AIDS dementia complex and HIV-1 brain infection: clinical-virological correlations

Changes in cerebrospinal fluid proteins across the spectrum of untreated and treated chronic HIV-1 infection

Using the Olink Explore 1536 platform, we measured 1,463 unique proteins in 303 cerebrospinal fluid (CSF) specimens from four clinical centers contributed by uninfected controls and 12 groups of people living with HIV-1 infection representing the spectrum of progressive untreated and treated chronic infection. We present three initial analyses of these measurements: an overview of the CSF protein features of the sample; correlations of the CSF proteins with CSF HIV-1 RNA and neurofilament light chain protein (NfL) concentrations; and comparison of CSF proteins in HIV-associated dementia (HAD) and neurosymptomatic CSF escape (NSE). These reveal a complex but coherent picture of CSF protein changes with highest concentrations of many proteins during CNS injury in the HAD and NSE groups and variable protein changes across the course of systemic HIV-1 progression that included two common patterns, designated as lymphoid and myeloid patterns, related to principal involvement of their underlying inflammatory cell lineages. Antiretroviral therapy reduced CSF protein perturbations, though not always to control levels. The dataset of these CSF protein measurements, along with background clinical information, is posted online. Extended studies of this unique dataset will supplement this report to provide more detailed characterization of the dynamic impact of HIV-1 infection on the CSF proteome across the spectrum of HIV-1 infection, advancing the mechanistic understanding of HIV-1-related CNS pathobiology.

Changes in Cerebrospinal Fluid Proteins across the Spectrum of Untreated and Treated Chronic HIV-1 Infection

Using the Olink Explore 1536 platform, we measured 1,463 unique proteins in 303 cerebrospinal fluid (CSF) specimens from four clinical centers that included uninfected controls and 12 groups of people living with HIV-1 infection representing the spectrum of progressive untreated and treated chronic infection. We present three initial analyses of these measurements: an overview of the CSF protein features of the sample; correlations of the CSF proteins with CSF HIV-1 RNA and neurofilament light chain protein (NfL) concentrations; and comparison of the CSF proteins in HIV-associated dementia ( HAD ) and neurosymptomatic CSF escape ( NSE ). These reveal a complex but coherent picture of CSF protein changes that includes highest concentrations of many proteins during CNS injury in the HAD and NSE groups and variable protein changes across the course of neuroasymptomatic systemic HIV-1 progression, including two common patterns, designated as lymphoid and myeloid patterns, related to the principal involvement of their underlying inflammatory cell lineages. Antiretroviral therapy reduced CSF protein perturbations, though not always to control levels. The dataset of these CSF protein measurements, along with background clinical information, is posted online. Extended studies of this unique dataset will provide more detailed characterization of the dynamic impact of HIV-1 infection on the CSF proteome across the spectrum of HIV-1 infection, and further the mechanistic understanding of HIV-1-related CNS pathobiology.

Modulation of OPRM1 Alternative Splicing by Morphine and HIV-1 Nef

Clinically used opioids, such as morphine, activate the mu opioid receptor (MOR) encoded by Opioid Receptor Mu 1 (OPRM1) gene. Examination of the opioid receptor genes showed that the human OPRM1 pre-mRNA undergoes extensive alternative splicing events and capable of expressing 21 isoforms. However, characterization of OPRM1 signaling is generalized, and only one isoform (MOR-1) has been extensively studied. Compounding this issue is the increasing significance of intravenous drug abuse in HIV neuropathogenesis. Here, we investigated the molecular impact of morphine and HIV-1 on regulation of OPRM1 pre-mRNA splicing in in vitro and in vivo models. Our results suggested that morphine treatment specifically induces the alternative splicing of MOR-1X isoform among the other isoforms analyzed in neuronal cells. Interestingly, alternative splicing and expression of MOR-1X isoform was also induced in postmortem brain tissues obtained from people with HIV (PWH). Additionally, treatment of control rats with morphine induced alternative splicing of MOR-1X in the brain regions involved in the reward pathways. More interestingly, HIV-1 transgenic (HIV-1Tg) rats, showed an additive induction of MOR-1X isoform with the exposure to morphine. To further assess the possible role of HIV secretory proteins in alternative splicing of OPRM1 gene, we analyzed the impact of HIV-1 Tat, gp120 and Nef proteins on alternative splicing of MOR-1X isoform. While the Tat and gp120 had no visible effects, treatment of neurons with Nef induced MOR-1X alternative splicing that was comparable to treatment with morphine. Altogether, our results suggest that HIV-1 may alter MOR isoform expression with Nef protein by amplifying the rate of MOR-1X alternative splicing induced by morphine.

