Human immunodeficiency virus type 1 infection of the brain

A 20-year population-based study of all-cause and cause-specific mortality among people with concurrent HIV and psychotic disorders

OBJECTIVE

We aimed to characterize mortality among people with HIV (PWH) and psychotic disorders (PWH/psychosis+) vs. PWH alone (PWH/psychosis-).

METHOD

A population-based analysis of mortality in PWH (age ≥19) in British Columbia (BC) from April 1996 to March 2017 was conducted using data from the Seek and Treat for Optimal Prevention of HIV/AIDS (STOP HIV/AIDS) study. Deaths were identified from the Vital Statistics Data (classified as HIV vs. non-HIV causes). Mortality trends across all fiscal years were examined. Cox models assessed the hazard of psychotic disorders on mortality; possible differences between schizophrenia and nonschizophrenia types of psychotic disorders were also evaluated.

RESULTS

Among 13 410 PWH included in the analysis, 1572 (11.7%) met the case definition for at least one psychotic disorder. Over the study period, 3274 deaths (PWH/psychosis-: n  = 2785, PWH/psychosis+: n  = 489) occurred. A decline over time in all-cause mortality and HIV-related mortality was observed in both PWH/psychosis+ and PWH/psychosis- ( P value <0.0001). A decline in non-HIV mortality was observed among PWH/psychosis- ( P value = 0.003), but not PWH/psychosis+ ( P value = 0.3). Nonschizophrenia psychotic disorders were associated with increased risk of mortality; adjusted hazard ratios with (95% confidence intervals): all-cause 1.75 (1.46-2.09), HIV-related 2.08 (1.60-2.69), non-HIV-related 1.45 (1.11-1.90). Similar associations between schizophrenia and mortality were not observed.

CONCLUSION

People with co-occurring HIV and nonschizophrenia psychotic disorders experienced a significantly higher risk of mortality vs. PWH without any psychotic disorder. Implementing care according to syndemic models considering interactions between HIV and particularly episodic psychotic disorders could help manage mortality risk more effectively among PWH/psychosis+.

Placental Macrophage (Hofbauer Cell) Responses to Infection During Pregnancy: A Systematic Scoping Review

BACKGROUND

Congenital infection of the fetus via trans-placental passage of pathogens can result in severe morbidity and mortality. Even without transmission to the fetus, infection of the placenta itself is associated with pregnancy complications including pregnancy loss and preterm birth. Placental macrophages, also termed Hofbauer cells (HBCs), are fetal-origin macrophages residing in the placenta that are likely involved in responding to placental infection and protection of the developing fetus. As HBCs are the only immune cell present in the villous placenta, they represent one of the final opportunities for control of infection and prevention of passage to the developing fetus.

OBJECTIVE AND RATIONALE

The objective of this review was to provide a systematic overview of the literature regarding HBC responses during infection in pregnancy, including responses to viral, bacterial, and parasitic pathogens.

METHODS

PubMed and Scopus were searched on May 20th, 2021, with no limit on publication date, to identify all papers that have studied placental macrophages/Hofbauer cells in the context of infection. The following search strategy was utilized: (hofbauer* OR "hofbauer cells" OR "hofbauer cell" OR "placental macrophage" OR "placental macrophages") AND [infect* OR virus OR viral OR bacteri* OR parasite* OR pathogen* OR LPS OR "poly(i:c)" OR toxoplasm* OR microb* OR HIV)].

OUTCOMES

86 studies were identified for review. This included those that investigated HBCs in placentas from pregnancies complicated by maternal infection and in vitro studies investigating HBC responses to pathogens or Pathogen-Associated Molecular Patterns (PAMPs). HBCs can be infected by a variety of pathogens, and HBC hyperplasia was a common observation. HBCs respond to pathogen infection and PAMPs by altering their transcriptional, translational and secretion profiles. Co-culture investigations demonstrate that they can replicate and transmit pathogens to other cells. In other cases, they may eliminate the pathogen through a variety of mechanisms including phagocytosis, cytokine-mediated pathogen elimination, release of macrophage extracellular traps and HBC-antibody-mediated neutralization. HBC responses differ across gestation and may be influenced by pre-existing immunity. Clinical information, including gestational age at infection, gestational age of the samples, mode of sample collection and pregnancy outcome were missing for the majority of studies.

Potential neuroinvasive and neurotrophic properties of SARS-CoV-2 in pediatric patients: comparison of SARS-CoV-2 with non-segmented RNA viruses

The emerging severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is causing global health crises. Children can be infected, but are less likely to develop severe neurological abnormalities compared with adults. However, whether SARS-CoV-2 can directly cause neurological impairments in pediatric patients is not known. The possible evolutionary and molecular relationship between SARS-CoV-2 and non-segmented RNA viruses were examined with reference to neurological disorders in pediatric patients. SARS-CoV-2 shares similar functional domains with neuroinvasive and neurotropic RNA viruses. The Spike 1 (S1) receptor binding domain and the cleavage sites at S1/S2 boundary are less conserved compared with the S2 among coronaviruses.

Acute HIV Infection Masquerading as Idiopathic Intracranial Hypertension: A Case Report and Literature Review

We describe a previously healthy 21-year-old man who presented acutely with signs and symptoms of raised intracranial pressure (ICP). Lumbar puncture yielded an elevated opening pressure and an acellular CSF analysis. Radiological images showed bilateral flattening of the posterior eye globes and an empty sella turcica. His serum HIV antigen/antibody was reactive. We provide a review of published cases that have been labeled as idiopathic intracranial hypertension (IIH) in HIV-infected patients, addressing the appropriateness of labeling such cases as truly idiopathic. We also discuss the importance of a thorough clinical evaluation of raised ICP in those who do not fulfil the typical IIH demographic.

HIV-1 Nef is released in extracellular vesicles derived from astrocytes: evidence for Nef-mediated neurotoxicity

Human immunodeficiency virus-associated neurological disorders (HANDs) affect the majority of AIDS patients and are a significant problem among HIV-1-infected individuals who live longer because of combined anti-retroviral therapies. HIV-1 utilizes a number of viral proteins and subsequent cytokine inductions to unleash its toxicity on neurons. Among HIV-1 viral proteins, Nef is a small protein expressed abundantly in astrocytes of HIV-1-infected brains and has been suggested to have a role in the pathogenesis of HAND. In order to explore its effect in the central nervous system, HIV-1 Nef was expressed in primary human fetal astrocytes (PHFAs) using an adenovirus. Our results revealed that HIV-1 Nef is released in extracellular vesicles (EVs) derived from PHFA cells expressing the protein. Interestingly, HIV-1 Nef release in EVs was enriched significantly when the cells were treated with autophagy activators perifosine, tomaxifen, MG-132, and autophagy inhibitors LY294002 and wortmannin suggesting a novel role of autophagy signaling in HIV-1 Nef release from astrocytes. Next, Nef-carrying EVs were purified from astrocyte cultures and neurotoxic effects on neurons were analyzed. We observed that HIV-1 Nef-containing EVs were readily taken up by neurons as demonstrated by immunocytochemistry and immunoblotting. Furthermore, treatment of neurons with Nef-carrying EVs induced oxidative stress as evidenced by a decrease in glutathione levels. To further investigate its neurotoxic effects, we expressed HIV-1 Nef in primary neurons by adenoviral transduction. Intracellular expression of HIV-1 Nef caused axonal and neurite degeneration of neurons. Furthermore, expression of HIV-1 Nef decreased the levels of phospho-tau while enhancing total tau in primary neurons. In addition, treatment of primary neurons with Nef-carrying EVs suppressed functional neuronal action potential assessed by multielectrode array studies. Collectively, these data suggested that HIV-1 Nef can be a formidable contributor to neurotoxicity along with other factors, which leads to HAND in HIV-1-infected AIDS patients.

