Platelet-activating factor receptor activation. An initiator step in HIV-1 neuropathogenesis

Vir2Drug: a drug repurposing framework based on protein similarities between pathogens

We draw from the assumption that similarities between pathogens at both pathogen protein and host protein level, may provide the appropriate framework to identify and rank candidate drugs to be used against a specific pathogen. Vir2Drug is a drug repurposing tool that uses network-based approaches to identify and rank candidate drugs for a specific pathogen, combining information obtained from: (a) ranked pathogen-to-pathogen networks based on protein similarities between pathogens, (b) taxonomy distance between pathogens and (c) drugs targeting specific pathogen's and host proteins. The underlying pathogen networks are used to screen drugs by means of specific methodologies that account for either the host or pathogen's protein targets. Vir2Drug is a useful and yet informative tool for drug repurposing against known or unknown pathogens especially in periods where the emergence for repurposed drugs plays significant role in handling viral outbreaks, until reaching a vaccine. The web tool is available at: https://bioinformatics.cing.ac.cy/vir2drug, https://vir2drug.cing-big.hpcf.cyi.ac.cy.

Ceramide and Related Molecules in Viral Infections

Ceramide is a lipid messenger at the heart of sphingolipid metabolism. In concert with its metabolizing enzymes, particularly sphingomyelinases, it has key roles in regulating the physical properties of biological membranes, including the formation of membrane microdomains. Thus, ceramide and its related molecules have been attributed significant roles in nearly all steps of the viral life cycle: they may serve directly as receptors or co-receptors for viral entry, form microdomains that cluster entry receptors and/or enable them to adopt the required conformation or regulate their cell surface expression. Sphingolipids can regulate all forms of viral uptake, often through sphingomyelinase activation, and mediate endosomal escape and intracellular trafficking. Ceramide can be key for the formation of viral replication sites. Sphingomyelinases often mediate the release of new virions from infected cells. Moreover, sphingolipids can contribute to viral-induced apoptosis and morbidity in viral diseases, as well as virus immune evasion. Alpha-galactosylceramide, in particular, also plays a significant role in immune modulation in response to viral infections. This review will discuss the roles of ceramide and its related molecules in the different steps of the viral life cycle. We will also discuss how novel strategies could exploit these for therapeutic benefit.

Microglia Mediate HIV-1 gp120-Induced Synaptic Degeneration in Spinal Pain Neural Circuits

HIV-1 infection of the nervous system causes various neurological diseases, and synaptic degeneration is likely a critical step in the neuropathogenesis. Our prior studies revealed a significant decrease of synaptic protein, specifically in the spinal dorsal horn of patients with HIV-1 in whom pain developed, suggesting a potential contribution of synaptic degeneration to the pathogenesis of HIV-associated pain. However, the mechanism by which HIV-1 causes the spinal synaptic degeneration is unclear. Here, we identified a critical role of microglia in the synaptic degeneration. In primary cortical cultures (day in vitro 14) and spinal cords of 3- to 5-month-old mice (both sexes), microglial ablation inhibited gp120-induced synapse decrease. Fractalkine (FKN), a microglia activation chemokine specifically expressed in neurons, was upregulated by gp120, and knockout of the FKN receptor CX3CR1, which is predominantly expressed in microglia, protected synapses from gp120-induced toxicity. These results indicate that the neuron-to-microglia intercellular FKN/CX3CR1 signaling plays a role in gp120-induced synaptic degeneration. To elucidate the mechanism controlling this intercellular signaling, we tested the role of the Wnt/β-catenin pathway in regulating FKN expression. Inhibition of Wnt/β-catenin signaling blocked both gp120-induced FKN upregulation and synaptic degeneration, and gp120 stimulated Wnt/β-catenin-regulated FKN expression via NMDA receptors (NMDARs). Furthermore, NMDAR antagonist APV, Wnt/β-catenin signaling suppressor DKK1, or knockout of CX3CR1 alleviated gp120-induced mechanical allodynia in mice, suggesting a critical contribution of the Wnt/β-catenin/FKN/CX3R1 pathway to gp120-induced pain. These findings collectively suggest that HIV-1 gp120 induces synaptic degeneration in the spinal pain neural circuit by activating microglia via Wnt3a/β-catenin-regulated FKN expression in neurons.SIGNIFICANCE STATEMENT Synaptic degeneration develops in the spinal cord dorsal horn of HIV patients with chronic pain, but the patients without the pain disorder do not show this neuropathology, indicating a pathogenic contribution of the synaptic degeneration to the development of HIV-associated pain. However, the mechanism underlying the synaptic degeneration is unclear. We report here that HIV-1 gp120, a neurotoxic protein that is specifically associated with the manifestation of pain in HIV patients, induces synapse loss via microglia. Further studies elucidate that gp120 activates microglia by stimulating Wnt/β-catenin-regulated fractalkine in neuron. The results demonstrate a critical role of microglia in the pathogenesis of HIV-associated synaptic degeneration in the spinal pain neural circuit.

Association of TNF-α rs1799964 and IL-1β rs16944 polymorphisms with multiple system atrophy in Chinese Han population

BACKGROUND

Recent evidence suggested that several single nucleotide polymorphisms (SNPs) of inflammation-related genes (TNF-α rs1799964, IL-1α rs1800587, IL-1β rs16944, IL-8 rs4073, ICAM-1 rs5498) were associated with multiple system atrophy (MSA). Herein, we conducted this case-control study to evaluate the possible correlation between the five SNPs related to inflammation and MSA in Chinese Han population.

METHODS AND PATIENTS

We recruited 154 sporadic patients with MSA and 223 health controls in this study. All subjects were genotyped for the five SNPs using polymerase chain reaction amplification and Sanger sequencing.

RESULTS

TNF-α rs1799964, genotype distribution and minor allele frequency (MAF) showed significant differences between patients and controls, which might illustrate the minor allele C may increase the risk for MSA (genotype, P = 0.006, OR = 1.245, 95% CI = [1.066-1.455]; allele, P = 0.001, OR = 1.887, 95% CI = [1.303-2.733]). For rs16944, patients carrying AA genotype showed a nearly 5-year early age at onset (AAO) than GG genotype (50.52 ± 7.45 years vs. 54.90 ± 7.21 years, P = 0.037). No differences were found in genotype distribution and MAF of the five SNPs between patients with MSA with predominant cerebellar ataxia (MSA-C) and with predominant Parkinsonism (MSA-P).

CONCLUSION

Our study suggests that rs1799964 of TNF-α may act as a risk factor for MSA and the IL-1β rs16944 might be a genetic factor that modifies the AAO in MSA. Moreover, the exact mechanism of neuroinflammatory response in MSA deserves further exploration.

From peroxisomal disorders to common neurodegenerative diseases - the role of ether phospholipids in the nervous system

The emerging diverse roles of ether (phospho)lipids in nervous system development and function in health and disease are currently attracting growing interest. Plasmalogens, a subgroup of ether lipids, are important membrane components involved in vesicle fusion and membrane raft composition. They store polyunsaturated fatty acids and may serve as antioxidants. Ether lipid metabolites act as precursors for the formation of glycosyl-phosphatidyl-inositol anchors; others, like platelet-activating factor, are implicated in signaling functions. Consolidating the available information, we attempt to provide molecular explanations for the dramatic neurological phenotype in ether lipid-deficient human patients and mice by linking individual functional properties of ether lipids with pathological features. Furthermore, recent publications have identified altered ether lipid levels in the context of many acquired neurological disorders including Alzheimer's disease (AD) and autism. Finally, current efforts to restore ether lipids in peroxisomal disorders as well as AD are critically reviewed.

HIV-associated synaptic degeneration

Human immunodeficiency virus (HIV) infection induces neuronal injuries, with almost 50% of infected individuals developing HIV-associated neurocognitive disorders (HAND). Although highly activate antiretroviral therapy (HAART) has significantly reduced the incidence of severe dementia, the overall prevalence of HAND remains high. Synaptic degeneration is emerging as one of the most relevant neuropathologies associate with HAND. Previous studies have reported critical roles of viral proteins and inflammatory responses in this pathogenesis. Infected cells, including macrophages, microglia and astrocytes, may release viral proteins and other neurotoxins to stimulate neurons and cause excessive calcium influx, overproduction of free radicals and disruption of neurotransmitter hemostasis. The dysregulation of neural circuits likely leads to synaptic damage and loss. Identification of the specific mechanism of the synaptic degeneration may facilitate the development of effective therapeutic approaches to treat HAND.

