Morphometric Comparisons of Optic Nerve Axon Loss in Acquired Immunodeficiency Syndrome

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.

Neuropathology of the retina in acquired immunodeficiency syndrome

The pathogenesis of HIV-mediated neurodegeneration is unknown. Presently, work is focused on two main hypotheses: direct (caused by HIV or component proteins) versus indirect (monocyte-mediated) neurotoxicity. In HIV-induced retinal disease, the high incidence of opportunistic infections and the low HIV viral burden found in most clinical specimens present challenges in defining the roles played by potential factors. Future studies will see the resolution of these controversies by showing the mechanism of HIV-induced neuronal damage and its relationship to retinal disease.

Dysfunction of visual pathways in HIV-1 infection

Foveal and conventional full field pattern-shift visual evoked potentials (f-VEPs and c-VEPs) were recorded bilaterally in 100 HIV seropositive homosexual men (HIVs) and in 40 age-matched healthy controls. In HIVs, both f-VEPs and c-VEPs revealed a significant mean increase in P100 latency (p < 0.001). In stage WR2 early conduction changes were detected in 17% of the stimulated eyes by f-VEPs and in 3% by c-VEPs. In patients with CD4 cell counts below 100/microliters a 33% reduction in the mean c-VEP amplitude was found (ANOVA p < 0.01). Multivariate analyses (MANCOVA) revealed that CD4 cell depletion was independently associated with lower (p < 0.01) and zidovudine treatment with higher c-VEP amplitudes (p < 0.05). Also patients with severe CD4 cell depletion showed a trend towards higher c-VEP amplitudes (p = 0.09) and lower f-VEP latencies (p = 0.08) after long lasting zidovudine treatment (Kruskal-Wallis test). Our data suggest that f-VEPs are a sensitive measure of subclinical optic fiber dysfunction in early HIV-1 infection and that axonal loss of optic fibers emerges with manifest immune deficiency. The inverse correlation of VEP changes and zidovudine treatment merits further studies on the question, whether inhibition of HIV replication may preserve visual pathway function.

Pattern of axonal loss in longstanding papilledema due to idiopathic intracranial hypertension

There is both clinical and histopathologic evidence for peripheral visual field loss and optic nerve degeneration in longstanding papilledema due to idiopathic intracranial hypertension (IIH). The purpose of this study was to look at the extent and distribution of axonal dropout in secondary optic atrophy due to IIH. Both optic nerves from a 29-year-old man with a two year history of IIH were examined histologically and morphometrically. A high-contrast lipid (myelin) stain, paraphenylenediamine (PPD), and a semiautomated image analysis system were employed to resolve sufficiently the optic nerve fiber images for counts and for measurement. There were 80% and 90% losses of axons, respectively, in the right and left optic nerves consequent to IIH. The axonal loss in the peripheral area of each optic nerve was much more severe than that in inner sectors (= 0.001 for the right optic nerve and = 0.005 for the left). This pattern of axonal dropout is consistent with the preservation of good central visual acuity despite devastating optic nerve atrophy, and with the severe peripheral visual field loss noted in this patient.

Deficits in perimetric performance in patients with symptomatic human immunodeficiency virus infection or acquired immunodeficiency syndrome

PURPOSE

We measured the perimetric performance in patients with either acquired immunodeficiency syndrome (AIDS) or human immunodeficiency virus (HIV) disease but without AIDS.

METHODS

Light-difference sensitivity in the central field was measured in 74 eyes of 37 patients. The Humphrey Field Analyzer 640, program 30-2 was used. Additionally, 143 eyes of 143 normal control subjects were studied.

RESULTS

Mean deviation was significantly reduced in patients with HIV disease compared with control subjects (mean +/- S.E.M., -4.30 +/- 0.52 vs -0.77 +/- 0.15, respectively; P < .0001). Analysis of subgroups demonstrated that patients with lymphadenopathy syndrome or AIDS-related complex (N = 40 eyes; -3.52 +/- 0.41; P < .0001) as well as patients with AIDS (N = 34 eyes; -5.23 +/- 0.97; P < .0001) had a reduced mean deviation. Those comparisons remained significant (P < .0001) when data were analyzed independently for the right eyes and for the left eyes. Corrected pattern standard deviation (3.15 +/- 0.30 vs 1.39 +/- 0.09; P < .0001) was higher in patients with HIV disease compared with control subjects. Again, analysis of subgroups disclosed a significant increase in patients with lymphadenopathy syndrome or AIDS-related complex (2.55 +/- 0.36; P < .0001) as well as in patients with AIDS (3.85 +/- 0.51; P < .0001). Both comparisons remained significant when data were analyzed independently for the right and left eyes.

