Biomarkers of HIV-1 CNS infection and injury

While it is clear that HIV-1 can cause CNS dysfunction, current approaches to classification and diagnosis of this dysfunction rely on syndromic definitions or measures of abnormality on neuropsychological testing in the background context of HIV-1 infection. These definitions have been variably applied, offer only limited sensitivity or specificity, and do not easily distinguish active from static brain injury. Supplanting or augmenting these approaches with objective biologic measurements related to underlying disease processes would provide a major advance in classification, diagnosis, epidemiology, and treatment assessment. Two major avenues are now actively pursued to this end: 1) analysis of soluble molecular markers in CSF and, to a lesser degree, in blood, and 2) neuroimaging markers using anatomic, metabolic, and functional measurements. This review considers the rationale and prospects of these approaches.

Whole brain and localized magnetization transfer measurements are associated with cognitive impairment in patients infected with human immunodeficiency virus

BACKGROUND AND PURPOSE

Patients infected with human immunodeficiency virus (HIV) are susceptible to cognitive deterioration. This study investigated the utility of magnetization transfer (MT) imaging for quantification of brain tissue alterations associated with cognitive deficits in patients with HIV.

MATERIALS AND METHODS

MT ratios (MTR) were derived for whole brain and for regions of interest (ROIs) in the basal ganglia and white matter in 11 HIV and 12 control subjects. Relationships with severity of cognitive impairment and specific neuropsychological deficits were also evaluated.

RESULTS

MTR values for normalized whole brain histogram peak height, whole brain histogram mean, and all examined ROIs were reduced in the HIV subjects. Normalized histogram peak height and mean for whole brain, as well as means for the corpus callosum, basal ganglia, and frontal white matter (FWM), were significantly correlated with severity of cognitive impairment. MTR values for white matter regions (corpus callosum, FWM, and centrum semiovale) were correlated with specific cognitive deficits.

CONCLUSION

Quantitative MTR measurements, determined for the whole brain and for vulnerable ROIs, are sensitive to neuropathologic changes associated with cognitive impairment in HIV-infected patients.

Updated research nosology for HIV-associated neurocognitive disorders

In 1991, the AIDS Task Force of the American Academy of Neurology published nomenclature and research case definitions to guide the diagnosis of neurologic manifestations of HIV-1 infection. Now, 16 years later, the National Institute of Mental Health and the National Institute of Neurological Diseases and Stroke have charged a working group to critically review the adequacy and utility of these definitional criteria and to identify aspects that require updating. This report represents a majority view, and unanimity was not reached on all points. It reviews our collective experience with HIV-associated neurocognitive disorders (HAND), particularly since the advent of highly active antiretroviral treatment, and their definitional criteria; discusses the impact of comorbidities; and suggests inclusion of the term asymptomatic neurocognitive impairment to categorize individuals with subclinical impairment. An algorithm is proposed to assist in standardized diagnostic classification of HAND.

Monocyte chemoattractant protein-1 correlates with subcortical brain injury in HIV infection

Various biomarkers have been suggested as associative or predictive of HIV-associated neurocognitive impairment. Plasma levels of monocyte chemoattractant protein 1 (MCP-1), tumor necrosis factor alpha (TNF-alpha), and hematocrit were evaluated for relationships with diffusion tensor imaging measurements of centrum semiovale, caudate, and putamen. MCP-1 levels correlated with tissue status (mean diffusivity) in all examined regions. Plasma markers were also significantly correlated with anisotropy measurements in centrum semiovale (TNF-alpha) and putamen (hematocrit).

Diffusion alterations in corpus callosum of patients with HIV

BACKGROUND AND PURPOSE

Diffusion alterations have been identified in the corpus callosum and frontal white matter of patients infected with human immunodeficiency virus (HIV), though the relevance of these findings to cognitive deterioration has not yet been determined. This study tested the hypothesis that diffusion tensor imaging can detect tissue status alterations in these regions in cognitively impaired patients infected with HIV and the acquired measurements correlate with the severity of cognitive impairment.

METHODS

Fractional anisotropy (FA) and mean diffusivity (MD) were determined for corpus callosum (genu and splenium) and frontal white matter (FWM). The DTI measurements were compared in 11 HIV and 11 control participants. Patterns of relationship were examined with cognitive status measures from concurrent neurologic and neuropsychologic evaluations.

RESULTS

FA values for the splenium were significantly reduced in the patients infected with HIV and correlated with dementia severity and deficits in motor speed. MD values for the splenium were significantly increased in the patients infected with HIV and correlated with deficits in motor speed. FA measurements were also significantly correlated with performance on visual memory (genu), visuoconstruction (FWM), and verbal memory (FWM) tasks.

CONCLUSION

Diffusion abnormalities were identified in the splenium of the corpus callosum in patients infected with HIV, and these alterations were associated with dementia severity and motor speed losses. In vivo assessment of callosal integrity by using quantitative neuroimaging may have potential utility as a marker of brain injury in patients infected with HIV.