Macrophages and Phospholipases at the Intersection between Inflammation and the Pathogenesis of HIV-1 Infection

Persistent low grade immune activation and chronic inflammation are nowadays considered main driving forces of the progressive immunologic failure in effective antiretroviral therapy treated HIV-1 infected individuals. Among the factors contributing to this phenomenon, microbial translocation has emerged as a key driver of persistent immune activation. Indeed, the rapid depletion of gastrointestinal CD4⁺ T lymphocytes occurring during the early phases of infection leads to a deterioration of the gut epithelium followed by the translocation of microbial products into the systemic circulation and the subsequent activation of innate immunity. In this context, monocytes/macrophages are increasingly recognized as an important source of inflammation, linked to HIV-1 disease progression and to non-AIDS complications, such as cardiovascular disease and neurocognitive decline, which are currently main challenges in treated patients. Lipid signaling plays a central role in modulating monocyte/macrophage activation, immune functions and inflammatory responses. Phospholipase-mediated phospholipid hydrolysis leads to the production of lipid mediators or second messengers that affect signal transduction, thus regulating a variety of physiologic and pathophysiologic processes. In this review, we discuss the contribution of phospholipases to monocyte/macrophage activation in the context of HIV-1 infection, focusing on their involvement in virus-associated chronic inflammation and co-morbidities.

Methylmercury induces the expression of TNF-α selectively in the brain of mice

Methylmercury selectively damages the central nervous system (CNS). The tumor necrosis factor (TNF) superfamily includes representative cytokines that participate in the inflammatory response as well as cell survival, and apoptosis. In this study, we found that administration of methylmercury selectively induced TNF-α expression in the brain of mice. Although the accumulated mercury concentration in the liver and kidneys was greater than in the brain, TNF-α expression was induced to a greater extent in brain. Thus, it is possible that there may exist a selective mechanism by which methylmercury induces TNF-α expression in the brain. We also found that TNF-α expression was induced by methylmercury in C17.2 cells (mouse neural stem cells) and NF-κB may participate as a transcription factor in that induction. Further, we showed that the addition of TNF-α antagonist (WP9QY) reduced the toxicity of methylmercury to C17.2 cells. In contrast, the addition of recombinant TNF-α to the culture medium decreased the cell viability. We suggest that TNF-α may play a part in the selective damage of the CNS by methylmercury. Furthermore, our results indicate that the higher TNF-α expression induced by methylmercury maybe the cause of cell death, as TNF-α binds to its receptor after being released extracellularly.

Current Understanding of Platelet-Activating Factor Signaling in Central Nervous System Diseases

Platelet-activating factor (PAF) is a bioactive lipid mediator which serves as a reciprocal messenger between the immune and nervous systems. PAF, a pluripotent inflammatory mediator, is extensively expressed in many cells and tissues and has either beneficial or detrimental effects on the progress of inflammation-related neuropathology. Its wide distribution and various biological functions initiate a cascade of physiological or pathophysiological responses during development or diseases. Current evidence indicates that excess PAF accumulation in CNS diseases exacerbates the inflammatory response and pathological consequences, while application of PAF inhibitors or PAFR antagonists by blocking this signaling pathway significantly reduces inflammation, protects cells, and improves the recovery of neural functions. In this review, we integrate the current findings of PAF signaling in CNS diseases and elucidate topics less appreciated but important on the role of PAF signaling in neurological diseases. We propose that the precise use of PAF inhibitors or PAFR antagonists that target the specific neural cells during the appropriate temporal window may constitute a potential therapy for CNS diseases.

Platelet-Activating Factor Receptors Mediate Excitatory Postsynaptic Hippocampal Injury in Experimental Autoimmune Encephalomyelitis

Gray matter degeneration contributes to progressive disability in multiple sclerosis (MS) and can occur out of proportion to measures of white matter disease. Although white matter pathology, including demyelination and axon injury, can lead to secondary gray matter changes, we hypothesized that neurons can undergo direct excitatory injury within the gray matter independent of these. We tested this using a model of experimental autoimmune encephalomyelitis (EAE) with hippocampal degeneration in C57BL/6 mice, in which immunofluorescent staining showed a 28% loss of PSD95-positive excitatory postsynaptic puncta in hippocampal area CA1 compared with sham-immunized controls, despite preservation of myelin and VGLUT1-positive excitatory axon terminals. Loss of postsynaptic structures was accompanied by appearance of PSD95-positive debris that colocalized with the processes of activated microglia at 25 d after immunization, and clearance of debris was followed by persistently reduced synaptic density at 55 d. In vitro, addition of activated BV2 microglial cells to hippocampal cultures increased neuronal vulnerability to excitotoxic dendritic damage following a burst of synaptic activity in a manner dependent on platelet-activating factor receptor (PAFR) signaling. In vivo treatment with PAFR antagonist BN52021 prevented PSD95-positive synapse loss in hippocampi of mice with EAE but did not affect development of EAE or local microglial activation. These results demonstrate that postsynaptic structures can be a primary target of injury within the gray matter in autoimmune neuroinflammatory disease, and suggest that this may occur via PAFR-mediated modulation of activity-dependent synaptic physiology downstream of microglial activation.

SIGNIFICANCE STATEMENT

Unraveling gray matter degeneration is critical for developing treatments for progressive disability and cognitive impairment in multiple sclerosis (MS). In a mouse model of MS, we show that neurons can undergo injury at their synaptic connections within the gray matter, independent of the white matter pathology, demyelination, and axon injury that have been the focus of most current and emerging treatments. Damage to excitatory synapses in the hippocampus occurs in association with activated microglia, which can promote excitotoxic injury via activation of receptors for platelet-activating factor, a proinflammatory signaling molecule elevated in the brain in MS. Platelet-activating factor receptor blockade protected synapses in the mouse model, identifying a potential target for neuroprotective treatments in MS.

Platelet-activating factor attenuation of long-term potentiation in rat hippocampal slices via protein tyrosine kinase signaling

It is well established that HIV-1-infected mononuclear phagocytes release platelet activating factor (PAF) and elevated levels of PAF have been detected in blood and in the cerebrospinal fluid (CSF) of acquired immunodeficiency syndrome (AIDS) patients with HIV-associated neurocognitive disorders (HAND). It is our hypothesis that the elevated levels of PAF alter long-term potentiation (LTP) in the hippocampus, leading to neurocognitive dysfunction. To test this hypothesis, we studied the effects of PAF on LTP in the CA1 region of rat hippocampal slices. Our results showed incubation of hippocampal slices with PAF attenuated LTP. The PAF-mediated attenuation was blocked by ginkgolide B, a PAF receptor antagonist, suggesting PAF attenuation of LTP via PAF receptors. Application of lyso-PAF, an inactive PAF analog, had no apparent effect on LTP. Further investigation revealed an involvement of tyrosine kinase in PAF attenuation of LTP, which was demonstrated by lavendustin A (a specific protein tyrosine kinase inhibitor) blockage of PAF attenuation of LTP. As LTP is widely considered as the cellular and synaptic basis for learning and memory, the attenuation of LTP by PAF may contribute at least in part to the HAND pathogenesis.

Platelet Activating Factor Enhances Synaptic Vesicle Exocytosis Via PKC, Elevated Intracellular Calcium, and Modulation of Synapsin 1 Dynamics and Phosphorylation

Platelet activating factor (PAF) is an inflammatory phospholipid signaling molecule implicated in synaptic plasticity, learning and memory and neurotoxicity during neuroinflammation. However, little is known about the intracellular mechanisms mediating PAF’s physiological or pathological effects on synaptic facilitation. We show here that PAF receptors are localized at the synapse. Using fluorescent reporters of presynaptic activity we show that a non-hydrolysable analog of PAF (cPAF) enhances synaptic vesicle release from individual presynaptic boutons by increasing the size or release of the readily releasable pool and the exocytosis rate of the total recycling pool. cPAF also activates previously silent boutons resulting in vesicle release from a larger number of terminals. The underlying mechanism involves elevated calcium within presynaptic boutons and protein kinase C activation. Furthermore, cPAF increases synapsin I phosphorylation at sites 1 and 3, and increases dispersion of synapsin I from the presynaptic compartment during stimulation, freeing synaptic vesicles for subsequent release. These findings provide a conceptual framework for how PAF, regardless of its cellular origin, can modulate synapses during normal and pathologic synaptic activity.

