Cytokines and arachidonic metabolites produced during human immunodeficiency virus (HIV)-infected macrophage-astroglia interactions: implications for the neuropathogenesis of HIV disease.

Human immunodeficiency virus (HIV) infection of brain macrophages and astroglial proliferation are central features of HIV-induced central nervous system (CNS) disorders. These observations suggest that glial cellular interactions participate in disease. In an experimental system to examine this process, we found that cocultures of HIV-infected monocytes and astroglia release high levels of cytokines and arachidonate metabolites leading to neuronotoxicity. HIV-1ADA-infected monocytes cocultured with human glia (astrocytoma, neuroglia, and primary human astrocytes) synthesized tumor necrosis factor (TNF-alpha) and interleukin 1 beta (IL-1 beta) as assayed by coupled reverse transcription-polymerase chain reaction, enzyme-linked immunosorbent assay, and biological activity. The cytokine induction was selective, cell specific, and associated with induction of arachidonic acid metabolites. TNF-beta, IL-1 alpha, IL-6, interferon alpha (IFN-alpha), and IFN-gamma were not produced. Leukotriene B4, leukotriene D4, lipoxin A4, and platelet-activating factor were detected in large amounts after high-performance liquid chromatography separation and correlated with cytokine activity. Specific inhibitors of the arachidonic cascade markedly diminished the cytokine response suggesting regulatory relationships between these factors. Cocultures of HIV-infected monocytes and neuroblastoma or endothelial cells, or HIV-infected monocyte fluids, sucrose gradient-concentrated viral particles, and paraformaldehyde-fixed or freeze-thawed HIV-infected monocytes placed onto astroglia failed to induce cytokines and neuronotoxins. This demonstrated that viable monocyte-astroglia interactions were required for the cell reactions. The addition of actinomycin D or cycloheximide to the HIV-infected monocytes before coculture reduced, > 2.5-fold, the levels of TNF-alpha. These results, taken together, suggest that the neuronotoxicity associated with HIV central nervous system disorders is mediated, in part, through cytokines and arachidonic acid metabolites, produced during cell-to-cell interactions between HIV-infected brain macrophages and astrocytes.

1 alpha, 25-Dihydroxyvitamin D3 nuclear receptors in pituitary.

Specific binding of 1 alpha,25-dihydroxyvitamin D(3) was found in nuclear and cytosol fractions of the bovine pituitary. For nuclear binding. the dissociation constant was 0.1 namomole per liter, and maximum binding was 104 femtomoles per milligram of protein. In competition studies, 25-hydroxyvitamin D(3) was 300 times weaker than 1 alpha,25-dihydroxyvitamin D(3). The existence of high-affinity sites supports a physiologic role for 1 alpha,25-dihydroxyvitamin D(3) in the pituitary.

Tumor necrosis factor alpha-induced apoptosis in human neuronal cells: protection by the antioxidant N-acetylcysteine and the genes bcl-2 and crmA.

Tumor necrosis factor alpha (TNF-alpha) is a candidate human immunodeficiency virus type 1-induced neurotoxin that contributes to the pathogenesis of AIDS dementia complex. We report here on the effects of exogenous TNF-alpha on SK-N-MC human neuroblastoma cells differentiated to a neuronal phenotype with retinoic acid, TNF-alpha caused a dose-dependent loss of viability and a corresponding increase in apoptosis in differentiated SK-N-MC cells but not in undifferentiated cultures. Importantly, intracellular signalling via TNF receptors, as measured by activation of the transcription factor NF-kappa B, was unaltered by retinoic acid treatment. Finally, overexpression of bcl-2 or crmA conferred resistance to apoptosis mediated by TNF-alpha, as did the addition of the antioxidant N-acetylcysteine. These results suggest that TNF-alpha induces apoptosis in neuronal cells by a pathway that involves formation of reactive oxygen intermediates and which can be blocked by specific genetic interventions.