CONCLUSIONS

This study demonstrates visual dysfunction despite normal visual acuity in patients with HIV disease. Our results are consistent with the hypothesis of damage at the neuroretinal level.

Optic nerve axon count and axon diameter in patients with ocular hypertension and normal visual fields

BACKGROUND

At postmortem examination, the authors obtained eight eyes of five individuals with elevated intraocular pressure and normal visual fields to study the axon count and mean axon diameter.

METHODS

Automated image analysis was used to calculate the total axon count and mean axon diameter per nerve and per nerve segment for each eye. The authors applied the method of identification analysis to compare each study eye with a corresponding normal eye of patients of the same age.

RESULTS

There was no statistically significant difference compared with control subjects for total axon count or segmental axon count for any of the eyes. Two eyes showed a statistically significant difference for mean axon diameter for the whole nerve but not for individual segments of the nerve.

CONCLUSIONS

Some eyes subjected to varying duration and magnitude of intraocular pressure elevation with normal visual fields may maintain normal axon counts and mean axon diameters.

AIDS-related dementia and calcium homeostasis

Approximately a third of adults and half of children with acquired immunodeficiency syndrome (AIDS) eventually suffer from neurological manifestations, including dysfunction of cognition, movement, and sensation. Among the various pathologies reported in the brain of patients with AIDS is neuronal injury and loss. A paradox arises, however, because neurons themselves are for all intents and purposes not infected by human immunodeficiency virus type 1 (HIV-1). This paper reviews evidence suggesting that at least part of the neuronal injury observed in the brain of AIDS patients is related to excessive influx of Ca2+. There is growing support for the existence of HIV- or immune-related toxins that lead indirectly to the injury or death of neurons via a potentially complex web of interactions between macrophages (or microglia), astrocytes, and neurons. Human immunodeficiency virus-infected monocytoid cells (macrophages, microglia, or monocytes), especially after interacting with astrocytes, secrete substances that potentially contribute to neurotoxicity. Not all of these substances are yet known, but they may include eicosanoids, that is, arachidonic acid and its metabolites, as well as platelet-activating factor. Macrophages activated by HIV-1 envelope protein gp120 also appear to release arachidonic acid and its metabolites. These factors can lead to increased glutamate release or decreased glutamate reuptake. In addition, gamma interferon (IFN-gamma) stimulation of macrophages induce release of the glutamate-like agonist quinolinate. Human immunodeficiency virus-infected or gp120-stimulated macrophages also produce cytokines, including tumor necrosis factor-alpha and interleukin-1 beta, which contribute to astrogliosis. A final common pathway for neuronal susceptibility appears to be operative, similar to that observed in stroke, trauma, epilepsy, neuropathic pain, and several neurodegenerative diseases, possibly including Huntington's disease, Parkinson's disease, and amyotrophic lateral sclerosis. This mechanism involves the activation of voltage-dependent Ca2+ channels and N-methyl-D-aspartate (NMDA) receptor-operated channels, and therefore offers hope for future pharmacological intervention. This review focuses on clinically tolerated calcium channel antagonists and NMDA antagonists with the potential for trials in humans with AIDS dementia in the near future.

Optic nerve morphometry following axonal degeneration from SAIDS in rhesus monkeys

In order to further study AIDS (acquired immunodeficiency syndrome) related neuropathologic findings, specifically progressive diffuse leuko-encephalopathy (PDL) and optic neuropathy, ten macaque monkeys (Macaca mulatta) were infected with simian immunodeficiency virus (SIV), observed for varying periods, and then sacrificed and tissue prepared for analysis. A marked difference from human AIDS pathology was found: in all monkeys, there was significant peripheral axonal dropout, as opposed to relatively little dropout in the central areas of the nerves (t stat. = -5.9, p < .001). In those monkeys infected with SIV for over one year, the axonal loss in the periphery was also greater than in the central optic nerve (t stat. = -5.03, p < .001); monkeys infected with SIV for less than one year had slightly less peripheral than central loss (t stat. = -4.5, p = .001). When compared with humans, however, it was found that the overall loss of axons was less (15% in monkeys vs. up to 45% in humans). There was also a lack of discernible retinal pathology, such as cotton wool spots, in the monkey tissue.