Associations between HIV and schizophrenia and their effect on HIV treatment outcomes: a nationwide population-based cohort study in Denmark

BACKGROUND

Associations between HIV and schizophrenia in people with and without substance use disorders and the effect on timeliness of HIV diagnosis, antiretroviral therapy (ART), and treatment outcomes are poorly understood. We aimed to assess the association between HIV and schizophrenia and the effect on HIV treatment outcomes in people with and without substance use disorders.

METHODS

We did a population-based cohort study with data from nationwide registries in Denmark to investigate the risk of schizophrenia after a diagnosis of HIV and the risk of HIV after a diagnosis of schizophrenia, accounting for substance misuse, timeliness of HIV diagnosis, and treatment success in relation to schizophrenia. We selected the cohort from people born in Denmark between Jan 1, 1955, and Dec 31, 1995, who we followed up from their 16th birthday or Jan 1, 1995 (whichever occurred last) until their death, emigration from Denmark, onset of schizophrenia, or Dec 31, 2011 (whichever came first). We estimated incidence rate ratios (IRRs) with Poisson and Cox regression, with adjustment for calendar period, and age and its interaction with sex.

FINDINGS

We identified 2,786,286 individuals, of whom we included 2,646,154 people in analyses of risk of schizophrenia diagnosis and 2,658,662 people in analyses of risk of HIV diagnosis. In 35,353,633 person-years of follow up, HIV was associated with an increased risk of schizophrenia (IRR 4·09, 95% CI 2·73-5·83) and acute psychosis (7·15, 4·45-10·8); the IRR was highest within the first year of HIV diagnosis for both disorders (8·24, 2·95-17·7 and 12·7, 3·15-32·9, respectively). Schizophrenia was not associated with an increased risk of HIV in individuals without substance misuse disorders (IRR 1·42, 95% CI 0·81-2·27). The risk of schizophrenia in individuals with HIV decreased after ART (IRR 0·53, 0·32-0·87). The risk of acute psychosis did not differ between HIV-infected individuals receiving antiretroviral regimens with and without efavirenz (IRR 0·70, 95% CI 0·32-1·54). We recorded no differences in CD4 cell counts, time to ART, or viral suppression between individuals with schizophrenia with HIV and those without schizophrenia when substance use was taken into account. Between 1999 and 2011, the mortality rate ratio comparing HIV-infected individuals with schizophrenia with HIV-negative individuals without schizophrenia was 25·8 (95% CI 18·8-34·3).

INTERPRETATION

Our findings emphasise the need for interventions to prevent HIV in people with schizophrenia, especially for those with substance use disorders, and for accessible mental health services for individuals with HIV.

FUNDING

Stanley Medical Research Institute, Lundbeck Foundation, Preben and Anna Simonsen Fund, Novo Nordisk Foundation, The Danish AIDS Foundation, and the Augustinus Foundation.

Acute encephalitis as initial presentation of primary HIV infection

Acute encephalitis is a life-threatening condition. A wide variety of infectious agents are implicated and in many patients no cause is found. HIV acute seroconversion illness can rarely present as acute encephalitis. Although most experts agree in starting antiretroviral treatment in severe acute HIV infection, the evidence of the benefits are still lacking. The authors report a case of severe acute encephalitis as a primary presentation of HIV infection in which introduction of highly active antiretroviral treatment resulted in clinical recovery. This case highlights the need to consider HIV infection in the differential diagnosis of treatable viral encephalitis.

Loss of neuronal integrity during progressive HIV-1 infection of humanized mice

Neuronal damage induced by ongoing human immunodeficiency virus type 1 (HIV-1) infection was investigated in humanized NOD/scid-IL-2Rγ(c)(null) mice transplanted at birth with human CD34-positive hematopoietic stem cells. Mice infected at 5 months of age and followed for up to 15 weeks maintained significant plasma viral loads and showed reduced numbers of CD4(+) T-cells. Prospective serial proton magnetic resonance spectroscopy tests showed selective reductions in cortical N-acetyl aspartate in infected animals. Diffusion tensor imaging revealed structural changes in cortical gray matter. Postmortem immunofluorescence brain tissue examinations for neuronal and glial markers, captured by multispectral imaging microscopy and quantified by morphometric and fluorescence emission, showed regional reduction of neuronal soma and synaptic architectures. This was evidenced by loss of microtubule-associated protein 2, synaptophysin, and neurofilament antigens. This study is the first, to our knowledge, demonstrating lost neuronal integrity after HIV-1 infection in humanized mice. As such, the model permits studies of the relationships between ongoing viral replication and virus-associated neurodegeneration.

Acute meningoencephalitis due to human immunodeficiency virus type 1 infection in 13 patients: clinical description and follow-up

The objective of this study is to describe a series of cases of severe meningitis caused by human immunodeficiency virus type 1 (HIV-1) occurring during primary infection or after antiretroviral treatment interruption. In an observational cohort study, 13 patients with clinical diagnosis of meningitis or meningoencephalitis were reviewed. Ten cases occurred during primary HIV-1 infection and 3 after antiretroviral therapy (ART) withdrawal. Demographic parameters, clinical presentation and outcome, and laboratory and cerebrospinal fluid (CSF) parameters were recorded. The risk factor for HIV-1 infection acquisition was sexual transmission in all cases. The most frequent systemic symptoms were fever (12/13) and headeache (9/13). Among neurologic symptoms, focal signs appeared in seven patients (53.8%), confusion in six (46.2%), and agitation in five (38.5%). The median CD4 cell count was 434 cells/mm3. In all cases, CSF was a clear lymphocytaire fluid with normal glucose levels. Cranial computerized tomography was performed in seven patients, with a normal result in all of them; brain magnetic resonance in eight patients was normal in five cases and showing cortical atrophy, limbic encephalitis, and leptomeningeal enhancement in one patient each. The electroencephalographs (EEG) just showed diffuse dysfunction in three cases. ART was started in 11 patients. HIV RNA load at 12 months was <50 copies/ml in all treated patients. The 13 patients recovered without neurologic sequela. Meningitis or meningoencephalitis during primary HIV-1 infection or after ART cessation are unusual but sometimes a life-threatening manifestation. Although all patients tend to recover and the necessity of ART is not well established, some data suggest its potential benefit in these patients.

Oral Delivery of Pathogens from the Intestine to the Nervous System

Most therapeutic agents are delivered orally. Consequently, the major classes of therapeutically useful chemicals are partially lipophilic, small molecular weight compounds. They have reasonable permeability coefficient values across cell membranes, including those of intestinal epithelia and vascular endothelia. In contrast, large molecular weight biotechnology compounds have limited usefulness by non-injected routes as a consequence of their low membrane permeability and variable solubility. However, a wide range of infectious agents have developed strategies or have hijacked physiological routings in order to enter the host by the oral route. Efforts to address such issues have refreshed interest in mechanisms by which different types of payloads (including particulates and microorganisms) translocate across gut epithelia and then distribute to target tissues. Special attention is given to the potential role of the enteric nervous system and its plasticity.