Seasonal mood disorders. Patterns of seasonal recurrence in mania and depression.

DSM-III-R criteria, applied retrospectively in a research-oriented psychiatric clinic, identified patients (N = 146) with a mood disorder and a seasonal pattern of recurrence (seasonal mood disorder). The seasonal mood disorder syndrome was not rare (10% of all mood disorders); diagnostic distribution was as follows: recurrent depression, 51%, and bipolar disorder, 49%, with 30% of the latter having mania (bipolar disorder type I) and 19% having hypomania (bipolar disorder type II). Most patients were women (71%); onset age averaged 29 years, with a mean of eight cycles in 12 years of illness; mean episode duration was 5.0 months. Mood disorder was found in a high proportion (68%) of the families. All but one patient followed one of two seasonal patterns in equal frequency: type A, fall-winter depression with or without spring-summer mania or hypomania; and type B, spring-summer depression with or without fall-winter mania or hypomania. Both types showed consistent times of onset and remission. These results emphasize that DSM-III-R seasonal mood disorder includes severe cases of recurrent depression and bipolar disorder and support a distinction between two seasonal subtypes.

Adjunctive therapies for HIV-1 associated neurologic disease.

In the past decade we have seen a milder phenotype and decreased incidence of HIV-1 associated dementia (HAD), largely due to the widespread use of combination chemotherapy to reduce viral burden. However, the prevalence of neurologic disease in people living with HIV-1 has actually increased, raising significant concerns that new therapeutic strategies, directed at restoring neuronal and glial homeostasis and signaling in the central nervous system (CNS), as opposed to directly interfering with the life cycle of HIV-1, must be developed. In this review, we focus briefly on previous Phase 1 clinical trials for adjunctive (i.e., chemotherapeutic agents that do not have a primary antiretroviral mechanism of action) therapy in patients with HAD, followed by an overview of key molecular events in the neuropathogenesis of HAD, and then discuss in more detail our rationale for investigating the effects of therapeutic agents that restore impaired mitochondrial bioenergetics in the CNS. Specifically, we focus on agents that either work in part through K-ATP channels, present in both mitochondria and plasma membranes, and agents that work to weakly uncouple the respiratory capacity of the electron transport chain in mitochondria from ATP production. We propose these agents may be complementary to currently available antiretroviral agents and may significantly improve the capacity of CNS infected with HIV-1 to meet increased bioenergetic demands involved in normal synaptic communication.

HIV-1-induced neuronal injury in the developing brain.

HIV-1 infection of the nervous system causes neuronal injury and death, resulting in cognitive, motor, and behavioral dysfunction in both adults and children. In infants a characteristic feature of HIV-1 infection is impaired brain growth resulting in secondary microcephaly with onset between 2 and 4 months of age. This post-natal period of brain development is particularly vulnerable to excitotoxic neuronal injury due to the active synaptogenesis and pruning that takes place at this age associated with over-expression of excitatory amino acid (EAA) receptors. HIV-1 infection of brain microglia and perivascular macrophages results in chronic inflammation manifest pathologically as diffuse microglial activation and reactive astrogliosis. Several inflammatory products of activated microglia, including tumor necrosis factor alpha (TNF-alpha) and platelet-activating factor (PAF) have been shown to act as neuronal toxins. This toxic effect can be antagonized by blocking NMDA (or AMPA) glutamate receptors, suggesting that (weak) excitotoxicity leads to oxidative stress, neuronal injury, and apoptosis. HIV-1 infection and chronic inflammation may also contribute disruption of the blood-brain barrier and could result in further entry into the CNS of toxic viral or cellular products or additional HIV-1-infected cells. We hypothesize that prolonged microglial activation during HIV-1 infection underlies the neuronal injury and impaired brain growth in affected infants. Further investigation of the interaction between HIV-1-infected/activated microglia and developing neurons seems warranted. The current understanding of HIV neuropathogenesis implies that therapeutic strategies should target the sustained immune activation in microglia, attempt to repair the integrity of the blood-brain barrier, and provide "neuroprotection" from excitotoxic neuronal injury.