Bone marrow diffusion measures correlate with dementia severity in HIV patients

BACKGROUND AND PURPOSE

Escalation in monocyte trafficking from the bone marrow into the brain may play a critical role in central nervous system injury and cognitive deterioration in patients with HIV infection. This study tested the hypothesis that the mean diffusivity is sensitive to marrow changes in HIV patients and that these quantitative imaging measurements correlate with the severity of dementia.

METHODS

The mean diffusivity (MD), determined for clival and calvarial marrow regions, was compared in 11 HIV-infected patients and 9 control subjects. The imaging measurements were also evaluated for relationships with dementia severity and markers of disease progression (CD4 and viral load in plasma).

RESULTS

The MD was significantly reduced in both clival and calvarial marrow in HIV-infected patients (P =.006). Diffusion measurements for clival (P =.02) and for calvarial (P =.03) regions were significantly correlated with the severity of dementia.

CONCLUSION

The results of this investigation support the utility of diffusion strategies for monitoring the marrow and provide further evidence of a relationship between marrow status changes and neurologic progression in HIV patients.

Markers of immune activation and viral load in HIV-associated sensory neuropathy

BACKGROUND

HIV infection is associated with a painful distal sensory polyneuropathy (DSP) that can severely limit the quality of life of affected subjects. The pathogenesis of DSP is unknown, although both HIV proteins and products of immune activation triggered by HIV infection have been implicated.

OBJECTIVE

To assess the association between baseline markers of immune activation and HIV RNA levels (viral load) and time to symptomatic DSP (SDSP).

METHODS

A cohort of 376 subjects, most receiving highly active antiretroviral therapy (HAART), were followed semiannually for up to 48 months. Blood and CSF levels of HIV viral load, monocyte chemotactic protein-1, macrophage colony-stimulating factor (M-CSF), matrix metalloproteinase-2, and tumor necrosis factor-alpha were measured in addition to CD4 lymphocyte cell count.

RESULTS

In subjects without SDSP at baseline (62.5% of the cohort), among the virologic and immunologic markers, only baseline CSF M-CSF levels were associated with time to SDSP (hazard ratio = 2.97, p = 0.05). The Kaplan-Meier estimate of the 1-year incidence of SDSP was 21%, a 15% decrease from that observed in the Dana cohort, a pre-HAART cohort enrolled with the same inclusion/exclusion criteria.

CONCLUSION

Highly active retroviral therapy (HAART) has changed the natural history of HIV-associated symptomatic distal sensory polyneuropathy (SDSP), which may explain, in contrast with studies from the pre-HAART era, the lack of association between SDSP and baseline HIV viral load and CD4 cell count.

Disease burden in HIV-associated cognitive impairment: a study of whole-brain imaging measures

OBJECTIVE

To study whole-brain MR measures derived from diffusion tensor imaging and magnetization transfer imaging (MTI) for the in vivo assessment of cumulative neuropathologic changes in HIV and to evaluate the quantitative imaging strategies with respect to cognitive status measures including the severity of dementia and the degree of impairment in specific cognitive domains including attention, memory, constructional abilities, and motor speed.

METHODS

Quantitative whole-brain measurements, including fractional anisotropy (FA), apparent diffusion coefficient (ADC), and magnetization transfer ratio (MTR), were derived from histograms and compared in HIV and control participants. Relationships between the MR and cognitive status measures were examined.

RESULTS

Whole-brain FA and MTR were reduced in patients with HIV and correlated with dementia severity. Whole-brain MTR and ADC were correlated with psychomotor deficits. Evaluation of relationships between the studied MR measures indicated a correlation between ADC and MTR; FA was not correlated with either ADC or MTR.

CONCLUSIONS

Findings from this investigation support the use of quantitative whole-brain MR measures for evaluation of disease burden in HIV. Reductions in whole-brain fractional anisotropy and magnetization transfer ratio (MTR) distinguished HIV and control subjects, and these measures were associated with dementia severity. Relationships were identified between whole-brain MTR and apparent diffusion coefficient and psychomotor deficits. Combining these quantitative strategies in neuroimaging examinations may provide more comprehensive information concerning ongoing changes in the brains of HIV patients.

Evaluation of HIV RNA and markers of immune activation as predictors of HIV-associated dementia

OBJECTIVE

To evaluate whether baseline levels of plasma and CSF HIV RNA, tumor necrosis factor alpha (TNFalpha), monocyte chemoattractant protein-1 (MCP-1), matrix metalloproteinase-2 (MMP-2), or macrophage colony stimulating factor (M-CSF) are predictors of incident HIV-associated dementia (HIVD) in a cohort with advanced HIV infection.

METHODS

A total of 203 nondemented subjects with CD4 lymphocyte counts less than 200/muL, or <300/microL but with cognitive impairment, underwent semiannual neurologic, cognitive, functional, and laboratory assessments. HIVD and minor cognitive motor disorder (MCMD) were defined using American Academy of Neurology criteria. The cumulative incidence of HIVD was estimated using Kaplan-Meier curves. Cox proportional hazards regression models were used to examine the associations between biologic variables and time to HIVD, adjusting for age, sex, years of education, duration of HIV infection, type of antiretroviral use, premorbid IQ score, and presence of MCMD.