Cytoprotective Effects of Lysophospholipids from Sea Cucumber Holothuria atra

Lysophospholipids are important signaling molecules in animals and metazoan cells. They are widely distributed among marine invertebrates, where their physiological roles are unknown. Sea cucumbers produce unique lysophospholipids. In this study, two lysophospholipids were detected in Holothuria atra for the first time, lyso-platelet activating factor and lysophosphatidylcholine, with nuclear magnetic resonance and liquid chromatography-time-of-flight mass spectrometric analyses. The lipid fraction of H. atra contained lyso-platelet activating factor and lysophosphatidylcholine, and inhibited H2O2-induced apoptosis in the macrophage cell line J774A.1. The antioxidant activity of the lysophospholipid-containing lipid fraction of H. atra was confirmed with the oxygen radical absorbance capacity method. Our results suggest that the lysophospholipids from H. atra are potential therapeutic agents for the inflammation induced by oxidative stress.

In vivo effect of two first-line ART regimens on inflammatory mediators in male HIV patients

BACKGROUND

Persistent immune activation and inflammation are lying behind HIV-infection even in the setting of ART mediated viral suppression. The purpose of this study is to define the in vivo effect of two first-line ART regimens on certain inflammatory mediators in male HIV patients.

METHODS

Male, naive, HIV-infected volunteers were assigned either to tenofovir-DF/emtricitabine/efavirenz (Group_T) or abacavir/lamivudine/efavirenz (Group_A). Platelet Activating Factor (PAF) levels and metabolic enzymes together with HIV-implicated cytokines (IL-1beta, IL-6, IL-8, IL-10, IL-12p70, TNFa) and VEGF were determined for a 12-month period. Differences within each group were determined by non-parametric Friedman and Wilcoxon test, while the differences between the groups were checked by ANOVA repeated measures.

RESULTS

Both ART regimens present pronounced effect on inflammatory mediators, resulting in decreased PAF levels and Lipoprotein-associated phospholipase A2 (Lp-PLA2) activity for tenofovir-containing regimen and same as baseline PAF levels with a peak though at the 3rd month as well as elevated Lp-PLA2 activity for abacavir-containing regimen.

CONCLUSIONS

Studies regarding the effect of first-line ART regimens on inflammation may be beneficial in preventing chronic morbidities during HIV-treatment. From this point of view, the present study suggests an anti-inflammatory effect of tenofovir-containing ART, while the temporary increase of PAF levels in abacavir-containing ART may be the link between the reported cardiovascular risk and abacavir administration.

Intensive lifestyle modification reduces Lp-PLA2 in dyslipidemic HIV/HAART patients

PURPOSE

Patients with dyslipidemia associated with HIV-1 infection and highly active antiretroviral therapy (HAART) have elevated levels of Lp-PLA2 and CCL5/regulated on activation, normal T-cell expressed and secreted (RANTES), which may increase the risk of cardiovascular disease.

PURPOSE

This study aimed to determine whether an intensive diet and exercise (D/E) program, independently or combined with fenofibrate or niacin, could reduce Lp-PLA2 or RANTES.

METHODS

Patients with hypertriglyceridemic HIV on stable HAART (n = 107) were randomized to one of five interventions: 1) usual care, 2) D/E with placebos, 3) D/E with fenofibrate and placebo, 4) D/E with niacin and placebo, or 5) D/E with fenofibrate and niacin for 24 wk. Lp-PLA2 and RANTES concentrations were measured in fasting plasma samples at baseline and postintervention. General linear models were used to compare Lp-PLA2 and RANTES levels between the five groups postintervention, controlling for baseline levels, age, body mass index, CD4 T-cell count, viral load, duration of infection, and HAART.

RESULTS

At baseline, fasting plasma Lp-PLA2 (388.5 ± 127.5 ng·mL) and RANTES (43.8 ± 25.5 ng·mL) levels were elevated when compared with healthy controls. Posttreatment Lp-PLA2 mass was lower in patients who received D/E only (323.0 ± 27.2 ng·mL), D/E plus fenofibrate (327.2 ± 25.9 ng·mL), and D/E plus niacin (311.1 ± 27.8 ng·mL) when compared with patients receiving usual care (402.2 ± 25.3 ng·mL). RANTES concentrations were not significantly affected by any intervention.

CONCLUSIONS

Elevated plasma Lp-PLA2 mass can be reduced by an intensive D/E program in patients with HIV/HAART-associated dyslipidemia. RANTES is elevated but is not reduced by lifestyle modification, fenofibrate, or niacin.

Pharmacokinetic interactions of CEP-1347 and atazanavir in HIV-infected patients

CEP-1347 is a potent inhibitor of mixed lineage kinase (MLK), which was investigated for ameliorating HIV-associated neurocognitive disorders. CEP-1347 and atazanavir pharmacokinetics were determined when CEP-1347 50 mg twice daily was administered to HIV-infected patients (n = 20) receiving combination antiretroviral therapy including atazanavir and ritonavir (ATV/RTV, 300/100 mg) once daily continuously. Co-administration of CEP-1347 and ATV/RTV resulted with significant changes in pharmacokinetics of ATV but not RTV. Specifically, an increase in ATV accumulation ratio of 15 % (p = 0.007) and a prolongation of T(½) from 12.7 to 15.9 h (p = 0.002) were observed. The results suggested that co-administration of CEP-1347 with ATV/RTV in HIV-infected patients might result in limited impact on ATV but not on RTV pharmacokinetics.

Signalling or binding: the role of the platelet-activating factor receptor in invasive pneumococcal disease

Streptococcus pneumoniae (the pneumococcus) is an opportunistic human pathogen, which causes serious invasive disease such as pneumonia, bacteraemia and meningitis. The interaction of the bacteria with host receptors precedes the development of invasive disease. One host receptor implicated in pneumococcal adhesion to, invasion of and ultimately translocation of cell layers is the platelet-activating factor receptor (PAFR). PAFR is a G-protein coupled receptor which binds PAF, a potent phospholipid activator involved in many leucocyte functions, platelet aggregation and inflammation. PAFR has been proposed to bind S. pneumoniae and as such facilitate adhesion to, uptake by and transcytosis of endothelial cells leading to invasive disease. However, there is a shortage of biochemical data supporting direct interaction between PAFR and the bacteria, in addition to conflicting data on its role in development of invasive pneumococcal disease (IPD). In this review, we will discuss current literature on PAFR and S. pneumoniae and other pathogens,including data concerning human PAFR genetic variation related to IPD clinical aspects, to shed light on the importance of PAFR in IPD. Clarification of the role of this receptor in IPD development has the potential to enable the development of novel therapeutic strategies for treating pneumococcal disease by interfering with the PAFR.

Advances in brain targeting and drug delivery of anti-HIV therapeutic agents

INTRODUCTION

Human immunodeficiency virus (HIV) is a neurotropic virus that enters the central nervous system (CNS) early in the course of infection. Although antiretroviral drugs are able to eliminate the majority of the HIV virus in the bloodstream, however, no specific treatment currently exist for CNS infections related to HIV. This is mainly attributed to the poor penetrability of antiretroviral therapy across the blood-brain barrier (BBB), and the protective nature of the BBB. Therefore, in order to increase the efficacy of anti-HIV drugs, novel drug delivery methodologies that can exhibit activity in the CNS are most needed and warranted.

AREAS COVERED

In this review article, the authors discussed the challenges with delivering drugs to the brain especially under HIV infection pathophysiology status. Also, they discussed the approaches currently being investigated to enhance brain targeting of anti-HIV drugs. A literature search was performed to cover advances in major approaches used to enhance drug delivery to the brain.

EXPERT OPINION

If drugs could reach the CNS in sufficient quantity by the methodologies discussed, mainly through intranasal administration and the utilization of nanotechnology, this could generate interest in previously abandoned therapeutic agents and enable an entirely novel approach to CNS drug delivery.