Excitotoxicity and dopaminergic dysfunction in the acquired immunodeficiency syndrome dementia complex. Therapeutic implications.

Human immunodeficiency virus infection is frequently complicated by a syndrome of central nervous system dysfunction known as the acquired immunodeficiency syndrome dementia complex (ADC). The ADC is characterized by abnormalities in cognition, motor performance, and behavior, and it produces serious morbidity in a significant number of patients with acquired immunodeficiency syndrome. The pathogenesis of ADC is unclear, but appears to be caused by the human immunodeficiency virus itself, rather than by a secondary opportunistic process. Herein, we review the data regarding the pathogenesis of ADC and hypothesize a mechanism involving excitotoxicity and dopaminergic dysfunction. N-methyl-D-aspartate receptor antagonists may be of therapeutic benefit, as these agents may both limit glutamate-mediated neuronal dysfunction and improve dopaminergic neuronal function.

Developmental differences in acute nigrostriatal and mesocorticolimbic system response to haloperidol.

Dose-dependent effects of haloperidol (2.66 nmol/kg to 79.8 mmol/kg, IP) on levels of dopamine, homovanillic acid (HVA) and dihydroxyphenylacetic acid (DOPAC) were assessed in the corpus striatum, nucleus accumbens, and medial prefrontal cortex (PFCTX) of 18-, 30-, and 110-day-old rats. Eighteen-day-old rats were 35% and 63% more sensitive than adults to the effects of haloperidol on striatal and accumbens turnover and had steeper dose-response curves. The dose-response function in the PFCTX was similar to striatum at 18 days, but became shallower and nonsigmoidal with age. Maximally effective doses of haloperidol produced, at all ages, a comparable percent rise in DOPAC levels in all regions. With maturation, the percent rise in HVA progressively outstripped DOPAC response in nucleus accumbens and striatum. Overall, prominent developmental differences emerged in these regions in their sensitivity and response to haloperidol, which are consistent with previously reported differences in behavioral sensitivity.

Proteasome blockers inhibit TNF-alpha release by lipopolysaccharide stimulated macrophages and microglia: implications for HIV-1 dementia.

HIV-1 infection of the central nervous system can cause severe neurologic disease although only microglial cells and brain macrophages are susceptible to productive viral infection. Substances secreted by infected cells are thought to cause disease indirectly. Tumor necrosis factor alpha (TNF-alpha) is one candidate neurotoxin and is upregulated during HIV-1 infection of the brain, likely via activation of the transcription factor NF-kappaB. We used the proteasome inhibitors, MG132 and ALLN (N-acetyl-Leu-Leu-Norleucinal), to inhibit NF-kappaB activation in primary human fetal microglia (PHFM) and primary monocyte derived-macrophages, and showed that they could block TNF-alpha release stimulated by lipopolysaccharide (LPS) or TNF-alpha. In addition, we performed electrophoretic mobility shift analysis and determined that in microglia, the p50/p65 heterodimer of NF-kappaB is activated by LPS stimulation, and is inhibited by MG132. Thus, blockade of NF-kappaB activation in microglia in vitro can decrease production of TNF-alpha and may prove to be a novel strategy for treating HIV-1 dementia.

Intracellular CXCR4 signaling, neuronal apoptosis and neuropathogenic mechanisms of HIV-1-associated dementia.