RESULTS

After a median follow-up time of 20.7 months, 74 (36%) subjects reached the HIVD endpoint. The dementia was mild in 70% of cases. The cumulative incidence of HIVD was 20% at 1 year and 33% at 2 years. Highly active antiretroviral therapy (HAART) was used by 73% of subjects at baseline. A plasma HIV RNA level was undetectable in 23% of subjects and a CSF HIV RNA level was undetectable in 48% of subjects. In adjusted analyses, neither plasma nor CSF HIV RNA levels (log10) were associated with time to HIVD; log10 levels of plasma TNFalpha (HR 3.07, p = 0.03) and CSF MCP-1 (HR = 3.36, p = 0.06) tended to be associated with time to HIVD.

CONCLUSION

The lack of association between baseline plasma and CSF HIV RNA levels and incident dementia suggests highly active antiretroviral therapy may be affecting CNS viral dynamics, leading to lower HIV RNA levels, and therefore weakening the utility of baseline HIV RNA levels as predictors of HIV-associated dementia.

Inter-rater reliability of a clinical staging of HIV-associated cognitive impairment

OBJECTIVE

To determine the inter-rater reliability of a modification of the Memorial Sloan-Kettering (MSK) Staging for HIV-associated cognitive impairment.

METHODS

Data were abstracted on neurologic, neuropsychological, and functional status on 100 individuals participating at four sites in the Northeast AIDS Dementia (NEAD) Consortium cohort study, a longitudinal study of predictors of cognitive impairment in HIV-infected individuals. Neuropsychological performance was defined 1) based on the neuropsychologist's global impression and 2) solely based on neuropsychological test scores. Raters at each site used the abstracted data to assign an MSK stage to each subject blind to any identifying information. Inter-rater reliability was assessed using kappa statistics. Agreement between computer-generated ratings and site-generated ratings was also assessed.

RESULTS

Kappa statistics for pair-wise agreement among the sites regarding MSK stage ranged from 0.70-0.91, representing good to excellent agreement between sites. Agreement between computer-generated ratings and site-generated ratings was in the good to excellent range (0.62-0.79).

CONCLUSIONS

The authors have modified the MSK rating scale and developed a reliable instrument that can be used in multicenter studies. This instrument will be useful in staging HIV-dementia in future longitudinal studies and will be valuable in increasing accuracy of clinicopathologic studies.

Release of the neuronal glycoprotein ICAM-5 in serum after hypoxic-ischemic injury

Intercellular adhesion molecule (ICAM)-5 (telencephalin) is unique among the ICAMs, because it is only expressed in somatodendritic membranes of telencephalic neurons. To investigate the fate of ICAM-5 during focal brain injury, we induced hypoxia-ischemia (HI) damage in adult mice by right common carotid artery ligation followed by hypoxia. ICAM-5 was detectable in serum within a 48-hour window after HI injury. In HI brain, dendritic ICAM-5 immunore-activity was abolished, but it was present in the neuropil and soma of hippocampal pyramidal, dentate granule, and some cortical and striatal neurons. After HI injury, levels of ICAM-5 protein and messenger RNA initially increased, and ICAM-5 messenger RNA expression then decreased, although protein levels continued to increase. Because HI injury induces microglial activation with increases in CD11a/CD18 (lymphocyte function antigen [LFA]-1) counterreceptors to ICAM-5, we investigated whether modulation of interactions between LFA-1 receptors and brain ICAM-5 during HI injury are associated with changes in levels of serum ICAM-5. Intracerebroventricular administration of lipopolysaccharide to activate microglia before HI injury resulted in elevated serum ICAM-5 levels compared with those in mice with only HI injury. Pretreatment with anti-LFA-1 antibodies before HI injury or LFA-1 receptor knockout mice with HI injury had markedly reduced levels of serum ICAM-5. Lipopolysaccharide levels increased, whereas LFA-1 receptor blockade or LFA-1 knockout decreased HI injury in the first 12 hours. These data suggest that during the necrotic phase of HI injury, serum ICAM-5 may be a potential marker for somatodendritic neuronal damage.

Neuronal fractalkine expression in HIV-1 encephalitis: roles for macrophage recruitment and neuroprotection in the central nervous system

HIV-1 infection of the brain results in chronic inflammation, contributing to the neuropathogenesis of HIV-1 associated neurologic disease. HIV-1-infected mononuclear phagocytes (MP) present in inflammatory infiltrates produce neurotoxins that mediate inflammation, dysfunction, and neuronal apoptosis. Neurologic disease is correlated with the relative number of MP in and around inflammatory infiltrates and not viral burden. It is unclear whether these cells also play a neuroprotective role. We show that the chemokine, fractalkine (FKN), is markedly up-regulated in neurons and neuropil in brain tissue from pediatric patients with HIV-1 encephalitis (HIVE) compared with those without HIVE, or that were HIV-1 seronegative. FKN receptors are expressed on both neurons and microglia in patients with HIVE. These receptors are localized to cytoplasmic structures which are characterized by a vesicular appearance in neurons which may be in cell-to-cell contact with MPs. FKN colocalizes with glutamate in these neurons. Similar findings are observed in brain tissue from an adult patient with HIVE. FKN is able to potently induce the migration of primary human monocytes across an endothelial cell/primary human fetal astrocyte trans-well bilayer, and is neuroprotective to cultured neurons when coadministered with either the HIV-1 neurotoxin platelet activating factor (PAF) or the regulatory HIV-1 gene product Tat. Thus focal inflammation in brain tissue with HIVE may up-regulate neuronal FKN levels, which in turn may be a neuroimmune modulator recruiting peripheral macrophages into the brain, and in a paracrine fashion protecting glutamatergic neurons.