Immune modulation by estrogens: role in CNS HIV-1 infection

Experimental and epidemiological data suggest that estrogen can be protective in both brain injury and infection. While estrogens can act directly on neurons to promote neuronal survival, estrogen also has antiinflammatory properties that may contribute to overall neuroprotection. Accordingly, estrogens may have particular relevance in chronic neuroimmune disorders such as HIV dementia. As AIDS is now a leading cause of death among women in their reproductive years, understanding the role that female sex hormones might play in the physiology of HIV-1 infection is especially critical. Indeed, there is accumulating evidence that many manifestations of HIV differ in women. For instance, it is now well established that women present with a lower viral titer at the time of seroconversion, have lower HIV viral loads compared to men at similar stages of disease, and may have altered disease progression during pregnancy. Conversely, while epidemiological studies suggest that women may be more vulnerable to certain late-stage AIDS-related illnesses including HIV dementia, there is accumulating data that strongly suggest an estrogen-deficient state is associated with long-term HIV infection in some women. Evaluated as a whole, existing evidence indicates that estrogen can directly protect neurons from damage, can modulate brain inflammation, and could act to maintain low titers of the HIV-1 virus. Accordingly, it can be hypothesized that maintenance of serum estradiol levels could decrease the incidence of HIV dementia and other AIDS-related neurological syndromes in HIV-1 positive women. In this article, we both summarize current understanding and present new data related to the potential mechanisms whereby estrogen could modulate the mechanics and the consequences of HIV-1 infection in the brain and thereby thwart the development of HIV dementia.

ATM deficiency induces oxidative stress and endoplasmic reticulum stress in astrocytes

ATM kinase, the product of the ataxia telangiectasia mutated (Atm) gene, is activated by genomic damage. ATM plays a crucial role in cell growth and development. Here we report that primary astrocytes isolated from ATM-deficient mice grow slowly, become senescent, and die in culture. However, before reaching senescence, these primary Atm(-/-) astrocytes, like Atm(-/-) lymphocytes, show increased spontaneous DNA synthesis. These astrocytes also show markers of oxidative stress and endoplasmic reticulum (ER) stress, including increased levels of heat shock proteins (HSP70 and GRP78), malondialdehyde adducts, Cu/Zn superoxide dismutase, procaspase 12 cleavage, and redox-sensitive phosphorylation of extracellular signal-regulated protein kinase 1 and 2 (ERK1/2). In addition, HSP70 and ERK1/2 phosphorylation are upregulated in the cerebella of ATM-deficient mice. This increase in ERK1/2 phosphorylation is seen primarily in cerebellar astrocytes, or Bergmann glia, near degenerating Purkinje cells. ERK1/2 activation and astrogliosis are also found in other parts of the brain, for example, the cortex. We conclude that ATM deficiency induces intrinsic growth defects, oxidative stress, ER stress, and ERKs activation in astrocytes.

No gender differences in the progression of nervous system disease in HIV infection

The past decade has seen a marked increase in the number of HIV-infected women in the United States. There has been recent concern that HIV disease in general may progress more rapidly in women than men, and some studies, primarily retrospective reviews, have suggested higher rates of neurologic disease among females. The objective of this study was to assess gender differences in HIV-related central and peripheral nervous system disease over time. Participants were enrolled in a longitudinal cohort study at the University of North Carolina and had annual follow-up evaluations. At baseline, 42 HIV-negative females, 52 HIV-positive females, and 52 HIV-positive males were compared for age, education, mode of infection, absolute CD4 cell count, and plasma/cerebrospinal fluid HIV RNA load. Subjects were evaluated by standardized clinical neurologic, neuropsychological, and laboratory examinations every year. The results indicated that both HIV-positive males and HIV-positive females had poorer neurologic functioning than the control group. However, there was no evidence from the parameters measured that the rate of decline differed between HIV-positive males and HIV-positive females.

The choroid plexus in the rise, fall and repair of the brain

The choroid plexuses (CPs) are involved in the most-basic aspects of neural function including maintaining the extracellular milieu of the brain by actively modulating chemical exchange between the CSF and brain parenchyma, surveying the chemical and immunological status of the brain, detoxifying the brain, secreting a nutritive "cocktail" of polypeptides and participating in repair processes following trauma. This diversity of functions may mean that even modest changes in the CP can have far-reaching effects. Indeed, changes in the anatomy and physiology of the CP have been linked to aging and several CNS diseases. It is also possible that replacing diseased or transplanting healthy CP might be useful for treating acute and chronic brain diseases. This review focuses on the wide-ranging and under-appreciated functions of the CP, alterations of these functions in aging and neurodegeneration, and recent demonstrations of the therapeutic potential of transplanted CP for neural trauma.

Possible involvement of both endoplasmic reticulum- and mitochondria-dependent pathways in MoMuLV-ts1-induced apoptosis in astrocytes

The Moloney murine leukemia virus (MoMuLV)-ts1 retrovirus, a naturally occurring mutant of MoMuLV-TB, causes a neuroimmunodegenerative syndrome in mice. The authors show here that ts1 triggers apoptosis in immortalized astrocytes, C1 cells, and primary cultured astrocytes, and that this apoptosis is caused by endoplasmic reticulum (ER) stress resulting from accumulation of the viral envelope preprotein gPr80(env). In ts1-infected C1 cells, an unfolded protein response was identified by activation of the ER-resident transmembrane protein kinase PERK, an event that leads to hyperphosphorylation of eIF2 alpha, up-regulation of GRP78, increased amounts of GADD153/CHOP, and cleavage of procaspase-12. Up-regulation of GRP78 and cleavage of procaspase-12 were also detected in primary cultured astrocytes infected with ts1. In ts1-infected C1 cells, ER stress was followed by mitochondrial stress, detected as mitochondrial transmembrane potential dissipation, cleavage of procaspase-9, and induction of activated caspase-3. In the brainstems of ts1-infected mice, activated caspase-3 and damaged mitochondria were identified in astrocytes within areas showing spongiform degeneration. Together the data imply that both ER stress- and mitochondrial stress-related apoptotic pathways are involved in ts1-induced astrocyte death.

Choroid plexus controls brain availability of anti-HIV nucleoside analogs via pharmacologically inhibitable organic anion transporters

OBJECTIVE

In AIDS, early suppression of the viral load in the central nervous system is critical for the efficacy of antiretroviral therapy, in order to prevent the emergence of a reservoir of resistant strains of virus, and brain impairment in late stages of the infection. The blood-cerebrospinal fluid (CSF) interface (i.e. the choroidal epithelium) constitutes the most direct route to reach the ventricular meningeal and perivascular infected macrophages, and may modulate the cerebral biodisposition of antiretroviral drugs through various transport systems. Our aim was to address nucleoside drug transfer specifically across the blood-CSF interface, and identify the possible mechanisms involved in their transport.