Platelet-activating factor: a candidate human immunodeficiency virus type 1-induced neurotoxin

The pathogenesis of central nervous system disease during human immunodeficiency virus type 1 (HIV-1) infection revolves around productive viral infection of brain macrophages and microglia. Neuronal losses in the cortex and subcortical gray matter accompany macrophage infection. The question of how viral infection of brain macrophages ultimately leads to central nervous system (CNS) pathology remains unanswered. Our previous work demonstrated high-level production of tumor necrosis factor alpha, interleukin 1 beta, arachidonic acid metabolites, and platelet-activating factor (PAF) from HIV-infected monocytes and astroglia (H. E. Gendelman, P. Genis, M. Jett, and H. S. L. M. Nottet, in E. Major, ed., Technical Advances in AIDS Research in the Nervous System, in press; P. Genis, M. Jett, E. W. Bernton, H. A. Gelbard, K. Dzenko, R. Keane, L. Resnick, D. J. Volsky, L. G. Epstein, and H. E. Gendelman, J. Exp. Med. 176:1703-1718, 1992). These factors, together, were neurotoxic. The relative role(s) of each of these candidate neurotoxins in HIV-1-related CNS dysfunction was not unraveled by these initial experiments. We now report that PAF is produced during HIV-1-infected monocyte-astroglia interactions. PAF was detected at high levels in CSF of HIV-1-infected patients with immunosuppression and signs of CNS dysfunction. The biologic significance of the results for neurological disease was determined by addition of PAF to cultures of primary human fetal cortical or rat postnatal retinal ganglion neurons. Here, PAF at concentrations of > or = 300 pg/ml produced neuronal death. The N-methyl-D-aspartate receptor antagonist MK-801 or memantine partially blocked the neurotoxic effects of PAF. The identification of PAF as an HIV-1-induced neurotoxin provides new insights into how HIV-1 causes neurological impairment and how it may ultimately be ameliorated.

HIV-related neuronal injury. Potential therapeutic intervention with calcium channel antagonists and NMDA antagonists

Perhaps as many as 25-50% of adult patients and children with acquired immunodeficiency syndrome (AIDS) eventually suffer from neurological manifestations, including dysfunction of cognition, movement, and sensation. How can human immunodeficiency virus type 1 (HIV-1) result in neuronal damage if neurons themselves are for all intents and purposes not infected by the virus? This article reviews a series of experiments leading to a hypothesis that accounts at least in part for the neurotoxicity observed in the brains of AIDS patients. There is growing support for the existence of HIV- or immune-related toxins that lead indirectly to the injury or demise of neurons via a potentially complex web of interactions among macrophages (or microglia), astrocytes, and neurons. HIV-infected monocytoid cells (macrophages, microglia, or monocytes), after interacting with astrocytes, secrete eicosanoids, i.e., arachidonic acid and its metabolites, including platelet-activating factor. Macrophages activated by HIV-1 envelope protein gp120 also appear to release arachidonic acid and its metabolites. In addition, interferon-gamma (IFN-gamma) stimulation of macrophages induces release of the glutamate-like agonist, quinolinate. Furthermore, HIV-infected macrophage production of cytokines, including TNF-alpha and IL1-beta, contributes to astrogliosis. A final common pathway for neuronal susceptibility appears to be operative, similar to that observed in stroke, trauma, epilepsy, neuropathic pain, and several neurodegenerative diseases, possibly including Huntington's disease, Parkinson's disease, and amyotrophic lateral sclerosis. This mechanism involves the activation of voltage-dependent Ca2+ channels and N-methyl-D-aspartate (NMDA) receptor-operated channels, and, therefore, offers hope for future pharmacological intervention. This article focuses on clinically tolerated calcium channel antagonists and NMDA antagonists with the potential for trials in humans with AIDS dementia in the near future.