Effects of HAART on platelet-activating factor metabolism in naive HIV-infected patients I: study of the tenofovir-DF/emtricitabine/efavirenz HAART regimen

Platelet-activating factor (PAF) is implicated in human immunodeficiency virus (HIV)-related manifestations. Increased PAF synthesis has been recently detected in HIV-infected patients. In this study, we examined in naive HIV-infected patients the in vivo effects of a highly active antiretroviral therapy (HAART) regimen, containing tenofovir-DF/emtricitabine/efavirenz, on PAF metabolism. The specific activities of PAF basic biosynthetic enzymes, PAF-cholinephosphotransferase (PAF-CPT) and lyso-PAF-acetyltransferase (lyso-PAF-AT), but also the ones of PAF-basic catabolic enzymes, PAF acetylhydrolase (PAF-AH) in leukocytes and platelets, and lipoprotein-associated-phospholipase-A(2) (LpPLA(2)) in plasma, were measured in blood samples of eight asymptomatic naive male HIV-infected patients just before and after 1, 3, and 6 months of treatment. CD4 cell counts, viral load, and several biochemical markers were also measured in the same blood samples of these patients. The repeated measures ANOVA and the Pearson r criterion were used to study statistical differences and correlations-partial correlations, while linear mixed models were conducted in order to estimate association(s) between time-dependent changes in these factors. Before treatment, the activities of PAF-CPT in leukocytes and LpPLA(2) in plasma were found to be inversely correlated with CD4 cell counts and positively correlated with the viral load. After 6 months of treatment, the activities of basic PAF-biosynthetic enzymes, PAF-CPT and lyso-PAF-AT, were both reduced in leukocytes. At 6 months, PAF-AH activity was also reduced in these cells, while LpPLA(2) remained stable. The reduction of PAF-CPT occurred even from the first month, while there is a time-dependent correlation between the increase of CD4 and the decrease of both viral load and PAF-CPT of leukocytes during treatment. Apart from its classical antiretroviral activities the tenofovir-DF/emtricitabine/efavirenz regimen also exhibited favorable effects on PAF metabolism and therefore may also display beneficial effects in some HIV-related conditions, such as cardiovascular disease (CVD), in which PAF is implicated.

Effects of highly active antiretroviral therapy on platelet activating factor metabolism in naive HIV-infected patients: ii) study of the abacavir/lamivudine/efavirenz HAART regimen

Human Immunodeficiency Virus (HIV)-infected patients are at increased risk for cardiovascular diseases partly due to chronic inflammation. Some antiretroviral drugs and Highly Active Anti-Retroviral Therapy (HAART) regimens seem to be related and amplify this increased risk, especially the ones containing abacavir. Platelet-Activating-Factor (PAF) is a potent inflammatory mediator that is implicated in both cardiovascular diseases and HIV-related manifestations. Our objective is to study the in vivo effect of the abacavir/lamivudine/efavirenz first-line HAART regimen on PAF metabolism in HIV-infected patients. The specific activities of PAF basic biosynthetic enzymes in leukocytes and platelets, PAF-cholinephosphotransferase (PAF-CPT) and lyso-PAF-acetyltransferase (Lyso-PAF-AT), but also those of PAF-basic catabolic enzymes, PAF acetylhydrolase (PAF-AH) in leukocytes and platelets and Lipoprotein-associated-Phospholipase-A2 (LpPLA2) in plasma, were measured in blood samples of 10 asymptomatic naïve male HIV-infected patients just before and after 1, 3 and 6 months of treatment. CD4 cell counts, viral load and several biochemical markers were also measured in the same blood samples of these patients. The repeated ANOVA measures and the Pearson r criterion were used for studying statistical differences and correlations - partial correlations respectively. Even though viral load was decreased and CD4 cell counts were beneficially increased after treatment with the abacavir/lamivudine/efavirenz regimen, the main enzyme of the remodelling PAF-synthesis that is implicated in pro-atherogenic inflammatory procedures, Lyso-PAF-AT activity, was increased at 3 months of treatment in both leukocytes and platelets, while the main enzyme of PAF-degradation, PAF-AH, was increased as a response only in leukocytes at the 3rd month. Although the abacavir/lamivudine/efavirenz HAART regimen exhibits very efficient antiretroviral activities, on the other hand it induces an in vivo transient increase in the inflammation-related remodeling PAF-biosynthetic pathway. This finding supports the hypothesis of inflammation-mediated increased cardiovascular risk in HIV-infected patients during the first months of abacavir-containing HAART.

HIV-1 Tat-induced microgliosis and synaptic damage via interactions between peripheral and central myeloid cells

Despite the ability of combination antiretroviral treatment (cART) to reduce viral burden to nearly undetectable levels in cerebrospinal fluid and serum, HIV-1 associated neurocognitive disorders (HAND) continue to persist in as many as half the patients living with this disease. There is growing consensus that the actual substrate for HAND is destruction of normal synaptic architecture but the sequence of cellular events that leads to this outcome has never been resolved. To address whether central vs. peripheral myeloid lineage cells contribute to synaptic damage during acute neuroinflammation we injected a single dose of the HIV-1 transactivator of transcription protein (Tat) or control vehicle into hippocampus of wild-type or chimeric C57Bl/6 mice genetically marked to distinguish infiltrating and resident immune cells. Between 8–24 hr after injection of Tat, invading CD11b⁺ and/or myeloperoxidase-positive leukocytes with granulocyte characteristics were found to engulf both microglia and synaptic structures, and microglia reciprocally engulfed invading leukocytes. By 24 hr, microglial processes were also seen ensheathing dendrites, followed by inclusion of synaptic elements in microglia 7 d after Tat injection, with a durable microgliosis lasting at least 28 d. Thus, central nervous system (CNS) exposure to Tat induces early activation of peripheral myeloid lineage cells with phagocytosis of synaptic elements and reciprocal microglial engulfment of peripheral leukocytes, and enduring microgliosis. Our data suggest that a single exposure to a foreign antigen such as HIV-1 Tat can lead to long-lasting disruption of normal neuroimmune homeostasis with deleterious consequences for synaptic architecture, and further suggest a possible mechanism for enduring neuroinflammation in the absence of productive viral replication in the CNS.

In Vivo Effects of a Ginkgo Biloba Extract on Platelet Activating Factor Metabolism in Two Asymptomatic Hiv-Infected Patients

Ginkgo biloba products seem to protect from several pathological conditions, including HIV manifestations, where Platelet Activating Factor (PAF) is implicated. In the present study, we examined for the first time the in vivo effects of a standardized formulation of Ginkgo biloba extract (150 mg daily, per os) on PAF metabolism in blood cells and plasma of two male, asymptomatic HIV-infected patients, not receiving antiretroviral treatment, during a 9-month period. These patients differed at baseline in terms of duration of HIV infection, viral load levels, CD4 cell counts and Highly Active Antiretroviral Therapy (HAART) experience. In the first patient with early HIV infection, after an initial transient increase, a return of both plasma viral load and PAF biosynthetic enzyme activities in leukocytes to their baseline levels was observed during Ginkgo biloba use. As a result PAF degradation also remained low in this patient. The second patient with late but not advanced HIV infection, had higher levels of viral load and a lower CD4 cell count at baseline. The use of 150 mg of a Ginkgo biloba extract was probably insufficient to induce PAF degradation and/or to suppress the induction of PAF biosynthesis observed. At the same time, the initial high levels of viral load were further increased and CD4 cell counts were finally decreased during the study. The observed differences in PAF metabolism during Ginkgo use seem to be related to the initial heterogeneity of these patients. It appears that in some HIV-infected patients inhibition of the PAF/PAF-receptor system, along with a decrease/down-regulation of PAF-biosynthesis, illustrates a new potential role for Ginkgo biloba compounds in the treatment of HIV infection and its manifestations. However, more tests on a larger number of patients are needed in order to support these preliminary observations.