Expression of caspase-3 in brains from paediatric patients with HIV-1 encephalitis

Apoptosis of neurones, macrophages, and microglia occurs in the brains of paediatric patients with human immunodeficiency virus (HIV) type 1 encephalitis, which is often associated with pre-mortem neurological disease (progressive encephalopathy). We have previously reported that TUNEL-positive neurones in brain tissue from paediatric patients with HIV type 1 encephalitis and progressive encephalopathy are strikingly devoid of the pro-apoptotic gene product Bax, in marked contrast to brain-resident macrophages and microglia. Using immunocytochemical methods, the present study demonstrate that neurones in patients with HIV type 1 encephalitis and progressive encephalopathy, as well as macrophages and microglia, but not astrocytes, overexpress caspase-3, a pro-apoptotic enzyme that is proteolytically activated downstream of Bax-Bcl-2 dysregulation. Co-localization of neuronal cytoplasmic caspase-3 and nuclear TUNEL staining, a marker for fragmented DNA, was also infrequently observed in brain tissue from patients with HIV type 1 encephalitis and progressive encephalopathy. These findings suggest that vulnerable neurones in brain tissue from patients with HIV virus type 1 encephalitis and progressive encephalopathy undergo apoptosis by a mechanism that involves upregulation of caspase-3 in a pathway that is independent of Bax-Bcl-2 dysregulation. Furthermore, caspase-3 upregulation in apoptotic neurones likely occurs prior to DNA fragmentation.

Association of human herpesvirus 6 with the demyelinative lesions of progressive multifocal leukoencephalopathy

Progressive Multifocal Leukoencephalopathy (PML) is a primary demyelinating disease of the central nervous system occurring almost exclusively in individuals with impaired cell-mediated immunity. The JC polyoma virus has been accepted as the etiologic agent ofPML. Using a two-step in-situ polymerase chain reaction procedure to amplify and detect genomic DNA of human herpesvirus-6 (HHV6) in formalin-fixed paraffin-embedded archival brain tissues, a high frequency of infected cells was consistently detected in PML white matter both within and surrounding demyelinative lesions and HHV6 genome was found mainly within oligodendrocytes. Lesser amounts of HHV6 genome were detected in most normal, AIDS, and other neurological disease control tissues. Immunocytochemistry for HHV6 antigens showed actively infected nuclei of swollen oligodendrocytic morphology only within the demyelinative lesions of PML but not in adjacent uninvolved tissue. In addition, no HHV6 antigens were detectable in control tissues including brains of individuals with HIV-1 encephalopathy but without PML. Double immunohistochemical staining for JC virus large T antigen and HHV6 antigens demonstrated co-labeling of many swollen intralesional oligodendrocytes in the PML cases. The evidence suggests that HHV6 activation in conjunction with JC virus infection is associated with the demyelinative lesions of PML.

Randomized trial of the platelet-activating factor antagonist lexipafant in HIV-associated cognitive impairment. Neurological AIDS Research Consortium

OBJECTIVE

To assess the safety and tolerability of lexipafant in HIV-associated cognitive impairment.

BACKGROUND

Cognitive impairment is the most common neurologic complication of advanced HIV-1 infection. There is evidence that a variety of inflammatory mediators, including platelet-activating factor (PAF), may contribute to neuronal injury. We hypothesized that lexipafant, a PAF antagonist, might improve cognitive dysfunction in HIV-infected people.

METHODS

We conducted a randomized, double-blind, placebo-controlled clinical trial to assess the safety and tolerability of lexipafant 500 mg/day. The primary outcome measure for tolerability was the ability to complete the study on the originally assigned dosage of medication. Thirty patients with cognitive impairment were enrolled.

RESULTS

Lexipafant was safe and well tolerated. Ninety-three percent in the placebo group and 88% in the lexipafant group completed the study at the originally assigned dosage. Trends toward improvement were seen in neuropsychological performance, especially verbal memory, in the lexipafant treatment group.

CONCLUSIONS

This study shows that lexipafant, the first PAF antagonist used in HIV-associated cognitive impairment, is a safe and well tolerated compound. The observed trends toward improvement in neuropsychological test scores warrant the pursuit of a larger and longer efficacy trial to assess the impact of lexipafant on cognitive performance.