The mechanism(s) by which HIV-1 affects neural injury in HIV-1-associated dementia (HAD) remains unknown. To ascertain the role that cellular and viral macrophage products play in HAD neurotoxicity, we explored one potential route for neuronal demise, CXCR4. CXCR4, expressed on lymphocytes and neurons, is both a part of neural development and a co-receptor for HIV-1. Its ligand, stromal cell-derived factor-1alpha (SDF-1alpha), affects neuronal viability. GTP binding protein (G-protein) linked signaling after neuronal exposure to SDF-1alpha, virus-infected monocyte-derived macrophage (MDM) secretory products, and virus was determined. In both human and rat neurons, CXCR4 was expressed at high levels. SDF-1alpha/beta was detected predominantly in astrocytes and at low levels in MDM. SDF-1beta/beta was expressed in HAD brain tissue and upregulated in astrocytes exposed to virus infected and/or immune activated MDM conditioned media (fluids). HIV-1-infected MDM secretions, virus and SDF-1beta induced a G inhibitory (Gi) protein-linked decrease in cyclic AMP (cAMP) and increase inositol 1,4, 5-trisphosphate (IP3) and intracellular calcium. Such effects were partially blocked by antibodies to CXCR4 or removal of virus from MDM fluids. Changes in G-protein-coupled signaling correlated, but were not directly linked, to increased neuronal synaptic transmission, Caspase 3 activation and apoptosis. These data, taken together, suggest that CXCR4-mediated signal transduction may be a potential mechanism for neuronal dysfunction during HAD.

Simultaneous in situ detection of apoptosis and necrosis in monolayer cultures by TUNEL and trypan blue staining.

A method for simultaneously detecting membrane permeability (characteristic of necrosis) and DNA fragmentation (characteristic of apoptosis) is described. By combining a common dye-exclusion method (Trypan Blue) with a commercially available terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end-labeling (TUNEL) labeling kit, we have succeeded in developing a novel methodology for obtaining permanently mounted slides of monolayer cell cultures double-labeled for DNA fragmentation and cell lysis. This method should facilitate in situ studies of cell death by allowing for a more accurate quantification of total toxicity in monolayer cell cultures and perhaps further enhance our understanding of the different mechanisms of cell death as well.

HIV-1 infection of the developing nervous system: central role of astrocytes in pathogenesis.

Recent studies in our laboratory and that of Dr. Howard Gendelman have revealed two important pathways for neuronal damage during HIV-1 encephalopathy in children. First, substantial numbers of astrocytes are actively or latently infected with HIV-1. Astrocyte infection may lead to neuronal dysfunction through loss of supporting growth factors, excitotoxicity due to dysregulation of neurotransmitter reuptake, and loosening of the blood-brain barrier permitting further seeding of HIV-1 in the CNS. Significantly, infection of astrocytes is marked by near-exclusive synthesis of early regulatory gene products of HIV-1, while structural proteins characteristic of productive infection are found in macrophages, microglia and multinucleated giant cells. We propose the term 'restricted' to denote the non-productive infection found in astrocytes. Second, HIV-1-infected macrophages initiate inflammatory processes which are amplified through cell-cell interactions with astrocytes. Macrophage-astrocyte interactions produce arachidonic metabolites and potentially neurotoxic cytokines (TNF-alpha and IL-1 beta), leading to astroglial activation and proliferation which then amplifies these cellular processes. These new findings suggest that two major pathways leading to neurotoxicity in pediatric AIDS encephalopathy are linked to HIV-1 infection through astrocyte-mediated processes, and help explain how small numbers of productivity infected cells indirectly cause widespread tissue pathology and elicit profound neurological impairment.

In situ amplification and detection of HIV-1 DNA in fixed pediatric AIDS brain tissue.

To examine whether latent infection by HIV-1 occurs in the central nervous system, we optimized a procedure for amplification and detection of HIV-1 DNA in situ, in formalin-fixed brain tissue from a child with severe HIV-1-associated progressive encephalopathy and severe HIV-1 encephalitis. By the use of a two-step technique, which involved polymerase chain reaction with incorporation of digoxigenin-labeled nucleotides followed by in situ hybridization with biotinylated probes, we found infection of numerous mononuclear cells and astrocytes in the cerebral white matter as well as of perineuronal satellite cells in basal ganglia, but not of neurons. Following PCR amplification, nuclear signal was found in 10 to 20 times as many cells as in parallel, control experiments using conventional, unamplified in situ hybridization.