Antiplatelet activity of valproic acid contributes to decreased soluble CD40 ligand production in HIV type 1-infected individuals

CD40L is a type II membrane glycoprotein of the TNF family that is found on activated T cells, B cells, and platelets. We previously reported that the soluble form of this inflammatory mediator (sCD40L) is elevated in the plasma and cerebrospinal fluid of HIV-1-infected, cognitively impaired individuals. In this study, we demonstrate that the mood-stabilizing drug valproic acid (VPA) reduces sCD40L levels in plasma samples of HIV-1-infected patients (n = 23) and in washed human platelets, which are the main source of circulating sCD40L. VPA also inhibited HIV-1 transactivator of transcription-induced release of sCD40L and platelet factor 4 in C57BL/6 mice. The mechanism by which VPA was able to do so was investigated, and we demonstrate that VPA, a known glycogen synthase kinase 3β inhibitor, blocks platelet activating factor-induced activation of glycogen synthase kinase 3β in platelets in a manner that alters sCD40L release from platelets. These data reveal that VPA has antiplatelet activity, and they convey important implications for the potential of VPA as an adjunct therapy not only for cognitively impaired patients with HIV-1 infection, but also numerous inflammatory diseases for which such antiplatelet therapies are currently lacking.

Nuclear factor-kappa B family member RelB inhibits human immunodeficiency virus-1 Tat-induced tumor necrosis factor-alpha production

Human Immunodeficiency Virus-1 (HIV-1)-associated neurocognitive disorder (HAND) is likely neuroinflammatory in origin, believed to be triggered by inflammatory and oxidative stress responses to cytokines and HIV protein gene products such as the HIV transactivator of transcription (Tat). Here we demonstrate increased messenger RNA for nuclear factor-kappa B (NF-κB) family member, transcription factor RelB, in the brain of doxycycline-induced Tat transgenic mice, and increased RelB synthesis in Tat-exposed microglial cells. Since genetic ablation of RelB in mice leads to multi-organ inflammation, we hypothesized that Tat-induced, newly synthesized RelB inhibits cytokine production by microglial cells, possibly through the formation of transcriptionally inactive RelB/RelA complexes. Indeed, tumor necrosis factor-alpha (TNFα) production in monocytes isolated from RelB deficient mice was significantly higher than in monocytes isolated from RelB expressing controls. Moreover, RelB overexpression in microglial cells inhibited Tat-induced TNFα synthesis in a manner that involved transcriptional repression of the TNFα promoter, and increased phosphorylation of RelA at serine 276, a prerequisite for increased RelB/RelA protein interactions. The Rel-homology-domain within RelB was necessary for this interaction. Overexpression of RelA itself, in turn, significantly increased TNFα promoter activity, an effect that was completely blocked by RelB overexpression. We conclude that RelB regulates TNFα cytokine synthesis by competitive interference binding with RelA, which leads to downregulation of TNFα production. Moreover, because Tat activates both RelB and TNFα in microglia, and because Tat induces inflammatory TNFα synthesis via NF-κB, we posit that RelB serves as a cryoprotective, anti-inflammatory, counter-regulatory mechanism for pathogenic NF-κB activation. These findings identify a novel regulatory pathway for controlling HIV-induced microglial activation and cytokine production that may have important therapeutic implications for the management of HAND.

Lithium therapy for human immunodeficiency virus type 1-associated neurocognitive impairment

The objective of this study was to assess lithium safety and tolerability and to explore its impact on cognition, function, and neuroimaging biomarkers in human immunodeficiency virus (HIV)-infected subjects with cognitive impairment. Fifteen cognitively impaired HIV-infected subjects were enrolled in this 10-week open-label study of lithium 300 mg twice daily. Neuroimaging was performed at baseline and following 10 weeks of treatment and included magnetic resonance spectroscopy (MRS), diffusion tensor imaging (DTI), and functional MRI (fMRI). Thirteen of the 14 subjects (93%) that complied with the study visits were able to complete the study on lithium and 11 out of 13 (79%) completed the study at the originally assigned dose of 300 mg twice daily. There were no significant changes in CD4(+) lymphocyte cell count and plasma HIV RNA. Cognitive performance and depressive mood did not improve significantly after the 10-week lithium treatment; however, neuroimaging revealed a decrease in the glutamate+glutamine (Glx) peak in the frontal gray matter, increased fractional anisotropy, and decreased mean diffusivity in several brain areas, and changes in brain activation patterns, suggestive of improvement. These results suggest that lithium can be used safely in HIV-infected individuals with cognitive impairment. Furthermore, the neuroimaging results suggest that lithium may improve HIV-associated central nervous system (CNS) injury; thus, further investigations of lithium as an adjunctive treatment for HIV-associated cognitive impairment are warranted.

Development of a platelet-activating factor antagonist for HIV-1 associated neurocognitive disorders

The neuroregulatory activities of PMS-601, a platelet activating factor antagonist, were investigated in laboratory and animal models of HIV-1 encephalitis (HIVE). For the former, PMS-601 reduced monocyte-derived macrophage pro-inflammatory secretions, multinucleated giant cell (MGC) formation, and neuronal loss independent of antiretroviral responses. PMS-601 treatment of HIVE severe combined immunodeficient mice showed reduced microgliosis, MGCs and neurodegeneration. These observations support the further development of PMS-601 as an adjunctive therapy for HIV-1 associated neurocognitive disorders.

The role of alcohol on platelets, thymus and cognitive performance among HIV-infected subjects: are they related?

Our objective was to evaluate whether thrombocytopenia and small thymus volume, which may be associated with hazardous alcohol consumption, are predictors of cognitive performance after highly-active antiretroviral treatment (HAART). To achieve this goal 165 people living with HIV starting HAART underwent thymus magnetic resonance imaging, cognitive (HIV Dementia Score [HDS] and the California Verbal Learning Test [CVLT]), immune and laboratory assessments at baseline and after 6 months of HAART. At baseline, hazardous alcohol consumption was significantly correlated with both thymus size (r = -0.44, p = 0.003) and thrombocytopenia (r = 0.28, p = 0.001). Of interest, thrombocytopenic patients were characterized by a smaller thymus size. Individuals with and without cognitive impairment differed in alcohol consumption, platelet counts and thymus size, suggesting that they may be risk factors for neurological abnormalities. In fact, after HAART hazardous alcohol use associations with thrombocytopenia were related to cognitive decline (learning = -0.2 +/- 0.8, recall = -0.3 +/- 0.1 and HDS = -0.5). This contrasted with improvements on every cognitive measure (learning = 1.6 +/- 0.3, p = 0.0001, recall = 2.2 +/- 0.4, p = 0.0001 and HDS = 1.0, p = 0.05) in those with neither alcohol use nor thrombocytopenia. In adjusted analyses for sociodemographics, adherence and immune measurements, reduced thymus size was associated with a 90% and thrombocytopenia with a 70% increase in the risk of scoring in the demented range after HAART (RR = 1.9, p < 0.05 and RR = 1.7, p = 0.03) and with low CVLT scores (thymus volume RR = 2.0, p = 0.04, chronic alcohol use p = 0.05 and thrombocytopenia p = 0.06). Thymus volume and platelet counts were negatively affected by alcohol and were predictors of cognitive performance and improvements after HAART. These results could have important clinical and therapeutic implications.

Protection of PMS777, a new AChE inhibitor with PAF antagonism, against amyloid-beta-induced neuronal apoptosis and neuroinflammation

Amyloid-beta (Abeta) plays a central role in the neuroinflammation and cholinergic neuronal apoptosis in Alzheimer's disease, and thus has been considered as a main determinant of this disease. In the previous study, we reported that PMS777, a novel bis-interacting ligand for acetylcholinesterase (AChE) inhibition and platelet-activating factor (PAF) receptor antagonism, could significantly attenuate PAF-induced neurotoxicity. Continuing our efforts, we further investigated the protective effect of PMS777 on Abeta-induced neuronal apoptosis in vitro and neuroinflammation in vivo. PMS777 (1-100 microM) was found to inhibit Abeta-induced human neuroblastoma SH-SY5Y cell apoptosis in a concentration-dependent manner. Concurrently, PMS777 increased ratio of bcl-2 to bax mRNA, and inhibited both mRNA expression and activity of caspase-3 in SH-SY5Y cells after the exposure with Abeta. In vivo experimental study demonstrated that PMS777 could attenuate Abeta-induced microglial and astrocytic activation in the rat hippocampus after systemic administration. These results suggest that PMS777 potently protects against Abeta-induced neuronal apoptosis and neuroinflammation, and warrants further investigations in connection with its potential value in the treatment of Alzheimer's disease.