METHODS

Drug influx and efflux were measured using an in vitro cellular model that reproduces the barrier and transport properties of the blood-CSF interface in vivo. Transport mechanisms were investigated by competition studies.

RESULTS

The CSF influx rate of zidovudine was the highest, although moderate, followed by that of stavudine. The permeability coefficients of the other drugs tested were low. Zidovudine influx into the CSF is independent of thymidine transport systems, and more importantly is limited by an efflux mechanism. This efflux involves an apical (CSF-facing) carrier belonging to the solute carrier (Slc) 22 family of organic anion transporters, and can be inhibited by a therapeutic concentration of benzbromarone.

CONCLUSIONS

The demonstration and characterization of this efflux mechanism is the basis for the development of specific inhibitory agents in view to increase the delivery of antiretroviral nucleoside analogs to the brain.

A retrospective clinical, laboratory and outcome analysis in 43 cases of acute aseptic meningitis

Forty-three consecutive cases of acute aseptic meningitis (AAM) presenting within a 24-months period were retrospectively analysed with respect to clinical symptomatology, cerebrospinal fluid (CSF) findings, clinical course, treatment and outcome. Nineteen of the 43 AAM cases (44%) were caused by enterovirus, one by HIV (2%), two by Varicella zoster virus (5%), three due to herpes simplex virus I (7%), two due to herpes simplex virus II (5%), one due to Central European encephalitis virus (2%), and in 15 patients (35%) the aetiology of AAM remained unknown. Headache (100%) and fever (93%) were the presenting symptoms in the majority of cases. Signs of preceding infection were predominantly gastrointestinal in the enterovirus subgroup, but were inconsistently observed in the other subgroups. CSF findings at the first lumbar tap on admission generally revealed lymphomonocytic pleocytosis of less than 500 cells per micro l, mild to moderately elevated protein and normal lactate and glucose levels. Initial therapy consisted of an empirical antiviral and antibiotic regimen until a serological diagnosis was available. Acyclovir, effective only in herpes family viruses, was initially administered to all AAM cases. Effective therapy for other viral pathogens are not broadly available and treating AAM of unknown aetiology imposes a particular problem. The average hospitalization time ranged from 16 to 31 days. Patients were either discharged home (72%) or transferred to a rehabilitation centre (28%). The outcome was good (40%) to fair (51%) in the majority of cases.

Natural bovine lentiviral type 1 infection in Holstein dairy cattle. I. Clinical, serological, and pathological observations

Clinical, serological, and pathological abnormalities observed in Holstein cows naturally infected with bovine lentivirus 1 bovine immunodeficiency virus (BIV) and other infections were progressive and most commonly associated with weight loss, lymphoid system deficiency, and behavioral changes. Clinical evidence of meningoencephalitis was dullness, stupor, and occasional head or nose pressing postures. The polymerase chain reactions associated the BIV provirus with the lesions in the central nervous system and lymphoid tissues. Multiple concurrent infections developed in retrovirally infected cows undergoing normal stresses associated with parturition and lactation. A major functional correlate of the lymphoreticular alterations was the development of multiple secondary infections which failed to resolve after appropriate antibacterial therapy. The chronic disease syndrome in dairy cows associated with BIV may be useful as a model system for investigation of the pathogenesis of the nervous system lesions and lymphoid organ changes that occur in humans with lentiviral infection.

Low prevalence of TT virus in the cerebrospinal fluid of viremic patients with central nervous system disorders

TT virus (TTV) is a widespread infectious agent of humans identified in 1998. In infected individuals, TTV induces persistent viremia but its life cycle and pathogenic potential are still poorly understood. In the present study, the presence of TTV DNA in 32 consecutive paired serum and cerebrospinal fluid (CSF) samples from patients with neurological (mainly multiple sclerosis) disorders was investigated by means of a sensitive quantitative real-time PCR assay. Of the 24 patients who were found to carry TTV DNA in serum, 3 also had detectable TTV DNA in their CSF. Two TTV positive CSF samples had markers indicative of blood contamination or a disrupted blood-brain barrier and contained considerably lower TTV loads as compared with the corresponding serum samples, thus suggesting that the virus they contained was of plasma origin. These findings indicated that in general TTV does not permeate effectively an intact blood-brain barrier. Furthermore, the CNS does not represent a common site of TTV replication and persistence. However, at least one exception was observed: the third TTV positive CSF sample (obtained from a patient with subacute dementia of unknown origin) showed no markers suggestive of disrupted blood-brain barrier or blood contamination and had a TTV DNA concentration similar to that found in the patient's serum. In addition, the TTV isolates detected in the two body fluids were distinct genetically. The detection of TTV DNA in CSF is of considerable interest but the clinical significance remains unknown.

HIV type 1 infection of human astrocytes is restricted by inefficient viral entry

The mechanism by which HIV infects astrocytes is not known. We used the simian virus 40 (SV40)-transformed human astrocyte cell line, SVG-A, to investigate HIV infection of astrocytes. We previously reported that SVG-A cells are susceptible to low levels of CD4/CXCR4-independent infection by an X4 strain of HIV-1. Infection was greatly increased when the prototypical X4 receptors, CD4 and CXCR4, were expressed on the SVG-A cells (SVGCD4-X4). These data suggest that HIV-1 enters astrocytes by a novel mechanism that is inefficient compared with CD4/CXCR4-mediated entry. In this article, we report high levels of early viral gene expression in both SVG-A and SVGCD4-X4 cells once the HIV entry pathway is circumvented. These data indicate that HIV-1 infection of SVG-A cells is restricted by inefficient viral entry rather than by post-entry events. As we were unable to detect infection of nontransformed primary astrocytes, we investigated whether SV40 transformation affects the susceptibility of astrocytes to HIV infection. To study this, we transformed primary fetal and adult astrocytes with the same origin-defective SV40 mutant that was used to transform the SVG-A cell line. We found that SV40 transformation did not alter the susceptibility of astrocytes to HIV infection. Furthermore, high levels of early viral gene expression were detected in these cells once the HIV entry process was by-passed. Taken together, the results of these studies indicate that HIV infection of human astrocytes is restricted by inefficient viral entry.

Role of CD23 in astrocytes inflammatory reaction during HIV-1 related encephalitis

Soluble factors released by intra-cerebral activated cells are implicated in neuronal alterations during central nervous system inflammatory diseases. In this study, the role of the CD23 pathway in astrocyte activation and its participation in human immunodeficiency virus-1 (HIV-1)-induced neuropathology were evaluated. In human primary astrocytes, CD23 protein membrane expression was dose-dependently upregulated by gp120. It was also upregulated by gamma-interferon (gamma-IFN) and modulated by interleukin-1-beta (IL-1beta) whereas microglial cells in these stimulation conditions did not express CD23. Cell surface stimulation of CD23 expressed by astrocytes induced production of nitric oxide (NO) and IL-1beta which was inhibited by a specific inducible NO-synthase (iNOS) inhibitor (aminoguanidine), indicating the implication of this receptor in the astrocyte inflammatory reaction. On brain tissues from five out of five patients with HIV-1-related encephalitis, CD23 was expressed by astrocytes and by some microglial cells, whereas it was not detectable on brain tissue from five of five HIV-1-infected patients without central nervous system (CNS) disease or from two of two control subjects. In addition, CD23 antigen was co-localized with iNOS and nitrotyrosine on brain tissue from patients with HIV1-related encephalitis, suggesting that CD23 participates in iNOS activation of astrocytes in vivo. In conclusion, CD23 ligation is an alternative pathway in the induction of inflammatory product synthesis by astrocytes and participates in CNS inflammation.