Luciferase: a sensitive and quantitative probe for blood-brain barrier disruption.

A novel method for quantitative analysis of blood-brain barrier (BBB) disruption is described, using luciferase as a probe in a murine model system. Purified luciferase was delivered to mouse brain by osmotic BBB disruption with hypertonic mannitol; control animals received an intracarotid inoculation of saline prior to infusion of luciferase. Delivery of luciferase to brain tissue was then assessed by enzyme assay of tissue extracts, and by immunohistochemical staining. Luciferase activity in the brain of mannitol-treated animals was found to be significantly elevated (approx. sevenfold), when compared to activity in control (saline-treated) mice. This finding was confirmed by quantitative immunohistochemical staining of tissue sections, using a luciferase-specific antibody. These studies showed that there was an eight-fold elevation in the level of extravascular luciferase particles within the brain of mannitol-treated animals, as compared to controls. Taken together these data show that purified recombinant luciferase can be used as a sensitive probe, with which to study the integrity of the BBB.

Paraquat elicited neurobehavioral syndrome caused by dopaminergic neuron loss.

The herbicide paraquat, bearing structural similarity to the known dopaminergic neurotoxicant MPTP, has been suggested as a potential etiologic factor in Parkinson's disease. Consideration of paraquat as a candidate neurotoxicant requires demonstration that systemic delivery produces substantia nigra dopaminergic neuron loss and the attendant neurobehavioral syndrome reflecting depletion of dopamine terminals within the striatum. To address these issues paraquat was administered systemically into adult C57 bl/6 mice, ambulatory behavior monitored, substantia nigra dopamine neuron number and striatal dopamine terminal density quantified. The data indicate that paraquat like MPTP elicits a dose-dependent decrease in substantia nigra dopaminergic neurons assessed by a Fluoro-gold prelabeling method, a decline in striatal dopamine nerve terminal density assessed by measurement of tyrosine hydroxylase immunoreactivity; and neurobehavioral syndrome characterized by reduced ambulatory activity. Taken together, these data suggest that systemically absorbed paraquat crosses the blood-brain barrier to cause destruction of dopamine neurons in the substantia nigra, consequent reduction of dopaminergic innervation of the striatum and a neurobehavioral syndrome similar to the well characterized and bona fide dopaminergic toxin MPTP.

Postnatal development of dopamine D1 and D2 receptor sites in rat striatum.

Tissue was obtained from corpus striatum of maturing rats at representative postnatal ages of 8-120 days for evaluation of D1 and D2 dopamine (DA) receptor sites in radioreceptor assays based on use of 0.05-2.5 nM concentrations of [3H]SCH-23390 or [3H]domperidone, respectively. Pharmacologic selectivity was verified by high rank-correlations (rs greater than 0.90) of Ki values for representative test agents in both assays (vs 0.3 nM ligand), using striatal tissue obtained at ages 20 and 120 days. Data from repeated (3-5x) six-concentration isotherm experiments involving a wide range of D1 or D2 radioligand concentrations were analyzed by linear regression of specific binding (B) vs free ligand concentration (F) in linearized form (B/F vs B) for each replicate assay and for pooled values, as well as by curve-fitting all available raw data (B vs F) using the LIGAND program adapted to microcomputer. Values for apparent ligand affinity (Kd = 0.15-0.35 nM) failed to show a consistent change with age, while values for apparent receptor site density (Bmax) followed a similar developmental course with both methods of analysis (between methods: r = 0.99 and 0.89 for D1 and D2 assays, respectively, across all ages tested).(ABSTRACT TRUNCATED AT 250 WORDS)

Dopamine D1 receptor development depends on endogenous dopamine.