Coreceptor ligand inhibition of fetal brain cell infection by HIV type 1

The capacity of a panel of HIV-1 isolates to infect primary mixed fetal brain cell cultures was estimated and their sensitivity to inhibition by a range of coreceptor ligands assessed. Our results show that (1) HIV-1 strains that predominantly use CCR5 or only CXCR4 are able to infect microglia in primary brain cell cultures, and (2) ligands to these two coreceptors can inhibit brain cell infection. CCR5 ligands (including AOP-RANTES, a potent inhibitor of CCR5-dependent infection), however, blocked infection only weakly, raising the possibility that alternative unidentified coreceptors are also used. Interestingly, vMIP-II, a chemokine encoded by the Kaposi sarcoma-associated herpes virus (KSHV), reduced brain cell infection by all HIV-1 strains tested, including both R5 and X4 viruses. Our results therefore indicate that novel drugs targeted to the major HIV-1 coreceptors will influence HIV replication in the brain, if they cross the blood-brain barrier.

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.

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.

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.

HIV-1 Tat induces neuronal death via tumor necrosis factor-alpha and activation of non-N-methyl-D-aspartate receptors by a NFkappaB-independent mechanism

Human immunodeficiency virus type 1 (HIV-1) infection of the central nervous system may result in neuronal apoptosis in vulnerable brain regions, including cerebral cortex and basal ganglia. The mechanisms for neuronal loss are likely to be multifactorial and indirect, since HIV-1 productively infects brain-resident macrophages and microglia but does not cause cytolytic infection of neurons in the central nervous system. HIV-1 infection of macrophages and microglia leads to production and release of diffusible factors that result in neuronal cell death, including the HIV-1 regulatory protein Tat. We demonstrate in this report that recombinant Tat1-86 and Tat peptides containing the basic region induce neuronal apoptosis in approximately 50% of vulnerable neurons in both rat and human neuronal cultures, and this apoptotic cell death is mediated by release of the pro-inflammatory cytokine tumor necrosis factor alpha, and by activation of glutamate receptors of the non-N-methyl-D-aspartate subtype. Finally, we show that Tat-induced apoptosis of human neuronal cell cultures occurs in the absence of activation of the transcription factor NFkappaB. These findings further define cellular pathways activated by Tat, that dysregulate production of tumor necrosis factor alpha, and lead to activation of glutamate receptors and neuronal death during HIV-1 infection of the central nervous system.

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

Human immunodeficiency virus type 1 (HIV-1) infection of the central nervous system results in neuronal apoptosis. Activated HIV-1-infected monocytes secrete high levels of the proinflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) and the phospholipid mediator platelet-activating factor (PAF). TNF-alpha and PAF are elevated in the central nervous system of patients with HIV-1-associated dementia. We now demonstrate that conditioned media from activated HIV-1-infected monocytes induces neuronal apoptosis, which can be prevented by co-incubation with PAF acetylhydrolase, the enzyme that catabolizes PAF in the central nervous system. Preceding apoptosis is a TNF-alpha-induced increase in neuronal ceramide levels. TNF-alpha-mediated neuronal apoptosis can also be blocked by co-incubation with PAF acetylhydrolase, or a PAF receptor antagonist. Blocking pathologic activation of PAF receptors may therefore be a pivotal step in the treatment of HIV-1-associated dementia.

Health care needs of medically underserved women of color: The role of the Bureau of Primary Health Care

The Bureau of Primary Health Care (BPHC) was developed to increase access to comprehensive primary and preventive health care and to improve the health status of medically underserved populations. Approximately 43 million Americans fall into this category, and the majority are poor, female, young, and uninsured. Under the Public Health Services Act, BPHC does not provide direct services, but rather assist local communities in identifying populations at risk of poor health outcomes and helps these communities through various programs. One of the newest initiatives of BPHC is the Office of Minority and Women's Health, developed with a mission to help reduce the disparities in the health status of women of racial and ethnic minority populations. This article outlines these disparities and discusses proposals for reducing them.

HIV neuropathogenesis and therapeutic strategies

Human immunodeficiency virus (HIV)-1 neuropathogenesis can be divided into three important components: (i) virus entry into the nervous system; (ii) the role of viral proteins and/or cellular products in neural tissue damage; (iii) the mechanisms of neuronal injury/death. Both blood derived macrophages or trafficking HIV-1 infected T-lymphocytes have been implicated in viral entry to the central nervous system (CNS). The major cell type harboring productive HIV-1 infection in the nervous system is the perivascular macrophage/microglia. The HIV-1 infection of brain astrocytes, restricted to the expression of regulatory gene products, may cause astrocyte dysfunction and contribute to neuronal injury or to disruption of the blood-brain barrier (BBB). Studies of cerebrospinal fluid and postmortem tissues reveal chronic inflammation/immune activation in the nervous system during the later stages of HIV-1 infection associated with disruption of BBB integrity. Blood-brain barrier damage may underlie the white matter pallor described in HIV-1 infection and could result in further entry into the CNS of toxic viral or cellular products, or additional HIV-1 infected cells. The HIV infected and activated macrophages/microglia produce excessive amounts of pro-inflammatory cytokines, including tumor necrosis factor alpha, and platelet activating factor. These products are directly toxic to human neurons in vitro. The HIV-1 envelope glycoprotein, gp 120 may stimulate the release of toxic factors from brain macrophages. Blocking N-methyl-D-aspartate (NMDA; or AMPA) glutamate receptors can antagonize candidate toxins of both viral and cellular origin. It has been postulated that (weak) excitotoxicity leads to oxidative stress in neurons and ultimately to apoptosis. Neuronal apoptosis occurs in the brains of both children and adults with HIV-1 infection. This understanding of HIV neuropathogenesis implies that therapeutic strategies should include: (i) anti-retroviral medications to decrease systemic and CNS virus load, and possibly to prevent perinatal transmission of HIV; (ii) anti-inflammatory compounds to decrease the chronic immune activation in microglia and allow the restoration of BBB integrity; and (iii) neuroprotective compounds to reduce neuronal injury and apoptotic death.

