, causing degeneration of dopaminergic terminals. In previous studies, we demonstrated that coexposure to these two toxins caused a synergistic loss of striatal dopamine and binding to the dopamine transporter (DAT), suggesting a loss of dopamine terminals. Because the loss of dopamine and DAT, however, do not necessarily reflect dopamine terminal degeneration, we have used silver staining and TH immunohistochemistry to further examine this issue. We have also examined the glial reaction using GFAP as a marker of astrocyte activation and OX-42 as a marker of activated microglia. Lastly, we have begun to explore the mechanism of synergy by investigating the role that the cytokine TNF-alpha might play in Tat + METH synergy. Our data indicate that the synergistic loss of dopamine is likely the result of dopamine terminal degeneration. This injury is not a direct result of the number of activated glia but does involve TNF-alpha.

Animals↗

PubMed2005

The mitochondrial uncoupler 2,4-dinitrophenol attenuates tissue damage and improves mitochondrial homeostasis following transient focal cerebral ischemia.

Ischemic stroke is caused by acute neuronal degeneration provoked by interruption of cerebral blood flow. Although the mechanisms contributing to ischemic neuronal degeneration are myriad, mitochondrial dysfunction is now recognized as a pivotal event that can lead to either necrotic or apoptotic neuronal death. Lack of suitable 'upstream' targets to prevent loss of mitochondrial homeostasis has, so far, restricted the development of mechanistically based interventions to promote neuronal survival. Here, we show that the uncoupling agent 2,4 dinitrophenol (DNP) reduces infarct volume approximately 40% in a model of focal ischemia-reperfusion injury in the rat brain. The mechanism of protection involves an early decrease in mitochondrial reactive oxygen species formation and calcium uptake leading to improved mitochondrial function and a reduction in the release of cytochrome c into the cytoplasm. The observed effects of DNP were not associated with enhanced cerebral perfusion. These findings indicate that compounds with uncoupling properties may confer neuroprotection through a mechanism involving stabilization of mitochondrial function.

2,4-Dinitrophenol↗

PubMed2005

Enhanced toxicity to the catecholamine tyramine in polyglutamine transfected SH-SY5Y cells.

Huntington's disease (HD) is a progressive neurodegenerative disorder, of which the pathogenesis is not completely understood. In patients with Huntington's disease, there is a mutation in the gene encoding the protein huntingtin, which results in an expanded polyglutamine sequence leading to degeneration of the basal ganglia. There is mounting evidence that metabolism of the transmitter dopamine by the enzyme monoamine oxidase may contribute to striatal damage in mitochondrial toxin-induced models of HD. In this study, we have examined the role of the catecholamine tyramine in neural SH-SY5Y cells transfected with normal and expanded polyglutamine repeat numbers. Our findings demonstrate that cells containing a pathological number of polyglutamines are more sensitive to tyramine than cells with a non-pathological number. Tyramine-induced cell death was attenuated by MAO inhibitors as well as with catalase and the iron chelator deferoxamine, suggesting that H202 might mediate the observed toxicity. These observations support the notion that the metabolism of dopamine plays a role in neuron death in Huntington's disease.

Catalase↗

PubMed2005

The uncoupling agent 2,4-dinitrophenol improves mitochondrial homeostasis following striatal quinolinic acid injections.

It is now generally accepted that excitotoxic cell death involves bioenergetic failure resulting from the cycling of Ca2+ and the generation of reactive oxygen species (ROS) by mitochondria. Both Ca2+ cycling and ROS formation by mitochondria are dependent on the mitochondrial membrane potential (Deltapsi(m)) that results from the proton gradient that is generated across the inner membrane. Mitochondrial uncoupling refers to a condition in which protons cross the inner membrane back into the matrix while bypassing the ATP synthase. As a consequence of this "short-circuit," there is a reduction in Deltapsi(m). We have previously demonstrated that animals treated with the classic uncoupling agent 2,4-dinitrophenol (DNP) show significant protection against brain damage following striatal injections of the NMDA agonist quinolinic acid (QA). In an effort to elucidate the mechanism of neuroprotection, we have assessed the effects of DNP on several parameters of mitochondrial function caused by QA. The results presented herein demonstrate that treatment with DNP attenuates QA-induced increases in mitochondrial Ca2+ levels and ROS formation and also improves mitochondrial respiration. Our findings indicate that DNP may confer protection against acute brain injury involving excitotoxic pathways by mechanisms that maintain mitochondrial function.

2,4-Dinitrophenol↗

PubMed2004

Striatal damage and oxidative stress induced by the mitochondrial toxin malonate are reduced in clorgyline-treated rats and MAO-A deficient mice.