Profound depletion of forebrain dopamine by 6-hydroxydopamine in neonatal rats (day 3) was associated with up to 82% loss of D1 receptor sites labeled with [3H]SCH-23390 at day 21. Administration of the selective D1 agonist SKF-38393 (days 6-18) abolished the correlation between D1 receptor density and DA concentrations, even with greater than 99% depletion of DA. In intact control animals, there was an inverse correlation between spontaneous variation in levels of DA and D1 receptor site density in forebrain tissue (r = -0.79) which also was abolished by treatment with the D1 agonist. Thus, D1 receptor density may be regulated by reciprocal regulatory processes during normal development, but may fail to develop in the absence of an adequate level of stimulation.

Dopamine D1 autoreceptor function: possible expression in developing rat prefrontal cortex and striatum.

Synthesis-modulating dopamine (DA) autoreceptor function was studied in vivo using gamma-butyrolactone (GBL) to block propagation along DA axons. DA synthesis was measured by the accumulation of L-3,4-dihydroxyphenylalanine (L-DOPA) after inhibition of aromatic L-amino acid decarboxylase. GBL treatment markedly increased DOPA accumulation in both the striatum and prefrontal cortex of developing rats. The selective DA partial D1 agonist SKF-38393 inhibited this GBL-induced rise in DA synthesis in both the striatum and prefrontal cortex of 15- and 22-day-old rats, but not in adults. The effects of SKF-38393 in developing rats were mimicked by the non-catechol D1 partial agonist CY-208-243, and were blocked by the D1 antagonist SCH-23390, suggesting receptor mediation. The mixed D2/D3 agonist quinpirole attenuated DA synthesis in striatum of both two-week-old and adult rats, but failed to inhibit the GBL-induced increase in DA synthesis in the developing prefrontal cortex. These findings suggest that synthesis-modulating D1-like receptor function may emerge transiently in the developing mammalian forebrain. In the adult striatum these functions appear to be subsumed by D2-like receptors, whereas all synthesis-modulating DA receptor function in prefrontal cortex appears to be essentially lost with maturation.

Progressive accumbens degeneration after neonatal striatal 6-hydroxydopamine in rats.

Parkinson's disease is associated with progressive loss of nigrostriatal dopamine (DA). Models of the disorder, produced with neurotoxins (N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine or 6-hydroxydopamine) that selectively lesion DA neurons, are characterized by acute removal and gradual recovery of DA. We report slowly progressive loss of DA in ipsilateral nucleus accumbens following profound (>90%) acute unilateral depletion of DA in the caudate-putamen of neonatal rats, from 50% at age 27 days to 94% by 100 days. Metabolic turnover of DA markedly increased in ipsilateral accumbens, and may yield tissue-damaging neurotoxic by-products. This paradigm may help in elucidating mechanisms responsible for gradual degeneration of DA neurons and for screening potential neuroprotective agents.

Persistent increases in dopamine D2 receptor mRNA expression in basal ganglia following kindling.

Amygdala kindling resulted in significant increases in the expression of D2 receptor mRNA in the nucleus accumbens and striatum 30 days following the last kindling stimulation. Densitometric analyses of tissue sections incubated in the presence of an oligonucleotide probe directed against D2 receptor cDNA indicated a 20-35% increase in D2 receptor mRNA in these regions following kindling. Kindling from the amygdala followed by piriform cortical kindling in the transfer paradigm (overkindling) resulted in significant further increases in D2 receptor mRNA expression in both the accumbens (150% increase) and striatum (120% increase). There were no observed hemispheric asymmetries in D2 receptor mRNA in either kindled or overkindled animals. The data indicate an enduring upregulation of extrapyramidal D2 receptor mRNA following the kindling process. How this change may relate to kindling-induced alterations in seizure susceptibility or behaviors mediated by limbic dopaminergic pathways are questions for future studies.