X-linked female band heterotopia-male lissencephaly syndrome

We report a family with band heterotopia in a mother and daughter and lissencephaly in a son (X-linked inheritance pattern). Postmortem examination of the boy revealed classical lissencephaly and, among other findings, simplified and discontinuous inferior olives without inferior olivary heterotopia. The absence of inferior olivary heterotopia may distinguish X-linked lissencephaly from other conditions with classic lissencephaly such as Miller-Dieker syndrome.

Persistence of human herpesvirus 6 according to site and variant: possible greater neurotropism of variant A

Little is known of the persistence and pathogenicity of human herpesvirus 6 (HHV-6) after primary infection, including the role of strain variant. Over 2 to 5 years, 2,716 children and 149 families were studied. Peripheral blood mononuclear cell (PBMC), saliva, and cerebrospinal fluid (CSF) specimens were examined for HHV-6 DNA and variant. Ninety-nine percent of isolates causing primary infection were HHV-6 variant B (HHV-6B), which predominated in 95%-98% of the variants persisting in PBMC and saliva specimens from children and adults. Of 668 CSF samples, 13% contained HHV-6 DNA; of 77 children examined after primary infection, 61% had HHV-6 DNA detected only in their CSF and 39% had HHV-6 DNA in both CSF and PBMCs. HHV-6 variant A (HHV-6A) was detected significantly (P = .0001) more frequently in CSF than in PBMCs or saliva. In children for whom HHV-6 was identified in both CSF and PBMCs, PBMCs contained only HHV-6B, while CSF contained HHV-6A or HHV-6B, not both. Thus, in patients with dual infection, only HHV-6A persisted in CSF, which suggests that HHV-6A has greater neurotropism. Findings for adults indicate that dual infection occurs; variant persistence is similar to that for children. The frequency of HHV-6A infection increased little with age, thereby indicating that HHV-6A infection remains uncommon into adulthood. This study suggests that HHV-6 variants have different immunobiologic courses and neurotropism.

Risk of recurrent seizures after a primary human herpesvirus 6-induced febrile seizure

OBJECTIVE

To test the hypothesis that children experiencing first febrile seizures caused by human herpesvirus 6 (HHV-6) have an increased risk for recurrent seizures when compared with children experiencing first febrile seizures attributed to other illnesses.

DESIGN AND PARTICIPANTS

Descriptive prospective study of 36 HHV-6 culture-positive children and a matched subgroup of 86 HHV-6 culture-negative children, all of whom had their first febrile seizures evaluated in a tertiary care emergency department and were followed for at least 12 months, with an average follow-up of 35.7 months.

PRIMARY OUTCOME MEASURE

The recurrence of seizures among HHV-6 culture-positive and HHV-6 culture-negative children with no known previous neurologic deficits.

RESULTS

A decreased incidence of recurrent seizures occurred in children whose first febrile seizures were caused by HHV-6. Twenty percent of HHV-6 culture-positive children and 40% of HHV-6 culture-negative children (P < 0.038) experienced a recurrent seizure within 1 year of their first febrile seizure. The mean time to recurrence within 12 months was 8.6 months for children with HHV-6 infection and 3.8 months (P < 0.001) for children without HHV-6 infection. Most recurrent seizures occurred within 12 months of a first febrile seizure for both HHV-6-positive and HHV-6-negative children (88 and 91%).

CONCLUSIONS

Children who had their first febrile seizures caused by primary HHV-6 infection did not demonstrate an increased risk for recurrent seizures when compared with children whose first febrile seizures were from other etiologies.

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.

Expression of pro- and anti-apoptosis gene products in brains from paediatric patients with HIV-1 encephalitis

We have previously demonstrated the presence of DNA fragmentation in neurons, macrophages and microglia consistent with apoptosis, but not in reactive astrocytes in brain tissue from paediatric patients with HIV-1 encephalitis (HIVE). To further understand the underlying mechanism(s) for these findings as they relate to gene-directed neural cell death, we studied the in-situ expression of the Bcl-2 family of proteins, including the pro-apoptosis gene product Bax, the anti-apoptosis gene product Bcl-2, and Bcl-x. We demonstrate significantly elevated numbers of Bax-positive microglia and macrophages immunoreactive in basal ganglia and cerebral cortex of children who had HIVE, in comparison to HIV-1 infected children without encephalitis or children who were seronegative for HIV-1. In contrast, patients with HIVE, but not HIV-1 without encephalitis, or seronegative controls, had increased expression of Bcl-2 and Bcl-x in reactive astrocytes in cortex and basal ganglia. In vitro studies using Western blot analysis demonstrated an up-regulation in the levels of Bax, and phosphorylated (i.e. inactive) Bcl-2 in HIV-1 infected macrophages, and in LPS-activated macrophages, relative to levels in virus-negative unstimulated macrophages. These results suggest that productive HIV-1 infection, or cellular activation, renders macrophages more vulnerable to apoptosis. Taken together, these findings suggest that brain-resident macrophages and microglia in patients with HIV-1 encephalitis are more prone to undergo apoptosis and that astrocytes in contrast may be resistant to apoptosis. This may represent a mechanism to limit microglial activation and the spread of productive HIV-1 infection in the CNS of children with HIV-1 encephalitis.