Virus receptors in the human central nervous system

The initial event in the life cycle of a virus is its interaction with receptors present on the surface of a cell. Understanding these interactions is important to our understanding of viral tropism, spread, and pathogenesis. This is particularly true of viruses that target the central nervous system as these viruses must maintain a tropism for both the nervous system and for peripheral organs that allow for viral replication and spread to new susceptible hosts. These viruses therefore interact with a diverse set of cells and tissues, interactions that are likely mediated by both common and unique receptors present on each target tissue. In addition, physiological changes in the host can lead to increased or decreased expression of virus receptors, which influence virus trafficking, spread, and tissue specific pathology. This review will focus on the relatively few virus receptor systems that have been described in some level of detail for viruses that target the human central nervous system.

Retroviral RNA identified in the cerebrospinal fluids and brains of individuals with schizophrenia

Schizophrenia is a serious brain disease of uncertain etiology. A role for retroviruses in the etiopathogenesis of some cases of schizophrenia has been postulated on the basis of clinical and epidemiological observations. We found sequences homologous to retroviral pol genes in the cell-free cerebrospinal fluids (CSFs) of 10 of 35 (29%) individuals with recent-onset schizophrenia or schizoaffective disorder. Retroviral sequences also were identified in the CSFs of 1 of 20 individuals with chronic schizophrenia. However, retroviral sequences were not identified in any of the CSFs obtained from 22 individuals with noninflammatory neurological diseases or from 30 individuals without evidence of neurological or psychiatric diseases (chi(2) = 19.25, P < 0.001). The nucleotide sequences identified in the CSFs of the individuals with schizophrenia or schizoaffective disorder were related to those of the human endogenous retroviral (HERV)-W family of endogenous retroviruses and to other retroviruses in the murine leukemia virus genus. Transcription of RNA homologous to members of the HERV-W family of retroviruses also was found to be up-regulated differentially in the frontal cortex regions of brains obtained postmortem from individuals with schizophrenia, as compared with corresponding tissue from individuals without psychiatric diseases. The transcriptional activation of certain retroviral elements within the central nervous system may be associated with the development of schizophrenia in at least some individuals. The further characterization of retroviral elements within the central nervous system of individuals with schizophrenia might lead to improved methods for the diagnosis and management of this disorder.

Synthesis and antiviral evaluation of C-4-hydrazide derivatives of 2',3'-dideoxycytidine

Syntheses of three hitherto unknown derivatives of 2',3'-dideoxycytidine, namely C-4-(salicylic hydrazide)-ddC, C-4-(N-butyloxycarbonyl-isoleucine hydrazide)-ddC and its N-unprotected chlorhydrate salt have been carried out. These compounds do not induce inhibition of HIV-1 replication in cell culture experiments. Nevertheless, the modifications on the base moiety increased in all cases the lipophilicity of the parent molecule with an acceptable water solubility compared to ddC.

CD4/CXCR4-independent infection of human astrocytes by a T-tropic strain of HIV-1

HIV-1 establishes a low-level persistent infection in astrocytes. In this study, we studied the susceptibility of a human astrocyte cell line (SVG-A) to infection with luciferase expressing reporter viruses pseudotyped with envelopes derived from five isolates of HIV-1. SVG-A cells were susceptible to infection by a T-cell tropic isolate and the infection was both CD4 and CXCR4 independent. These data confirm the susceptibility of astrocytes to infection with T-tropic strains of HIV-1 and suggest a novel mechanism by which T-tropic strains of HIV can infect cells.

Varied tropism of HIV-1 isolates derived from different regions of adult brain cortex discriminate between patients with and without AIDS dementia complex (ADC): evidence for neurotropic HIV variants

A number of infected individuals develop neuropathological disorders, such as AIDS dementia complex (ADC), as a consequence of HIV/AIDS. The biological features governing HIV entry and tropism in different brain cell types remain unclear, as do the genetics of the virus regulating these events and the neuropathogenic processes within the brain tissues. HIV-1 was isolated from the right and left parietal, occipital, and frontal lobes of the brain cortex of three HIV-1-infected patients: two with ADC and one without. The viral strains were studied from the innate tissues and various primary cell cultures. The kinetics and tropism of viral strains from different brain regions showed clear differences on various primary cell types (monocytes, monocyte-derived macrophages, and T cells), which could discriminate between biological behavior of HIV-1 strains from patients with and without ADC. The variable effect of different donor cells on tropism was also clearly evident. The majority (with a few exceptions) of isolates from different brain regions of all three patients used CCR5 as coreceptor for entry. The consistent CCR5 use, macrophage tropism, and non-syncytium-inducing phenotype were the main characteristics of the brain-derived HIV-1 strains from all three patients. Importantly, viral strains derived directly from innate brain tissue of the patient without ADC showed some differences from the cultured variants of the same patient, whereas those from brain tissue of the patients with ADC were more similar to the culture-adapted strains. This suggests that the emergence of primary cell type-adapted isolates during ADC may play a crucial role in the development and progression of the neuropathology associated with ADC. The different genotypes residing in different areas of brain combined with their differential tropism and coreceptor use suggest that neurotropic variants exist that may be governing the neurological manifestation of HIV disease in infected patients.

HIV type 1 nef gene inhibits tumor necrosis factor alpha-induced apoptosis and promotes cell proliferation through the action of MAPK and JNK in human glial cells

In neurodegenerative diseases associated with AIDS, reactive astrocytosis plays a central role in the neurotoxicity of the brain parenchyma. Whereas the HIV-1 nef gene is overexpressed during restricted HIV-1 infection of human astrocytes, our previous results have demonstrated that nef expressed in human U251MG glial cells activates the sphingomyelin pathway triggered by TNF-alpha, increasing ceramide production. Since ceramide is an important regulatory molecule of programmed cell death induced by TNF-alpha, we examined whether nef could alter TNF-alpha-induced apoptosis in the U251MG human astrocytoma cell line. Transfection studies indicated that nef could both prevent apoptosis and promote cell proliferation in response to TNF-alpha stimulation. MAPK and JNK activities were further analyzed in order to elucidate signaling cascades subsequent to the upregulation of ceramide production. After TNF-alpha treatment, both kinases were shown to be preferentially activated in the presence of nef. These experiments strongly suggest that the HIV-1 Nef protein might modulate the sensitivity of astrocytes to inflammatory molecules, thus contributing to the development of neurodegenerative diseases associated with AIDS.

Intracerebral aneurysms in human immunodeficiency virus infection: case report and literature review

We describe a child with human immunodeficiency virus infection who presented with a large subarachnoid hemorrhage. She had multiple saccular and fusiform aneurysms in the proximal cerebral arterial circulation and no evidence of bacterial or fungal infection. The arteriopathy coincided with a high human immunodeficiency virus RNA load. Human immunodeficiency virus may cause cerebral arteriopathy with potentially life-threatening complications.