Intrastriatal administration of the succinate dehydrogenase (SDH) inhibitor malonate produces neuronal injury by a "secondary excitotoxic" mechanism involving the generation of reactive oxygen species (ROS). Recent evidence indicates dopamine may contribute to malonate-induced striatal neurodegeneration; infusion of malonate causes a pronounced increase in extracellular dopamine and dopamine deafferentation attenuates malonate toxicity. Inhibition of the catabolic enzyme monoamine oxidase (MAO) also attenuates striatal lesions induced by malonate. In addition to forming 3,4-dihydroxyphenylacetic acid, metabolism of dopamine by MAO generates H2O2, suggesting that dopamine metabolism may be a source of ROS in malonate toxicity. There are two isoforms of MAO, MAO-A and MAO-B. In this study, we have investigated the role of each isozyme in malonate-induced striatal injury using both pharmacological and genetic approaches. In rats treated with either of the specific MAO-A or -B inhibitors, clorgyline or deprenyl, respectively, malonate lesion volumes were reduced by 30% compared to controls. In knock-out mice lacking the MAO-A isoform, malonate-induced lesions were reduced by 50% and protein carbonyls, an index ROS formation, were reduced by 11%, compared to wild-type animals. In contrast, mice deficient in MAO-B showed highly variable susceptibility to malonate toxicity precluding us from determining the precise role of MAO-B in this form of brain damage. These findings indicate that normal levels of MAO-A participate in expression of malonate toxicity by a mechanism involving oxidative stress.

Animals↗

PubMed2004

The mitochondrial uncoupling agent 2,4-dinitrophenol improves mitochondrial function, attenuates oxidative damage, and increases white matter sparing in the contused spinal cord.

The purpose of this study was to investigate the potential neuroprotective efficacy of the mitochondrial uncoupler 2,4-dinitrophenol (DNP) in rats following a mild to moderate spinal cord contusion injury. Animals received intraperitoneal injections of vehicle (DMSO) or 5 mg/mL of DNP prior to injury. Twenty-four hours following surgery, mitochondrial function was assessed in mitochondria isolated from spinal cord synaptosomes. In addition, synaptosomes were used to measure indicators of reactive oxygen species formation, lipid peroxidation, and protein oxidation. Relative to vehicle-treated animals, pretreatment with DNP maintained mitochondrial bioenergetics and significantly decreased reactive oxygen species levels, lipid peroxidation, and protein carbonyl content following spinal cord injury. Furthermore, pretreatment with DNP significantly increased the amount of remaining white matter at the injury epicenter 6 weeks after injury. These results indicate that treatment with mitochondrial uncoupling agents may provide a novel approach for the treatment of secondary injury following spinal cord contusion.

2,4-Dinitrophenol↗

PubMed2004

Mitochondrial uncoupling as a potential therapeutic target in acute central nervous system injury.

Mitochondrial dysfunction, resulting from the disruption of calcium homeostasis and the generation of toxic reactive oxygen species, is a central process leading to neuronal injury and death following acute CNS insults. Interventions aimed at preventing disturbances in mitochondrial function have therefore become targets of intense investigation. Mitochondrial uncoupling is a condition in which electron transport is disconnected from the production of ATP. As a consequence, there is a decrease in the mitochondrial membrane potential, which can temporarily decrease calcium influx and attenuate free radical formation. The potential use of pharmacological agents with uncoupling properties may provide a novel therapeutic approach for the treatment of acute neuronal injury.

Acute Disease↗

PubMed2003

HIV-1 protein Tat potentiation of methamphetamine-induced decreases in evoked overflow of dopamine in the striatum of the rat.

HIV-1 infection of the brain can lead to the development of clinical syndromes reminiscent of Parkinson's disease, suggesting that HIV infection may damage nigrostriatal dopamine (DA) neurons. Although the responsible mechanisms have not been well defined, neurotoxic viral proteins, such as Tat, released from infected cells may be involved. Drug abuse is a major risk factor for contracting HIV infection. Methamphetamine (METH), a psychostimulant with high abuse potential, may also be toxic to brain DA neurons. Thus, the combination of METH abuse and HIV infection may lead to substantial alterations in DA neuron functioning. The present experiments examined how Tat, alone and with METH, affects DA release in the striatum. Male rats were given an intrastriatal injection of Tat (25 micro g) or vehicle 24 h before treatment with saline or neurotoxic doses of METH. Seven days later microdialysis studies were carried out to measure potassium- and amphetamine-evoked overflow of DA from the striatum. The Tat treatment alone led to no change in potassium-evoked overflow of DA, a 20% decrease in amphetamine-evoked overflow of DA, and a 16% decrease in striatal DA content. The METH alone led to a 37-42% decrease in striatal DA overflow and content. The combined treatment with Tat and METH led to significantly greater 70-78% decreases in striatal DA overflow and content. These results indicate that Tat enhances METH-induced reductions in striatal DA release and content, possibly in a synergistic manner, and suggest that METH abusers infected with HIV may be at increased risk for basal ganglia dysfunction.