Ceramide and neurodegeneration: susceptibility of neurons and oligodendrocytes to cell damage and death

Neurodegenerative disorders are marked by extensive neuronal apoptosis and gliosis. Although several apoptosis-inducing agents have been described, understanding of the regulatory mechanisms underlying modes of cell death is incomplete. A major breakthrough in delineation of the mechanism of cell death came from elucidation of the sphingomyelin (SM)-ceramide pathway that has received worldwide attention in recent years. The SM pathway induces apoptosis, differentiation, proliferation, and growth arrest depending upon cell and receptor types, and on downstream targets. Sphingomyelin, a plasma membrane constituent, is abundant in mammalian nervous system, and ceramide, its primary catabolic product released by activation of either neutral or acidic sphingomyelinase, serves as a potential lipid second messenger or mediator molecule modulating diverse cellular signaling pathways. Neutral sphingomyelinase (NSMase) is a key enzyme in the regulated activation of the SM cycle and is particularly sensitive to oxidative stress. In a context of increasing clarification of the mechanisms of neurodegeneration, we thought that it would be useful to review details of recent findings that we and others have made concerning different pro-apoptotic neurotoxins including proinflammatory cytokines, hypoxia-induced SM hydrolysis and ceramide production that induce cell death in human primary neurons and primary oligodendrocytes: redox sensitive events. What has and is emerging is a vista of therapeutically important ceramide regulation affecting a variety of different neurodegenerative and neuroinflammatory disorders.

HIV-1 Tat activates neuronal ryanodine receptors with rapid induction of the unfolded protein response and mitochondrial hyperpolarization

Neurologic disease caused by human immunodeficiency virus type 1 (HIV-1) is ultimately refractory to highly active antiretroviral therapy (HAART) because of failure of complete virus eradication in the central nervous system (CNS), and disruption of normal neural signaling events by virally induced chronic neuroinflammation. We have previously reported that HIV-1 Tat can induce mitochondrial hyperpolarization in cortical neurons, thus compromising the ability of the neuron to buffer calcium and sustain energy production for normal synaptic communication. In this report, we demonstrate that Tat induces rapid loss of ER calcium mediated by the ryanodine receptor (RyR), followed by the unfolded protein response (UPR) and pathologic dilatation of the ER in cortical neurons in vitro. RyR antagonism attenuated both Tat-mediated mitochondrial hyperpolarization and UPR induction. Delivery of Tat to murine CNS in vivo also leads to long-lasting pathologic ER dilatation and mitochondrial morphologic abnormalities. Finally, we performed ultrastructural studies that demonstrated mitochondria with abnormal morphology and dilated endoplasmic reticulum (ER) in brain tissue of patients with HIV-1 inflammation and neurodegeneration. Collectively, these data suggest that abnormal RyR signaling mediates the neuronal UPR with failure of mitochondrial energy metabolism, and is a critical locus for the neuropathogenesis of HIV-1 in the CNS.

Anti-platelet-activating factor effects of highly active antiretroviral therapy (HAART): a new insight in the drug therapy of HIV infection?

Platelet-activating factor (PAF) is a potent inflammatory mediator, which seems to play a role in the pathogenesis of several AIDS manifestations such as AIDS dementia complex, Kaposi's sarcoma, and HIV-related nephropathy. PAF antagonists have been studied in these conditions with promising results. In order to examine the possible interactions between PAF and antiretroviral therapy, we studied the effect of nucleoside reverse transcriptase inhibitors, non-nucleoside reverse transcriptase inhibitors, and protease inhibitors against PAF biological activities and its basic biosynthetic enzymes dithiothreitol-insensitive PAF-cholinephosphotransferase (PAF-CPT) and lyso-PAF-acetyltransferase (Lyso-PAF-AT), as well as its main degradative enzyme PAF-acetylhydrolase, of human mesangial cell line (HMC). We also studied the effect of several backbones and highly active antiretroviral therapy (HAART) regimens against PAF activity. Among the drugs tested, several inhibited PAF-induced platelet aggregation in a concentration-depended manner, with tenofovir, efavirenz, and ritonavir exhibiting the higher inhibitory effect. In addition, when these drugs were combined in backbones and HAART regimens based on American antiretroviral therapy proposals, they also synergistically exhibited an inhibitory effect against PAF-induced platelet aggregation. Several of these drugs have also inhibited in vitro microsomal PAF-CPT activity, and concentrations of lopinavir-r or tenofovir-DF (similar to their IC(50) against PAF-induced platelet aggregation) exhibited the same effect against PAF-CPT and Lyso-PAF-AT when added in the cell medium of cultured HMC. In addition, in naïve patients treated with one of the most potent anti-PAF HAART regimens (efavirenz/emtricitabine/tenofovir-DF) for a period of 1 month, a significant reduction of the specific activity of PAF-CPT of washed human leukocytes of these patients was also observed, compared with its levels before the HAART treatment. These promising results need to be further studied and confirmed by additional in vivo tests in order to optimize HAART efficacy.

Polyunsaturated fatty acids block platelet-activating factor-induced phosphatidylinositol 3 kinase/Akt-mediated apoptosis in intestinal epithelial cells

We have shown earlier that platelet-activating factor (PAF) causes apoptosis in enterocytes via a mechanism that involves Bax translocation to mitochondria, followed by caspase activation and DNA fragmentation. Herein we report that, in rat small intestinal epithelial cells (IEC-6), these downstream apoptotic effects are mediated by a PAF-induced inhibition of the phosphatidylinositol 3-kinase (PI 3-kinase)/protein kinase B (Akt) signaling pathway. Treatment with PAF results in rapid dephosphorylation of Akt, phosphoinositide-dependent kinase-1, and the YXXM p85 binding motif of several proteins and redistribution of Akt-pleckstrin homology domain-green fluorescent protein, i.e., an in vivo phosphatidylinositol (3,4,5)-trisphosphate sensor, from membrane to cytosol. The proapoptotic effects of PAF were inhibited by both n-3 and n-6 polyunsaturated fatty acids but not by a saturated fatty acid palmitate. Indomethacin, an inhibitor of prostaglandin biosynthesis, did not influence the baseline or PAF-induced apoptosis, but 2-bromopalmitate, an inhibitor of protein palmitoylation, inhibited all of the proapoptotic effects of PAF. Our data strongly suggest that an inhibition of the PI 3-kinase/Akt signaling pathway is the main mechanism of PAF-induced apoptosis in enterocytes and that polyunsaturated fatty acids block this mechanism very early in the signaling cascade independently of any effect on prostaglandin synthesis, and probably directly via an effect on protein palmitoylation.

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.

Protection against human immunodeficiency virus type 1 Tat neurotoxicity by Ginkgo biloba extract EGb 761 involving glial fibrillary acidic protein

Human immunodeficiency virus (HIV)-1 Tat protein is an important pathogenic factor in HIV-associated neuropathogenesis. Despite recent progress, the molecular mechanisms underlying Tat neurotoxicity are still not completely understood. However, few therapeutics have been developed to specifically target HIV infection in the brain. Recent development of an inducible brain-specific Tat transgenic mouse model has made it possible to define the mechanisms of Tat neurotoxicity and evaluate anti-neuroAIDS therapeutic candidates in the context of a whole organism. Herein, we demonstrate that administration of EGb 761, a standardized formulation of Ginkgo biloba extract, markedly protected Tat transgenic mice from Tat-induced developmental retardation, inflammation, death, astrocytosis, and neuron loss. EGb 761 directly down-regulated glial fibrillary acidic protein (GFAP) expression at both protein and mRNA levels. This down-regulation was, at least in part, attributable to direct effects of EGb 761 on the interactions of the AP1 and NF-kappaB transcription factors with the GFAP promoter. Most strikingly, Tat-induced neuropathological phenotypes including macrophage/microglia activation, central nervous system infiltration of T lymphocytes, and oxidative stress were significantly alleviated in GFAP-null/Tat transgenic mice. Taken together, these results provide the first evidence to support the potential for clinical use of EGb 761 to treat HIV-associated neurological diseases. Moreover, these findings suggest for the first time that GFAP activation is directly involved in Tat neurotoxicity, supporting the notion that astrocyte activation or astrocytosis may directly contribute to HIV-associated neurological disorders.