Choroid plexus in the central nervous system: biology and physiopathology

Choroid plexuses (CPs) are localized in the ventricular system of the brain and form one of the interfaces between the blood and the central nervous system (CNS). They are composed of a tight epithelium responsible for cerebrospinal fluid secretion, which encloses a loose connective core containing permeable capillaries and cells of the lymphoid lineage. In accordance with its peculiar localization between 2 circulating fluid compartments, the CP epithelium is involved in numerous exchange processes that either supply the brain with nutrients and hormones, or clear deleterious compounds and metabolites from the brain. Choroid plexuses also participate in neurohumoral brain modulation and neuroimmune interactions, thereby contributing greatly in maintaining brain homeostasis. Besides these physiological functions, the implication of choroid plexuses in pathological processes is increasingly documented. In this review, we focus on some of the novel aspects of CP functions in relation to brain development, transfer of neuro-humoral information, brain/immune system interactions, brain aging, and cerebral pharmaco-toxicology.

Diminished rev-mediated stimulation of human immunodeficiency virus type 1 protein synthesis is a hallmark of human astrocytes

Astrocytes are target cells for human immunodeficiency virus type 1 (HIV-1) in the central nervous system with attenuated virus replication in vivo and in vitro. In infected astrocytes, viral gene expression is restricted mainly to nonstructural (early) viral components like Nef, suggesting inhibition of Rev-dependent posttranscriptional processes in these cells. Because of the heterogeneity of astrocytic cells, the objective of this study was to determine whether restriction of HIV-1 Rev-associated activities is a common property of human astrocytes. To this end, we compared the trans activation capacity and intracellular distribution of Rev in four astrocytoma cell lines previously shown to be infectible by HIV-1 and in primary human fetal astrocytes from different sources with Rev-permissive nonglial control cell lines. In all astrocytic cell cultures, the Rev response was reduced to about 10% of that of Rev-permissive control cells. Rev was apparent both in cytoplasmic and in nuclear compartments of living astrocytes, in contrast to the typical nuclear and/or nucleolar localization of Rev in permissive control cells. Nuclear accumulation of Rev in astrocytes was restored by blocking export of Rev. The trans activation capacity and nuclear localization of Tat were not affected in astrocytes. These results demonstrate that inhibition of Rev-dependent posttranscriptional regulation of HIV-1 is a hallmark of human astrocytes and may contribute to suppression of HIV-1 production in these HIV-1 reservoirs. Astrocytes constitute the first example of a human cell type showing an impaired Rev response, indicating that posttranscriptional control of HIV-1 gene expression can be modulated in a cell-dependent manner.

Changes in and discrepancies between cell tropisms and coreceptor uses of human immunodeficiency virus type 1 induced by single point mutations at the V3 tip of the env protein

We examined the effect of amino acid substitutions of the GPGR (glycine-proline-glycine-arginine) tip sequence at the V3 domain of the Env protein of human immunodeficiency virus type 1 (HIV-1) on its cell tropism and coreceptor use. We changed the GPGR sequence of a T-cell line (T)- and macrophage (M)-tropic (R5-R3-X4) HIV-1 strain, GUN-1wt, to GA(alanine)GR (the resulting mutant was designated GUN-1/A), GL(leucine)GR (GUN-1/L), GP(proline)GR (GUN-1/P), GR(arginine)GR (GUN-1/R), GS(serine)GR (GUN-1/S), or GT(threonine)GR (GUN-1/T). GUN-1/A, GUN-1/S, and GUN-1/T mutants infected brain-derived cells such as a CD4-transduced glioma cell line, U87/CD4, and a brain-derived primary cell strain, BT-20/N, as well as T-cell lines in a CD4-dependent manner, although the plating of these mutants onto macrophages was inhibited. GUN-1/L, GUN-1/P, and GUN-1/R mutants showed both T- and M-tropism, but did not plate onto the brain-derived cells. A CCR3, CCR5, CCR8, or CXCR4 gene was introduced into a CD4-positive glioma cell line, NP-2/CD4, which demonstrated complete resistance to various HIV-1 strains. Not only HIV-1 strains, which were infectious to macrophages, such as GUN-1wt, GUN-1v, GUN-1/L, and GUN-1/P, but also an HIV-1 strain, GUN-1v, which was hardly infectious to macrophages, grew well in NP-2/CD4 cells expressing CCR3 or CCR5. However, the M-tropic GUN-1/R mutant could not efficiently use CCR5 nor CCR3. No point mutants, except GUN-1/L, grew well in NP-2/CD4 cells expressing CCR8. These findings indicate that the cell tropism of HIV-1 to macrophages and brain-derived cells and their use of the coreceptors were markedly, though not always concomitantly, affected by the tip sequence of the V3 domain.

Inflammatory Cytokines and HIV-1-Associated Neurodegeneration: Oncostatin-M Produced by Mononuclear Cells from HIV-1-Infected Individuals Induces Apoptosis of Primary Neurons

Neurologic abnormalities are common in HIV-1-infected patients and often represent the dominant clinical manifestation of pediatric AIDS. The neurological dysfunction has been directly related to CNS invasion by HIV-1 that is principally, if not exclusively, supported by blood-derived monocytes/macrophages and lymphocytes. By using primary long term cultures of human fetal sensory neurons as well as sympathetic precursors-like neuronal cells, we determined that blood-derived mononuclear cells from HIV-1-infected individuals spontaneously release soluble mediators that can potently inhibit the growth and survival of developing neurons as well as the viability of postmitotic neuronal cells by inducing apoptotic cell death. Analysis of the cytokines produced by lymphomonocytic cells, HIV-1 infected or activated, indicated that oncostatin M (oncM) is a major mediator of these effects. Since low TGF-β1 concentrations were capable of enhancing oncM-mediated neuronal alterations, our data indicate that by acting in concert with other cytokines, oncM may induce neuronal demise in both the developing and the mature brain. Thus, this cytokine may contribute to the setting of the neuronal cell damage observed in HIV-1-infected individuals.

Human astrocytes inhibit HIV-1 expression in monocyte-derived macrophages by secreted factors

OBJECTIVE

To determine the effects of primary human fetal and adult astrocytes on HIV-1 replication in monocyte-derived macrophages (MDM).

DESIGN

HIV-1 can infect the brain in the early stage of systemic infection. The HIV-1-associated cognitive/motor complex develops later in the course of the disease, suggesting that brain cells may inhibit the early productive infection and the development of neurological disease. In this study, we established an in-vitro coculture system to determine whether astrocytes can modulate HIV-1 replication in MDM.

METHODS

Elutriated human monocytes were differentiated in culture, then infected with monocyte tropic HIV-1. One day after infection, MDM were co-cultured with primary astrocytes. Reverse transcriptase (RT) activity was used to monitor virus replication. RT-polymerase chain reaction (PCR), enzyme-linked immunosorbent assay (ELISA) and bioassay were used to assess cytokine production.

RESULTS

Primary human astrocytes suppressed HIV-1 replication in MDM via the production of soluble factors. Cytokine inhibitors of HIV-1, such as IFN-gamma, IL-4, IL-10 and IL-13, were not detectable, whereas transforming growth factor beta (TGF-beta) was constitutively produced only in its latent form. Paraformaldehyde-fixed astrocytes, unable to secrete cytokines, failed to inhibit HIV-1. These cells caused enhanced virus replication, however, which correlated with an increase in macrophage colony stimulating factor (M-CSF) production.