Animals↗

PubMed2003

Pre- or post-treatment with the mitochondrial uncoupler 2,4-dinitrophenol attenuates striatal quinolinate lesions.

We have examined the neuroprotective efficacy of the mitochondrial uncoupler 2,4-dinitrophenol (DNP) in animals receiving striatal injections of the neurotoxin quinolinic acid. Animals administered DNP either 1 h before or 3 h following QA infusion developed lesions that were 25% smaller than control animals. Animals treated with the DNP analogue 2,4,6-trinitrophenol, which does not possess uncoupling activity in intact mitochondria, showed no neuroprotection. These results indicate that DNP, and other compounds that diminish the mitochondrial membrane potential, might provide a novel approach to the treatment of acute neurological injury.

2,4-Dinitrophenol↗

PubMed2002

Mitochondrial toxin inhibition of [(3)H]dopamine uptake into rat striatal synaptosomes.

Administration of the mitochondrial inhibitors malonate and 3-nitropropionic acid (3-NP) to rats provides useful models of Huntington's disease. Exposure to these inhibitors has been shown to result in increased extracellular concentrations of striatal dopamine (DA), which is neurotoxic at high concentrations. The cause of this increase is unknown. The purpose of this study was to determine whether mitochondrial inhibition alters dopamine transporter (DAT) function. Striatal synaptosomes were incubated in the presence of several structurally unrelated inhibitors of mitochondrial Complexes I, II, and IV, and [(3)H]DA uptake was measured. Although all of the toxins inhibited [(3)H]DA uptake, there was a large variation in their inhibitory potencies, the rank order being rotenone>>cyanide>azide>3-NP>>malonate. Examination of the kinetic parameters of [(3)H]DA uptake revealed that inhibition was due to a reduction in maximum velocity (V(max)), with no change in affinity (K(m)). The addition of either ATP or of ADP plus P(i) to synaptosomes treated with 3-NP, or of the reactive oxygen species spin trap alpha-phenyl-N-tert-butyl nitrone to synaptosomes exposed to either malonate or cyanide failed to prevent mitochondrial toxin-induced inhibition of DAT function. The lack of effect of high energy substrates or of a free radical scavenger suggests that the mechanism by which extracellular DA is increased by several mitochondrial toxins involves factors other than mitochondrial ATP production or oxidative stress. Taken together, the results suggest that one mechanism whereby mitochondrial toxins increase extracellular concentrations of DA is via interaction with the DAT at a site other than the substrate site, i.e. noncompetitive inhibition of the DAT.

Animals↗

PubMed2002

Human immunodeficiency virus-1 Tat protein and methamphetamine interact synergistically to impair striatal dopaminergic function.

The human immunodeficiency virus (HIV)-1 transactivating protein Tat may be pathogenically relevant in HIV-1-induced neuronal injury. The abuse of methamphetamine (MA), which is associated with behaviors that may transmit HIV-1, may damage dopaminergic afferents to the striatum. Since Tat and MA share common mechanisms of injury, we examined whether co-exposure to these toxins would lead to enhanced dopaminergic toxicity. Animals were treated with either saline, a threshold dose of MA, a threshold concentration of Tat injected directly into the striatum, or striatal injections of Tat followed by exposure to MA. Threshold was defined as the highest concentration of toxin that would not result in a significant loss of striatal dopamine levels. One week later, MA-treated animals demonstrated a 7% decline in striatal dopamine levels while Tat-treated animals showed an 8% reduction. Exposure to both MA + Tat caused an almost 65% reduction in striatal dopamine. This same treatment caused a 56% reduction in the binding capacity to the dopamine transporter. Using human fetal neurons, enhanced toxicity was also observed when cells were exposed to both Tat and MA. Mitochondrial membrane potential was disrupted and could be prevented by treatment with antioxidants. This study demonstrates that the HIV-1 'virotoxin' Tat enhances MA-induced striatal damage and suggests that HIV-1-infected individuals who abuse MA may be at increased risk of basal ganglia dysfunction.

3,4-Dihydroxyphenylacetic Acid↗