HIV Dementia: A Bibliometric Analysis and Brief Review of the Top 100 Cited Articles

Dementia is a syndrome of cognitive impairment that affects an individual’s ability to live independently. The number of people living with dementia worldwide in 2015 was estimated at 47.47 million. The American Academy of Neurology (AAN) criteria for human immunodeficiency virus (HIV)-associated dementia (HAD) require an acquired abnormality in at least two cognitive (non-motor) domains and either an abnormality in motor function or specified neuropsychiatric/psychosocial domains. HIV is the most common cause of dementia below 60 years of age.

Citation frequencies are commonly used to assess the scholarly impact of any scientific publication in bibliometric analyses. It helps depict areas of higher interest in terms of research frequency and trends of citations in the published literature and identify under-explored domains of any field, providing useful insight and guidance for future research avenues. We used the database “Web of Science” (WOS) to search for the top 100 cited articles on HIV-associated dementia. The keywords “HIV dementia” and “HIV-associated neurocognitive disorders” (HAND) were used. The list was generated by two authors after excluding articles not pertaining to HIV dementia. The articles were then assigned to authors to extract data to make tables and graphical representations. Finally, the manuscript was organized and written describing the findings of the bibliometric study.

These 100 most cited articles on HIV dementia were published between years 1986 and 2016. The highest number of the articles was from 1999 (n=9). The year 1993-2007 contributed consistently two publications to the list. The articles are from 42 journals, and among them, the Annals of Neurology (n=16) and the Journal of Neurology (n=15) published most of the articles. Justin C. McArthur with 25 publications contributed the highest number of papers to the list by any author. The USA collaborated in the highest number of publications (n=87). American institutes were leading the list with the most publications. The Johns Hopkins University collaborated on 37 papers. The most widely studied aspect of HIV dementia was pathogenesis. Incidence and prevalence, clinical features, and pre- and post-highly active antiretroviral therapy (HAART) era were also discussed in the articles.

Beyond America, the research should be expanded to low-income countries and those affected more by HIV. Therefore, other countries and their institutes should participate more in HIV-associated dementia research. Anticipating the rising resistance to existing antiretrovirals, we should develop new therapeutic options. There is room for research in many aspects of HIV dementia care.

Brain aging and cardiovascular factors in HIV: a longitudinal volume and shape MRI study

OBJECTIVE

We aimed to examine the relative contributions of HIV infection, age, and cardiovascular risk factors to subcortical brain atrophy in people with HIV (PWH).

DESIGN

Longitudinal observational study.

METHODS

Virally suppressed PWH with low neuropsychological confounds (n  = 75) and demographically matched HIV-negative controls (n = 31) completed baseline and 18-month follow-up MRI scans, neuropsychological evaluation, cardiovascular assessments, and HIV laboratory tests. PWH were evaluated for HIV-associated neurocognitive disorder (HAND). Subcortical volumes were extracted with Freesurfer after removal of white matter hyperintensities. Volumetric and shape analyses were conducted using linear mixed-effect models incorporating interactions between age, time, and each of HIV status, HAND status, HIV disease factors, and cardiovascular markers.

RESULTS

Across baseline and follow-up PWH had smaller volumes of most subcortical structures compared with HIV-negative participants. In addition, over time older PWH had a more rapid decline in caudate volumes (P  = 0.041), predominantly in the more severe HAND subgroups (P = 0.042). Higher CD4+ cell counts had a protective effect over time on subcortical structures for older participants with HIV. Increased cardiovascular risk factors were associated with smaller volumes across baseline and follow-up for most structures, although a more rapid decline over time was observed for striatal volumes. There were no significant shape analyses findings.