Human immunodeficiency virus type 1 Tat protein induces death by apoptosis in primary human neuron cultures

Neuronal loss in HIV encephalopathy remains a mystery since HIV-1 productively infects macrophage and microglia and only rarely infects neurons in the central nervous system. Apoptosis is a mechanism which may account for the loss of neurons in HIV-1 infected brain. Putative toxic factors that result in neuronal cell death in HIV-1 infection include the regulatory protein Tat, since this protein is known to be released from HIV-1 infected cells. Here we show that Tat induces cell death by apoptosis in cultured human fetal neurons producing characteristic morphological and biochemical features associated with apoptosis. These findings suggest that Tat may play an important role as a secreted, soluble neurotoxin in HIV-1 associated dementia.

Human fetal astrocytes as an ex vivo gene therapy vehicle for delivering biologically active nerve growth factor

The therapeutic use of neurotrophic factors for neurodegenerative diseases is promising, however, optimal methods for continuous delivery of these substances to the human central nervous system (CNS) remains problematic. One approach would be to graft genetically engineered human cells that continuously secrete high levels of a biologically produced and processed neurotrophic factor. This ex vivo gene therapy approach has worked well in animal models of neurodegenerative diseases using a variety of nonneuronal cell types to deliver the transgene. In our studies, we have been investigating the potential of astrocytes, a cell type normally present in the CNS, as a vehicle for ex vivo gene therapy. Here, we demonstrate that astrocytes in the human fetal cortex can be isolated and efficiently infected with an amphotropic retrovirus harboring mouse beta-nerve growth factor (NGF). These transduced astrocytes express high levels of NGF mRNA and secrete bioactive NGF protein as demonstrated by stimulation of neurite outgrowth from adrenal chromaffin cells. NGF ELISA showed that these astrocytes secrete NGF protein at a rate of 41 ng/day per 10(5) cells after 2 weeks in vitro, whereas NGF is undetectable in medium conditioned by normal astrocytes. These data suggest that human fetal astrocytes can be used for delivering biologically produced neurotrophic factors to the human CNS.

Tumor necrosis factor alpha inhibits glutamate uptake by primary human astrocytes. Implications for pathogenesis of HIV-1 dementia

Human immunodeficiency virus (HIV) infection is commonly associated with neurological disease that occurs in the apparent absence of extensive infection of brain cells by HIV, suggesting that indirect mechanisms account for neuropathogenesis in the CNS, perhaps including changes in the normal neuroprotective functions of astrocytes. To test this hypothesis, we examined the effect of the pro-inflammatory cytokine, tumor necrosis factor alpha (TNFalpha), produced by HIV-1-infected macrophages and microglia, on glutamate transport by primary human fetal astrocytes (PHFAs). A dose-dependent inhibition of high affinity glutamate uptake sites was observed 12-24 h after addition of exogenous recombinant human TNFalpha to PHFAs. This effect was specific since it was blocked by a neutralizing monoclonal antibody directed against TNFalpha. Furthermore, the inhibitory effect was reproduced by a monoclonal antibody that is an agonist at the 55-kDa TNF receptor. These results suggest that the neurotoxic effects of TNFalpha may be due in part to its ability to inhibit glutamate uptake by astrocytes, which in turn may result in excitotoxic concentrations of glutamate in synapses.

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.

Activation of nuclear factor kappa B in brains from children with HIV-1 encephalitis

Human immunodeficiency virus type 1 (HIV-1) infection of the central nervous system is associated with decreased neuronal density in discrete areas of the brain. Neuronal loss may occur via apoptosis, initiated by soluble neurotoxic factors secreted from HIV-1 infected macrophages and microglia. To examine further the molecular events involved in HIV-1 neuropathogenesis, we assessed the activity of NF kappa B, an inducible transcription factor involved in the activation of multiple proinflammatory, and potentially neurotoxic, genes. NF kappa B was analysed by immunocytochemistry using specific antisera to the NF kappa B p. 50 and p. 65 subunits. Brains from children with HIV-1 encephalitis and progressive encephalopathy were found to contain increased numbers of NF kappa B immunoreactive cells, relative to control brains (HIV-1 negative, or HIV-1 positive without encephalitis). Double-labelling studies using antibodies to CD68, or RCA-1 lectin, markers for cells of monocyte/macrophage lineage, revealed an increase in the number of microglia and macrophages with nuclear immunoreactivity for NF kappa B in association with HIV-1 encephalitis. NF kappa B positive multinucleated giant cells were also detected, as were cells which contained both NF kappa B and HIV-1 antigen. In contrast, the number of neurons and GFAP-positive astrocytes that were immunoreactive for NF kappa B was approximately the same in all groups of subjects. These data are consistent with the hypothesis that persistent, high-level activation of NF kappa B may promote the sustained production of neurotoxins by microglia and macrophages during HIV-1 encephalitis.