CONCLUSIONS

Human astrocytes can increase and decrease HIV-1 expression in MDM. An imbalance between the positive and negative effects of astrocytes may contribute to the expression of virus in the brain, and the development of HIV-1-associated cognitive/motor complex.

Human Immunodeficiency Virus-1–Infected Macrophages Induce Inducible Nitric Oxide Synthase and Nitric Oxide (NO) Production in Astrocytes: Astrocytic NO as a Possible Mediator of Neural Damage in Acquired Immunodeficiency Syndrome

Nitric oxide (NO) plays an important role in normal neural cell function. Dysregulated or overexpression of NO contributes to neurologic damage associated with various pathologies, including human immunodeficiency virus (HIV)-associated neurological disease. Previous studies suggest that HIV-infected monocyte-derived macrophages (MDM) produce low levels of NO in vitro and that inducible nitric oxide synthase (iNOS) is expressed in the brain of patients with neurologic disease. However, the levels of NO could not account for the degree of neural toxicity observed. In this study, we found that induction of iNOS with concomitant production of NO occurred in primary human astrocytes, but not in MDM, when astrocytes were cocultured with HIV-1–infected MDM. This coincided with decreased HIV replication in infected MDM. Supernatants from cocultures of infected MDM and astrocytes also stimulated iNOS/NO expression in astrocytes, but cytokines known to induce iNOS expression (interferon-γ, interleukin-1β, and tumor necrosis factor-) were not detected. In addition, the recombinant HIV-1 envelope protein gp41, but not rgp120, induced iNOS in cocultures of uninfected MDM and astrocytes. This suggests that astrocytes may be an important source of NO production due to dysregulated iNOS expression and may constitute one arm of the host response resulting in suppression of HIV-1 replication in the brain. It also leads us to speculate that neurologic damage observed in HIV disease may ensue from prolonged, high level production of NO.

The role of excitotoxicity in neurodegenerative disease: implications for therapy

Glutamic acid is the principal excitatory neurotransmitter in the mammalian central nervous system. Glutamic acid binds to a variety of excitatory amino acid receptors, which are ligand-gated ion channels. It is activation of these receptors that leads to depolarisation and neuronal excitation. In normal synaptic functioning, activation of excitatory amino acid receptors is transitory. However, if, for any reason, receptor activation becomes excessive or prolonged, the target neurones become damaged and eventually die. This process of neuronal death is called excitotoxicity and appears to involve sustained elevations of intracellular calcium levels. Impairment of neuronal energy metabolism may sensitise neurones to excitotoxic cell death. The principle of excitotoxicity has been well-established experimentally, both in in vitro systems and in vivo, following administration of excitatory amino acids into the nervous system. A role for excitotoxicity in the aetiology or progression of several human neurodegenerative diseases has been proposed, which has stimulated much research recently. This has led to the hope that compounds that interfere with glutamatergic neurotransmission may be of clinical benefit in treating such diseases. However, except in the case of a few very rare conditions, direct evidence for a pathogenic role for excitotoxicity in neurological disease is missing. Much attention has been directed at obtaining evidence for a role for excitotoxicity in the neurological sequelae of stroke, and there now seems to be little doubt that such a process is indeed a determining factor in the extent of the lesions observed. Several clinical trials have evaluated the potential of antiglutamate drugs to improve outcome following acute ischaemic stroke, but to date, the results of these have been disappointing. In amyotrophic lateral sclerosis, neurolathyrism, and human immunodeficiency virus dementia complex, several lines of circumstantial evidence suggest that excitotoxicity may contribute to the pathogenic process. An antiglutamate drug, riluzole, recently has been shown to provide some therapeutic benefit in the treatment of amyotrophic lateral sclerosis. Parkinson's disease and Huntington's disease are examples of neurodegenerative diseases where mitochondrial dysfunction may sensitise specific populations of neurones to excitotoxicity from synaptic glutamic acid. The first clinical trials aimed at providing neuroprotection with antiglutamate drugs are currently in progress for these two diseases.

Drug delivery of antisense molecules to the brain for treatment of Alzheimer's disease and cerebral AIDS

Antisense oligonucleotides (ODNs) and peptide nucleic acids (PNAs) are potential therapeutics for eradication of malignancies, viral infections, and other pathologies. However, ODNs and PNAs in general are unable to cross cellular membranes and blood-tissue barriers, such as the blood-brain barrier (BBB), which is only permeable to lipophilic molecules of molecular weight <600 Da. Cellular delivery systems based on conjugates of streptavidin (SA) and the OX26 monoclonal antibody directed to the transferrin receptor may be employed as a universal carrier for the transport of mono-biotinylated peptides, ODNs, or PNAs. 3'-Biotinylation of phosphodiester (PO)-ODN produces complete protection of ODN against serum and cellular 3'-exonucleases, facilitating the conjugation to avidin-based delivery systems and maintaining the activation of RNase H. These delivery systems markedly increased the cellular uptake and antisense efficacy of 3'-biotinylated ODNs in models of Alzheimer's disease and HIV-AIDS. In vivo brain delivery studies demonstrated that 3'-protected PO-ODNs and PO-phosphorothioate(PS)-ODN hybrids containing a single PO linkage are subjected to endonuclease degradation in vivo. On the contrary PS-ODNs, which were also protected at 3'-terminus by biotinylation, are metabolically stable in vivo and resistant to exo/endonuclease degradation. However, because of the strong binding of these oligomers to plasma protein, PS-ODNs are poorly transported into the brain through the BBB by the OX26-SA delivery vector following intravenous administration. PNAs are also resistant to exo/endonuclease and protease degradation, and these molecules biotinylated at the amino terminal group were transported into the brain by the OX26-SA delivery system with brain uptake levels comparable to that of morphine. Using the rev gene of HIV as a model target, RNase protection assays and cell-free translation arrest showed that the PNA-OX26-SA conjugate maintained active recognition and inactivation of target mRNA, respectively. The overall experimental evidence suggests that PNA-OX26-SA conjugates represent optimal antisense molecules for drug delivery to the brain.

Encephalopathy and cytomegalovirus colitis in an AIDS child

A 2-year-old girl, who had prolonged thrush and spastic diplegia, was found to have a mother-to-child vertical transmission of human immunodeficiency virus type-1 (HIV). A brain computed tomography scan revealed a symmetrical calcification on the bilateral basal ganglia and periventricular white matter. She had an acquired immune deficiency syndrome (AIDS) encephalopathy of pure dominant pyramidal tract disorder without an intellectual deficit. Helper cell lymphocyte count (CD4) increased with the beginning of zidovudine (ZDV, also known as AZT) monotherapy but began to decrease after the 4th week to reach the baseline at 20th week. Zidovudine plus didanosine combination therapy was started at the 68th week, but because of intolerance, the combination was changed to ZDV plus lamivudine at the 98th week. By the 80th week, neither severe opportunistic infection nor deterioration of the neurological status was recognized, but chronic diarrhea appeared. The diarrhea advanced to the wasting syndrome at the age of 4 years and cytomegalovirus genome was confirmed in a biopsied specimen of the colon. Ganciclovir treatment was effective in stopping the diarrhea and increasing her bodyweight, but after the age of 5, resumption of diarrhea was followed by progressive emaciation and weakness. This work may provide some clues in treating children's AIDS.