CONCLUSION

The study demonstrates a three-hit model of general (as opposed to localized) subcortical injury in PWH: HIV infection associated with smaller volumes of most subcortical structures, HIV infection and aging synergy in the striatum, and cardiovascular-related injury linked to early and more rapid striatal atrophy.

The Role of Pathogens and Anti-Infective Agents in Parkinson's Disease, from Etiology to Therapeutic Implications

Parkinson's disease is a debilitating neurodegenerative disorder whose etiology is still unclear, hampering the development of effective treatments. There is an urgent need to identify the etiology and provide further effective treatments. Recently, accumulating evidence has indicated that infection may play a role in the etiology of Parkinson's disease. The infective pathogens may act as a trigger for Parkinson's disease, the most common of which are hepatitis C virus, influenza virus, and Helicobacter pylori. In addition, gut microbiota is increasingly recognized to influence brain function through the gut-brain axis, showing an important role in the pathogenesis of Parkinson's disease. Furthermore, a series of anti-infective agents exhibit surprising neuroprotective effects via various mechanisms, such as interfering with α-synuclein aggregation, inhibiting neuroinflammation, attenuating oxidative stress, and preventing from cell death, independent of their antimicrobial effects. The pleiotropic agents affect important events in the pathogenesis of Parkinson's disease. Moreover, most of them are less toxic, clinically safe and have good blood-brain penetrability, making them hopeful candidates for the treatment of Parkinson's disease. However, the use of antibiotics and subsequent gut dysbiosis may also play a role in Parkinson's disease, making the long-term effects of anti-infective drugs worthy of further consideration and exploration. This review summarizes the current evidence for the association between infective pathogens and Parkinson's disease and subsequently explores the application prospects of anti-infective drugs in Parkinson's disease treatment, providing novel insights into the pathogenesis and treatment of Parkinson's disease.

Redistribution of brain glucose metabolism in people with HIV after antiretroviral therapy initiation

OBJECTIVE

We evaluated brain glucose metabolism in people living with HIV (PWH) with [18F]-Fluoro-Deoxyglucose (FDG) PET/computed tomography (CT) before and after antiretroviral therapy (ART) initiation.

DESIGN

We conducted a longitudinal study wherein ART-naive late-presenting untreated PWH with CD4+ cell counts less than 100 cells/μl were prospectively assessed for FDG uptake at baseline and at 4-8 weeks (n = 22) and 19-26 months (n = 11) following ART initiation.

METHODS

Relative uptake in the subcortical regions (caudate, putamen and thalamus) and cortical regions (frontal, parietal, temporal and occipital cortices) were compared across time and correlated with biomarkers of disease activity and inflammation, in addition to being compared with a group of uninfected individuals (n = 10).

RESULTS

Before treatment initiation, putaminal and caudate relative FDG uptake values in PWH were significantly higher than in uninfected controls. Relative putaminal and thalamic uptake significantly decreased shortly following ART initiation, while frontal cortex values significantly increased. FDG uptake changes correlated with changes in CD4+ cell counts and viral load, and, in the thalamus, with IL-6R and sCD14. Approximately 2 years following ART initiation, there was further decrease in subcortical relative uptake values, reaching levels below those of uninfected controls.

CONCLUSION

Our findings support pretreatment basal ganglia and thalamic neuroinflammatory changes in PWH, which decrease after treatment with eventual unmasking of long-term irreversible neuronal damage. Meanwhile, increased frontal cortex metabolism following ART initiation suggests reversible cortical dysfunction which improves with virologic control and increased CD4+ cell counts. Early initiation of treatment after HIV diagnosis and secondary control of inflammation are thus necessary to halt neurological damage in PWH.