HIV-1 encephalopathy in children

HIV-1 infection is a worldwide pandemic, with an estimate of one to two million children infected by the end of the decade. The neurologic manifestations of primary HIV-1 infection in children are a major cause of morbidity and contribute to the fatal outcome in this condition. In the United States, HIV-1 is the most frequent cause of dementia in young adults. Because antiretroviral therapies and treatment for opportunistic infections have lengthened the survival time but not eradicated the virus from the central nervous system, it is likely that the incidence of neurologic dysfunction, including HIV-1 dementia, will increase. Available evidence suggests that the HIV-1 virus does not productively infect neurons but rather induces programmed cell death (apoptosis) in neurons by production of neurotoxic factors, including cytokines, phospholipid mediators, and eicosanoids, and HIV-1 gene products from HIV-1-infected macrophages in the brain. Understanding the mechanisms involved in neuronal cell injury and death may lead to new therapeutic interventions for the neurologic dysfunction associated with HIV-1 infection of the developing central nervous system.

The development of animal model systems for HIV-1 encephalitis and its associated dementia

The human immunodeficiency virus (HIV) is neuroinvasive and can be neurovirulent. Indeed, 20-30% of individuals with the acquired immune deficiency syndrome (AIDS) develop cognitive and motor dysfunction (termed the AIDS dementia complex or HIV dementia) coincident with advanced immunosuppression. Despite massive research efforts to discern viral neuropathogenic mechanisms, much remains incompletely understood. Recently, we and others developed animal model systems to elucidate how HIV infection within the brain can lead to impairment of central nervous system function. In this report, we evaluate each of the published animal models for their ability to mirror HIV dementia. Ease of handling and expense were also under consideration. Ultimately, studies in animal systems should permit a better understanding of the nature of HIV-1-induced neurological injury and aid in the development of effective treatments for this dreaded complication of HIV infection.

Apoptotic neurons in brains from paediatric patients with HIV-1 encephalitis and progressive encephalopathy

The pathogenesis of human immunodeficiency virus type 1 (HIV-1) associated dementia in adults involves neuronal loss from discrete areas of the neocortex and subcortical regions, but the mechanism for neuronal death is poorly understood. Gene-directed cell death resulting in apoptosis is thought to be a normal feature of neuronal development, but little is known about neuronal apoptosis in disease states. We investigated whether HIV-1 infection of the central nervous system is spatially associated with apoptosis of neurons. Using an in situ technique to identify newly cleaved 3'-OH ends of DNA as a marker for apoptosis, we demonstrate the presence of apoptotic neurons in cerebral cortex and basal ganglia of children that had HIV-1 encephalitis with progressive encephalopathy. Furthermore, an association was observed between the localization of apoptotic neurons and perivascular inflammatory cell infiltrates containing HIV-1 infected macrophages and multinucleated giant cells. Apoptotic neurons and p24-positive macrophages were observed infrequently in cerebral cortex and basal ganglia in children with HIV-1 infection without encephalitis or clinical encephalopathy. In nine control (HIV-1 negative) brains, ranging from the first post-natal month of life to 16.5 years of age, infrequent neuronal apoptosis was observed in three cases. These findings suggest that neuronal apoptosis is unlikely to be associated with post-natal development except in early post-natal germinal matrix, and that it may instead represent the end result of specific pathological processes, such as HIV-1 encephalitis.

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.

Cellular localization of human herpesvirus-6 in the brains of children with AIDS encephalopathy

Human herpesvirus-6, the etiologic agent of exanthem subitum, is a ubiquitous virus that infects almost all children by the age of 2 years and that has previously been shown to be neuroinvasive. These characteristics suggest that human herpesvirus-6 may be important in the neuropathogenesis of acquired immune deficiency syndrome (AIDS) in children. To address this hypothesis, we evaluated postmortem pediatric brain tissues for the presence of human herpesvirus-6 infection. Using in situ hybridization with a digoxigenin-labeled DNA probe for the large tegument protein gene of human herpesvirus-6, we detected nuclear signals in postmortem brain tissue from 4/5 children with human immunodeficiency virus-1 encephalitis. Human herpesvirus-6 DNA was found in numerous oligodendrocytes of the white matter and less frequently in astrocytes, macrophages, microglia and neurons. The human herpesvirus-6 positive cells detected by in situ hybridization were not immunoreactive either for human herpesvirus-6 early nuclear phosphoproteins or for surface glycoproteins associated with productive infection. Only rare human herpesvirus-6 infected cells were found in age-matched control brain tissues. No human herpesvirus-6 infected cells were found in human fetal brain tissue. These data suggest that human herpesvirus-6 is more extensively disseminated in neural cells in the presence of human immunodeficiency infection and immunodeficiency in pediatric AIDS patients, and it may contribute to the pathogenesis of AIDS encephalopathy.