Platelet activating factor-induced neuronal apoptosis is initiated independently of its G-protein coupled PAF receptor and is inhibited by the benzoate orsellinic acid

The bioactive lipid mediator platelet activating factor (PAF) is recognized as a key effecter of neuronal apoptosis, yet it is not clear whether its G-protein coupled receptor (PAFR) initiates or prevents PAF neurotoxicity. Using PAFR-/- and congenic wild-type mice, we show that PAF triggers caspase-3/7 activity and neuronal death in PAFR-/- but not PAFR+/+ cerebellar granule neurons. Restoring receptor expression by recombinant adenoviral infection protected cells from PAF challenge. Neuronal death was not mediated by nitric oxide or N-methyl-d-aspartate receptor signaling given that N-nitro-l-arginine methyl ester and MK-801 did not inhibit PAF-induced neuronal loss in PAFR-/- neurons. To intervene in PAFR-independent neurotoxicity, the anti-apoptotic actions of three structurally distinct PAF antagonists were compared to a panel of plant and fungal benzoic acid derivatives. We found that the PAF antagonist BN 52021 but not FR 49175 or CV 3988 inhibited PAFR-independent neurotoxicity. Orsellinic acid, a fungal-derived benzoic acid, blocked PAF-mediated neuronal apoptosis without affecting PAFR-mediated neuroprotection. These findings demonstrate that PAF can transduce apoptotic death in primary neurons independently of its G-protein coupled receptor, that PAFR activation is neuroprotective, and that orsellinic acid effectively attenuates PAFR-independent neuronal apoptosis.

PMS777, A Bis-interacting Ligand for PAF Receptor Antagonism and AChE Inhibition, Attenuates PAF-induced Neurocytotoxicity in SH-SY5Y Cells

(1) HIV-1 and viral proteins-evoked chronic brain inflammation, which is characterized by microglial activation, is the pivotal neuropathogenesis of HIV-1-associated dementia (HAD). Platelet-activating factor (PAF), mainly released from activated microglia and acts as a high potent inflammatory mediator and a neurotoxin, is indicated to be a principle initiator of neuroinflammation, neuronal dysfunction, and apoptosis related to HAD. Thus, bis-interacting ligands of acetylcholinesterase (AChE) inhibition and PAF receptor antagonism would be of great interest in the therapeutic potential of HAD not only for improvement of cognitive performance, but also for disease-modifying. (2). We have previously reported that a novel tetrahydrofuran-derived bis-interacting ligand PMS777 had satisfying potencies for PAF receptor blockade and AChE inhibition, and markedly improved cholinergic dysfunction-induced cognitive impairment in mice. Continuing with our research, we further investigated the neuroprotective activities of PMS777 on PAF-triggered neuronal injury in human neuroblastoma SH-SY5Y cells. (3) The bis-interacting ligand PMS777 (10 muM) obviously alleviated PAF-induced cell apoptosis in SH-SY5Y cells. Pretreatment with PMS777 also markedly inhibited intracellular Ca(2+) overload, down-regulation of anti-apoptotic bcl-2 mRNA, stimulation of pro-apoptotic bax mRNA expression and activation of caspase-3 pathway. Also, PMS777 could fine-tune pro-inflammatory cyclooxygenase-2 (cox-2) mRNA expression in PAF-treated cells. (4) These results suggest that PMS777 possesses a neuroprotective profile via anti-apoptotic/inflammatory signaling and warrant further investigations in connection with the potential value of this compound in HAD treatment.

The phospholipid mediator platelet-activating factor mediates striatal synaptic facilitation

The phospholipid mediator platelet-activating factor (PAF), an endogenous modulator of glutamatergic neurotransmission, can also be secreted by brain mononuclear phagocytes during HIV-1 infection. Platelet-activating factor can induce neuronal apoptosis by NMDA receptor-dependent and independent mechanisms. We now demonstrate that acute administration of sublethal doses of PAF to striatal slices augments synaptic facilitation in striatal neurons following high-frequency stimulation, which can be blocked by PAF receptor antagonists, suggesting that striatal synaptic facilitation can be augmented by PAF receptor agonism. We also demonstrate that repeated sublethal doses of PAF during tetanic stimulation can greatly increase the magnitude of postsynaptic potentials and action potentials, but a lethal dose of PAF destroys the capacity of corticostriatal synapses to achieve this augmented synaptic facilitation. Thus, the relative concentration and temporal pattern of PAF expression at glutamatergic synapses may govern whether it acts in a physiologic or pathophysiologic manner during striatal neurotransmission.

HIV-1 trans activator of transcription protein elicits mitochondrial hyperpolarization and respiratory deficit, with dysregulation of complex IV and nicotinamide adenine dinucleotide homeostasis in cortical neurons

HIV-1 causes a common, progressive neurological disorder known as HIV-associated dementia (HAD). The prevalence of this disorder has increased despite the use of highly active antiretroviral therapy, and its underlying pathogenesis remains poorly understood. However, evidence suggests that some aspects of HAD may be reversible. To model the reversible aspects of HAD, we have used the HIV-1 neurotoxin trans activator of transcription protein (Tat) to investigate nonlethal changes in cultured neurons. Exposure of rodent cortical neurons to sublethal concentrations of Tat elicits mitochondrial hyperpolarization. In this study, we used the cationic lipophilic dye rhodamine 123 to confirm this observation, and then performed follow-up studies to examine the mechanism involved. In intact neurons, we found Tat elicited a rapid drop in internal mitochondrial pH, and addition of Tat to purified mitochondrial extracts inhibited complex IV of the electron transport chain. To correlate enzyme activity in mitochondrial extracts with results in intact cells, we measured neuronal respiration following Tat exposure. Cortical neurons demonstrated decreased respiration upon Tat treatment, consistent with inhibition of complex IV. We examined mitochondrial Ca(2+) homeostasis using a mitochondrial targeted enhanced yellow fluorescent protein-calmodulin construct. We detected a decrease in mitochondrial calcium concentration following exposure to Tat. Finally, we measured the energy intermediate NAD(P)H after Tat treatment, and found a 20% decrease in the autofluorescence. Based on these findings, we suggest that decreased NADPH and calcium concentration contribute to subsequent respiratory decline after exposure to Tat, with detrimental effects on neuronal signaling.

Functional Synergy between CD40 Ligand and HIV-1 Tat Contributes to Inflammation: Implications in HIV Type 1 Dementia

HIV type 1 (HIV-1)-associated dementia (HAD) is believed to occur due to aberrant activation of monocyte-derived macrophages and brain-resident microglial cells by viral proteins as well as by the proinflammatory mediators released by infected cells. To investigate the inflammatory aspects of the disease, we examined the levels of soluble CD40L (sCD40L) in paired samples of plasma and cerebrospinal fluid obtained from 25 HIV-infected individuals. A significantly higher level of sCD40L was detected in both cerebrospinal fluid and plasma from HIV-infected patients with cognitive impairment, compared with their nonimpaired counterparts. The contribution of sCD40L to the pathogenesis of HAD was then examined by in vitro experiments. rCD40L synergized with HIV-1 Tat to increase TNF-alpha release from primary human monocytes and microglia, in an NF-kappaB-dependent manner. The mechanistic basis for this synergism was attributed to a Tat-mediated up-regulation of CD40 in monocytes and microglia. Finally, the CD40L-mediated increase in TNF-alpha production by monocytes was shown to be biologically important; immunodepletion experiments revealed that TNF-alpha was essential for the neurotoxic effects of conditioned medium recovered from Tat/CD40L-treated monocytes. Taken together, our results show that CD40 signaling in microglia and monocytes can synergize with the effects of Tat, further amplifying inflammatory processes within the CNS and influencing neuronal survival.

Cholesterol synthesis inhibitors protect against platelet-activating factor-induced neuronal damage

BACKGROUND

Platelet-activating factor (PAF) is implicated in the neuronal damage that accompanies ischemia, prion disease and Alzheimer's disease (AD). Since some epidemiological studies demonstrate that statins, drugs that reduce cholesterol synthesis, have a beneficial effect on mild AD, we examined the effects of two cholesterol synthesis inhibitors on neuronal responses to PAF.