Compartmentalization of cerebrospinal fluid inflammation across the spectrum of untreated HIV-1 infection, central nervous system injury and viral suppression

OBJECTIVE

To characterize the evolution of central nervous system (CNS) inflammation in HIV-1 infection applying a panel of cerebrospinal fluid (CSF) inflammatory biomarkers to grouped subjects representing a broad spectrum of systemic HIV-1 immune suppression, CNS injury and viral control.

METHODS

This is a cross-sectional analysis of archived CSF and blood samples, assessing concentrations of 10 functionally diverse soluble inflammatory biomarkers by immunoassays in 143 HIV-1-infected subjects divided into 8 groups: untreated primary HIV-1 infection (PHI); four untreated groups defined by their blood CD4+ T lymphocyte counts; untreated patients presenting with subacute HIV-associated dementia (HAD); antiretroviral-treated subjects with ≥1 years of plasma viral suppression; and untreated elite controllers. Twenty HIV-1-uninfected controls were included for comparison. Background biomarkers included blood CD4+ and CD8+ T lymphocytes, CSF and blood HIV-1 RNA, CSF white blood cell (WBC) count, CSF/blood albumin ratio, CSF neurofilament light chain (NfL), and CSF t-tau.

FINDINGS

HIV-1 infection was associated with a broad compartmentalized CSF inflammatory response that developed early in its course and changed with systemic disease progression, development of neurological injury, and viral suppression. CSF inflammation in untreated individuals without overt HAD exhibited at least two overall patterns of inflammation as blood CD4+ T lymphocytes decreased: one that peaked at 200-350 blood CD4+ T cells/μL and associated with lymphocytic CSF inflammation and HIV-1 RNA concentrations; and a second that steadily increased through the full range of CD4+ T cell decline and associated with macrophage responses and increasing CNS injury. Subacute HAD was distinguished by a third inflammatory profile with increased blood-brain barrier permeability and robust combined lymphocytic and macrophage CSF inflammation. Suppression of CSF and blood HIV-1 infections by antiretroviral treatment and elite viral control were associated with reduced CSF inflammation, though not fully to levels found in HIV-1 seronegative controls.

Association of Immunosuppression and Viral Load With Subcortical Brain Volume in an International Sample of People Living With HIV

Importance

Despite more widely accessible combination antiretroviral therapy (cART), HIV-1 infection remains a global public health challenge. Even in treated patients with chronic HIV infection, neurocognitive impairment often persists, affecting quality of life. Identifying the neuroanatomical pathways associated with infection in vivo may delineate the neuropathologic processes underlying these deficits. However, published neuroimaging findings from relatively small, heterogeneous cohorts are inconsistent, limiting the generalizability of the conclusions drawn to date.

Objective

To examine structural brain associations with the most commonly collected clinical assessments of HIV burden (CD4+ T-cell count and viral load), which are generalizable across demographically and clinically diverse HIV-infected individuals worldwide.

Design, Setting, and Participants

This cross-sectional study established the HIV Working Group within the Enhancing Neuro Imaging Genetics Through Meta Analysis (ENIGMA) consortium to pool and harmonize data from existing HIV neuroimaging studies. In total, data from 1295 HIV-positive adults were contributed from 13 studies across Africa, Asia, Australia, Europe, and North America. Regional and whole brain segmentations were extracted from data sets as contributing studies joined the consortium on a rolling basis from November 1, 2014, to December 31, 2019.

Main Outcomes and Measures

Volume estimates for 8 subcortical brain regions were extracted from T1-weighted magnetic resonance images to identify associations with blood plasma markers of current immunosuppression (CD4+ T-cell counts) or detectable plasma viral load (dVL) in HIV-positive participants. Post hoc sensitivity analyses stratified data by cART status.

Results

After quality assurance, data from 1203 HIV-positive individuals (mean [SD] age, 45.7 [11.5] years; 880 [73.2%] male; 897 [74.6%] taking cART) remained. Lower current CD4+ cell counts were associated with smaller hippocampal (mean [SE] β = 16.66 [4.72] mm3 per 100 cells/mm3; P < .001) and thalamic (mean [SE] β = 32.24 [8.96] mm3 per 100 cells/mm3; P < .001) volumes and larger ventricles (mean [SE] β = -391.50 [122.58] mm3 per 100 cells/mm3; P = .001); in participants not taking cART, however, lower current CD4+ cell counts were associated with smaller putamen volumes (mean [SE] β = 57.34 [18.78] mm3 per 100 cells/mm3; P = .003). A dVL was associated with smaller hippocampal volumes (d = -0.17; P = .005); in participants taking cART, dVL was also associated with smaller amygdala volumes (d = -0.23; P = .004).