Benzodiazepines, glia, and HIV-1 neuropathogenesis

Although the precise mechanisms whereby HIV-1 infection induces neurodegeneration have yet to be determined, a great deal of evidence has incriminated glial cells and the production of proinflammatory mediators in this pathologic process. For this reason, ideal therapeutic agents for the treatment of AIDS dementia would attenuate HIV-1 neuropathogenesis through both direct inhibition of viral expression and suppression of brain cell-produced immune mediators. Benzodiazepines (BDZs), such as Valium, are extensively prescribed drugs for anxiety disorders, which readily cross the blood-brain barrier and have demonstrated immunomodulatory properties. BDZs bind to primary human microglial cells, the principal site of HIV-1 replication in the brain, and inhibit lipopolysaccharide (LPS) induced tumour necrosis factor (TNF-alpha) production by these cells in a concentration-dependent manner. Treatment of HIV-1-infected primary human microglial, as well as mixed glial/neuronal, cell cultures with BDZs inhibits the expression of HIV-1 p24 antigen. BDZ-induced inhibition of HIV-1 expression in chronically infected promonocytic (U1) cells has been found to be associated with decreased activation of the nuclear transcription factor kappa B (NF-kappa B). Because HIV-1 expression is critically dependent on the cellular transcription machinery, inhibition of the activation of transcription factors, which participate in both HIV-1 expression and the production of neurotoxic immune mediators, by BDZ analogs may provide new therapeutic options for AIDS dementia.

The effects of human immunodeficiency virus in the central nervous system

More than a decade after the first description of HIV DNA in the nervous system the pathophysiology of HIVD remains largely enigmatic, with data supporting a number of potential mechanisms for the development of neuronal dysfunction. Nevertheless, a few key findings have considerable support in the literature devoted to this subject: 1. HIV dementia is caused by HIV itself; no other pathogen has been consistently found in the brains of patients with HIVD. 2. In comparison with other viral encephalopathies, there appears to be a significant discordance between the amount of virus being produced in the brains of patients with HIVD and the degree of neurological deterioration. 3. The key cell types responsible for viral production within the CNS are the resident macrophages or microglial cells. 4. Other elements within the CNS, particularly astrocytes, are probably infected with HIV as well, but all of these infections are highly restricted in terms of production of virus or viral structural proteins. 5. At least one component of the pathogenesis of HIVD may be the generation of neurotoxins by infected microglia, although the type of neurotoxin, and the specific compound most likely to be involved, are quite controversial. Advances with combination antiviral therapy have successfully reduced plasma viral load in a high proportion of individuals, leading to the speculation (previously almost heretical) that it may be possible to eradicate HIV completely from the systemic immune system. If that were the case, potential "sanctuary" sites such as the immunologically protected CNS might remain as important reservoirs for reseeding of lymphoid tissues. Microglia may be particularly suited for this purpose because they are long lived, can produce HIV for several weeks (at least in culture), and they are apparently relatively immune to virus-induced cytopathology such as syncytium formation. One can speculate about several scenarios resulting from the continued presence of replication-competent HIV within brain. In the worst case, a smoldering infection of the nervous system could lead to neurological deterioration without reinfection of systemic immune cells. The epidemiological data indicating that HIVD is a disease primarily associated with immunodeficiency suggest that the systemic immune system plays a role in maintaining virus residing within the CNS under control. Thus it is quite possible that this scenario would not occur for many years after the systemic infection is controlled. Alternatively, virus could be transported from the CNS by circulating lymphocytes and monocytes and reinfect systemic organs. This would necessitate restarting therapy for those individuals who were previously thought to be cured, but presumably virus within the CNS would not have developed resistance to antivirals. In either case, the techniques currently available do not permit an accurate assessment of CNS HIV load in living people, and this question will remain unanswered until antivirals are discontinued in a few individuals with persistently negative tests for systemic virus. In addition to this most critical question, the relationship between viral levels and HIVD is largely unexplored, as is the possibility that some strains are particularly virulent or neuroinvasive. Furthermore, the potential contribution of host genotype in the development of dementia is unknown. In view of the strong influence of major chemokine receptor (CCR5) truncations on HIV replication, it is entirely possible that more discrete genetic polymorphisms have a subtle effect on either brain invasion or virulence.

Axonal sprouting in hippocampus of cats infected with feline immunodeficiency virus (FIV)

Neurologic dysfunction and neuropathology are common findings in patients infected with HIV and in cats infected with feline immunodeficiency virus (FIV). The pathogenesis of lentivirus-associated alterations in the central nervous system (CNS) is multifactorial. Because seizures, alterations in memory, and behavioral changes are clinical manifestations in adults and children infected with HIV, we explored the possibility that changes in neuronal structure may occur in the hippocampus. To do this, we examined the dentate gyrus of FIV-infected cats, an animal model of HIV infection. Neuropathologic findings included gliosis within the hilus of the dentate gyrus and granule cell axonal sprouting. Using the Timm's method, which labels axons of dentate gyrus granule cells, abnormally high amounts of staining were observed in the inner one third of the molecular layer in 45% of FIV-infected cats (n = 11) and in none of the controls (n = 19). Prominent axonal sprouting was seen in three FIV-infected cats that were infected as kittens, suggesting that younger cats may be more susceptible. Axon reorganization of the dentate granule cells has been hypothesized to underlie complex partial seizure activity in human temporal lobe epilepsy. These results suggest that FIV infection causes granule cell axon reorganization in the hippocampus of cats. A similar neuropathogenetic mechanism may contribute to neurologic dysfunction in HIV-infected patients.

Unique HIV type 1 V3 region sequences derived from six different regions of brain: region-specific evolution within host-determined quasispecies

HIV type 1 viral quasispecies were amplified by polymerase chain reaction (PCR) in the hypervariable V3 region of gp120 from six different regions of the brain (right and left frontal; right and left parietal; and right and left occipital) and from the peripheral blood mononuclear cells (PBMCs) of a patient who died of AIDS dementia complex (ADC). Cloning and sequencing of the entire V3 region suggested the presence of genetically unique sequences in different regions of the brain. In contrast, the blood-derived viral quasispecies carried homogeneous sequences that were characterized by a single octapeptide crest motif (HLGPGSAF), a motif important in viral fusion. The brain-derived viral strains showed extensive sequence heterogeneity and the presence of seven different octapeptide and four different tetrapeptide crest motifs (HIGPGRAF, RIGPGRAF, HIGPGSAI, HLGPGSAF, HIGPESAI, HLGPESAI, and YLRPGSAF). In addition, the brain-derived strains were also characterized by variable net V3 loop charge and hydrophilicity, along with distinct amino acid changes specific to different brain regions. Together, the sequence and phylogenetic analyses are unique in identifying the complexity of a viral quasispecies and its independent regional evolution within the brain compartment. Uniquely divergent viral strains were identified in the frontal regions and their presence was further supported by the presence of multinucleated giant cells (characteristic of HIV encephalopathy) predominantly in the left and right frontal regions. In summary, these analyses suggest that genetically different populations of HIV-1 may be present in different brain compartments and confirm that specific neurotropic variants may exist.