METHODS

Primary cortical neurons were treated with cholesterol synthesis inhibitors (simvastatin or squalestatin) prior to incubation with different neurotoxins. The effects of these drugs on neuronal cholesterol levels and neuronal survival were measured. Immunoblots were used to determine the effects of simvastatin or squalestatin on the distribution of the PAF receptor and an enzyme linked immunoassay was used to quantify the amounts of PAF receptor.

RESULTS

PAF killed primary neurons in a dose-dependent manner. Pre-treatment with simvastatin or squalestatin reduced neuronal cholesterol and increased the survival of PAF-treated neurons. Neuronal survival was increased 50% by 100 nM simvastatin, or 20 nM squalestatin. The addition of mevalonate restored cholesterol levels, and reversed the protective effect of simvastatin. Simvastatin or squalestatin did not affect the amounts of the PAF receptor but did cause it to disperse from within lipid rafts.

CONCLUSION

Treatment of neurons with cholesterol synthesis inhibitors including simvastatin and squalestatin protected neurons against PAF. Treatment caused a percentage of the PAF receptors to disperse from cholesterol-sensitive domains. These results raise the possibility that the effects of statins on neurodegenerative disease are, at least in part, due to desensitisation of neurons to PAF.

Structure–activity relationships in platelet-activating factor. Part 14: Synthesis and biological evaluation of piperazine derivatives with dual anti-PAF and anti-HIV-1 activity

As HIV-associated dementia prevalence has risen with the lifespan of HIV-infected individuals, there is an important need for antiretroviral and anti-inflammatory drugs targeting the central nervous system. Platelet-activating factor, a mediator of inflammation, is an HIV-induced neurotoxin secreted in the infected brain. In this work, we developed piperazine derivatives bearing a heterocyclic moiety as PAF-antagonists and HIV-1 replication inhibitors with micromolar potency.

Structure-activity relationships in platelet-activating factor. Part 13: synthesis and biological evaluation of piperazine derivatives with dual anti-PAF and anti-HIV-1 or pure antiretroviral activity

HIV-1 infection of the brain and PAF neurotoxicity are implicated in AIDS dementia complex. We previously reported that a trisubstituted piperazine derivative is able to diminish both HIV-1 replication in monocyte-derived macrophages and PAF-induced platelet aggregation. We report in this work new compounds obtained by modifying its piperazine substituents. The structure-activity relationship study shows that a better dual activity or even pure antiretroviral compounds can be obtained in this series.

Interaction of macrophages with apoptotic cells enhances HIV Type 1 replication through PGE2, PAF, and vitronectin receptor

Phagocytosis of apoptotic cells by macrophages increases secretion of soluble mediators and generates an antiinflammatory environment. We previously reported that phagocytosis of apoptotic cells by HIV-1-infected macrophages enhances viral replication, with the participation of the cytokine transforming growth factor- beta1 and an integrin receptor. Now, we describe the role of prostaglandin E2 (PGE2), platelet-activating factor (PAF), and the integrin alphaVbeta3 (vitronectin receptor, VnR) in this phenomenon. Exacerbation of HIV-1 growth induced by phagocytosis of apoptotic cells was inhibited when HIV-1-infected macrophages were treated with a cyclooxygenase 2 inhibitor, or with a PAF receptor antagonist (BN 52021) immediately after macrophage interaction with apoptotic cells. Treatment of HIV-1-infected macrophages with BN 52021 decreased viral replication, whereas addition of PGE2 or PAF to these cells enhanced viral replication. Monoclonal antibodies (MAbs) to VnR reduced the macrophage uptake of apoptotic cells, prevented the enhancement of HIV-1 growth upon the engulfment of apoptotic cells, and potently augmented viral replication in HIV-1-infected macrophages in the absence of apoptotic cells. In conclusion, PGE2 and PAF, and ligation of VnR as well, contribute to amplify viral growth in HIV-1-infected macrophages upon uptake of apoptotic cells.

Human immunodeficiency virus infection and acquired immunodeficiency syndrome dementia complex: role of cells of monocyte-macrophage lineage

The entry of human immunodeficiency virus (HIV) into the central nervous system (CNS) causes both the establishment of a lifelong viral reservoir in the brain and symptoms of neurological dysfunction that have an AIDS dementia complex (ADC) clinical appearance. Neurological dysfunction in ADC patients still remains an unresolved problem. However, ADC pathogenesis may be a multistep process that starts with HIV invasion of CNS by crossing the blood-brain barrier (BBB). It progresses by developing a chronic inflammatory status that can cause dysfunction in neurons and astrocytes that result in apoptotic death. Monocytes-macrophages (M/M) may play an important role by concealing the HIV transfer across the BBB. Furthermore, HIV-infected M/M could produce and release neurotoxic factors. In this review the main mediators and cells involved in pathogenesis and development of ADC are highlighted. A better understanding of the mechanisms involved in this process may help in a successful therapeutic approach to the neuropathogenesis of HIV infection.

Role of the pro-inflammatory cytokines TNF-alpha and IL-1beta in HIV-associated dementia

Human immunodeficiency virus-1 (HIV-1)-infected and immune-activated macrophages and microglia secrete neurotoxins. Two of these neurotoxins are the pro-inflammatory cytokines tumour necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta), which are thought to play a major role in inducing neuronal death. Both TNF-alpha and IL-1beta increase the permeability of the blood-brain barrier, through which subsequently HIV-infected monocytes can enter the brain. They both induce over-stimulation of the NMDA-receptor via several pathways, resulting in a lethal neuronal increase in Ca(2+) levels. Additionally, TNF-alpha co-operates with several other proinflammatory mediators to enhance their toxic effects. Although most research has focused on the neurotoxic effects of TNF-alpha and IL-1beta in HAD, there is also evidence that these cytokines can be neuroprotective. In this paper the effect of TNF-alpha and IL-1beta on neuronal life and death in HAD is discussed.

HIV-1-based defective lentiviral vectors efficiently transduce human monocytes-derived macrophages and suppress replication of wild-type HIV-1

BACKGROUND

Human monocytes play an important role in mediating human immunodeficiency virus type 1 (HIV-1) infection of the central nervous system (CNS), and monocytes-derived macrophages (MDM) represent a major viral reservoir within the brain and other target organs. Current gene transduction of MDM is hindered by a limited efficiency. In this study we established a lentiviral vector-based technique for improved gene transfer into human MDM cultures in vitro and demonstrated significant protection of transduced MDM from super-infection with wild-type HIV-1.

METHODS

HIV-1-based lentiviral vector stocks were prepared in 293T cells by the established calcium phosphate transfection method. Human monocytes were isolated from donors' blood by Ficoll-Paque separation and cultured in vitro. To establish an effective technique for vector-mediated gene transfer, primary cultures of human MDM were transduced at varying multiplicities of infection (MOI) and at a range of time points following initial isolation of cells (time-in-culture). Transduced cells were then examined for transgene (green fluorescent protein (GFP)) expression by fluorescent microscopy and reverse transcription polymerase chain reaction (RT-PCR). These cultures were then exposed to wild-type HIV-1, and viral replication was quantitated by p24 assay; production of neurotoxic effector molecules by the transduced MDM was also examined, using indicator neurons.

RESULTS

We have demonstrated that primary human MDM could be efficiently transduced (>50%) with concentrated HIV-1-based defective lentiviral vectors (DLV). Furthermore, DLV-mediated gene transduction was stable, and the transduced cells exhibited no apparent difference from normal MDM in terms of their morphology, viability and neurotoxin secretion. Challenge of DLV-transduced MDM cultures with HIV-1(Ba-L) revealed a 4- to 5-fold reduction in viral replication, as measured by p24 antigen production. This effect was associated with the mobilization of the GFP-expressing DLV construct by the wild-type virus.

CONCLUSIONS

These data demonstrate the inhibition of HIV-1 replication in primary MDM, by a DLV vector that lacks any anti-HIV-1 transgene. These findings lay the initial groundwork for future studies on the ability of DLV-modified monocytes to introduce anti-HIV-1 genes into the CNS. Lentiviral vector-mediated gene delivery to the CNS by monocytes/macrophages is a promising, emerging strategy for treating neuro-AIDS.