Effects of the HIV-1 envelope glycoprotein gp120 in cerebellar cultures. [Ca2+]i increases in a glial cell subpopulation

The various types of cells present in cultures prepared from the postnatal rat cerebellum, identified by their gross morphology and immunocytochemistry, were loaded with the specific dye fura-2 and analysed individually for [Ca2+]i changes induced by the HIV-1 envelope glycoprotein gp120 and a variety of other treatments. In granule neurons [Ca2+]i increases were induced by high KCl and glutamate (mainly through the NMDA receptor) while in type-1 astrocytes this effect was observed after serotonin, carbachol and also quisqualate. In contrast, administration of gp120 was always without effect in these cells. Type-2 astrocytes (an arborized cell type responsive to agonists targeted to the glutamatergic AMPA and cholinergic receptors) were also most often unresponsive to the viral glycoprotein. However, among the cells exhibiting the arborized phenotype, a subpopulation (approximately 13%) responded to gp120 with conspicuous [Ca2+]i increases sustained by both release from intracellular stores and influx across the plasma membrane. These responses to the viral protein did not involve activation of either voltage-gated Ca2+ channels or glutamatergic receptors. Although not yet conclusively identified by specific cytochemical markers, the gp120-responsive cells resemble type-2 astrocytes and differ from neurons and type-1 astrocytes both in gross phenotype and in a number of receptor/channel properties: positivity to AMPA and cholinergic agonists; negativity to NMDA, serotonin and high KCl. From these results it is concluded that a subpopulation of glial cells is affected by gp120. The role of these cells in HIV brain infection and damage requires further studies to be precisely established.

Pupil cycle time and human immunodeficiency virus (HIV) infection

The pupil cycle time (PCT) was measured in 22 HIV-positive patients and 22 age/sex-matched controls. Of the HIV-positive group, 13 (59%) met the Centre for Disease Control classification of acquired immunodeficiency syndrome (AIDS) defining illness. There was a highly statistically significant difference in the PCT between the HIV-infected group and the control group (p < 0.0001, Student's t-test). Within the HIV-infected group there was no statistically significant difference in the PCT between those patients with full-blown AIDS and the others. This study suggests that HIV infection may be associated with subclinical ocular autonomic dysfunction even in the earlier stages of HIV infection.

Human immunodeficiency virus type 1 infection of the brain

Direct infection of the central nervous system by human immunodeficiency virus type 1 (HIV-1), the causative agent of AIDS, was not appreciated in the early years of the AIDS epidemic. Neurological complications associated with AIDS were largely attributed to opportunistic infections that arose as a result of the immunocompromised state of the patient and to depression. In 1985, several groups succeeded in isolating HIV-1 directly from brain tissue. Also that year, the viral genome was completely sequenced, and HIV-1 was found to belong to a neurotropic subfamily of retrovirus known as the Lentivirinae. These findings clearly indicated that direct HIV-1 infection of the central nervous system played a role in the development of AIDS-related neurological disease. This review summarizes the clinical manifestations of HIV-1 infection of the central nervous system and the related neuropathology, the tropism of HIV-1 for specific cell types both within and outside of the nervous system, the possible mechanisms by which HIV-1 damages the nervous system, and the current strategies for diagnosis and treatment of HIV-1-associated neuropathology.

Optic neuritis and HIV-1 infection

A patient is reported who developed acute optic neuritis in the context of severe immunodeficiency associated with HIV-1 infection. The clinical, laboratory, and radiological features are described and the possible associations with syphilis, multiple sclerosis, lymphoma, and HIV-1 infection are discussed.

Retinal disease associated with AIDS

In recent years an enormous amount of new information in the area of retinitis and retinal disease in immunosuppressed patients has been acquired. There have been exciting new developments in our understanding of the pathogenesis of retinal disease in AIDS patients as well as important advances in the diagnosis and therapy of infectious retinitis. This article will summarise the recent advances in this area and outline the direction of future research as it applies to the clinical management of patients with retinal manifestations of AIDS. Diagnostic and therapeutic difficulties will be addressed including the appropriate selection of antiviral drugs and other therapeutic modalities in patients with sight-threatening retinitis.