Conclusions and Relevance

In a large-scale international population of HIV-positive individuals, volumes of structures in the limbic system were consistently associated with current plasma markers. Our findings extend beyond the classically implicated regions of the basal ganglia and may represent a generalizable brain signature of HIV infection in the cART era.

Neuroimaging Advances in Diagnosis and Differentiation of HIV, Comorbidities, and Aging in the cART Era

In the "cART era" of more widely available and accessible treatment, aging and HIV-related comorbidities, including symptoms of brain dysfunction, remain common among HIV-infected individuals on suppressive treatment. A better understanding of the neurobiological consequences of HIV infection is essential for developing thorough treatment guidelines and for optimizing long-term neuropsychological outcomes and overall brain health. In this chapter, we first summarize magnetic resonance imaging (MRI) methods used in over two decades of neuroHIV research. These methods evaluate brain volumetric differences and circuitry disruptions in adults living with HIV, and help map clinical correlations with brain function and tissue microstructure. We then introduce and discuss aging and associated neurological complications in people living with HIV, and processes by which infection may contribute to the risk for late-onset dementias. We describe how new technologies and large-scale international collaborations are helping to disentangle the effect of genetic and environmental risk factors on brain aging and neurodegenerative diseases. We provide insights into how these advances, which are now at the forefront of Alzheimer's disease research, may advance the field of neuroHIV. We conclude with a summary of how we see the field of neuroHIV research advancing in the decades to come and highlight potential clinical implications.

State of the Mind: Growing up with HIV

Human immunodeficiency virus (HIV) is a neurotropic virus that has a detrimental impact on the developing central nervous system (CNS) of children growing up with perinatal HIV (PHIV) due to a combination of pathophysiological processes related to direct viral cytopathic effects and immune activation. This leads to a spectrum of neurocognitive impairment ranging from severe encephalopathy to subtle domain-specific cognitive impairments, as well as psychological disorders that are compounded by HIV-related stigma and sociodemographic factors that disproportionately affect PHIV children. Early commencement and consistent use of combination antiretroviral therapy (cART) has resulted in a dramatic improvement in neuropsychological outcomes for PHIV children; however, they remain vulnerable to cognitive impairment and psychological disorders, as evidenced by imaging findings, randomised clinical trials and observational studies. An optimal neuroprotective cART regimen remains elusive in children, but systemic viral suppression, regular neurocognitive and psychological screening and ready access to neuropsychological management strategies are key components for optimising neuropsychological outcomes. However, a lack of standardised and validated screening tools, particularly in resource-limited settings, hinders a precise understanding of the nature, prevalence and associations between neuropsychological symptomatology and HIV health. This article reviews the natural history, cellular pathophysiology and structural and functional imaging findings for children growing up with HIV, as well as summarising management strategies related to antiretroviral therapy, screening tools and specific interventions for neurocognitive impairments and psychological disorders.

Neuroinflammation associates with antioxidant heme oxygenase-1 response throughout the brain in persons living with HIV

Previous studies showed that persons living with HIV (PLWH) demonstrate higher brain prefrontal cortex neuroinflammation and immunoproteasome expression compared to HIV-negative individuals; these associate positively with HIV levels. Lower expression of the antioxidant enzyme heme oxygenase 1 (HO-1) was observed in PLWH with HIV-associated neurocognitive impairment (HIV-NCI) compared to neurocognitively normal PLWH. We hypothesized that similar expression patterns occur throughout cortical, subcortical, and brainstem regions in PLWH, and that neuroinflammation and immunoproteasome expression associate with lower expression of neuronal markers. We analyzed autopsied brains (15 regions) from 9 PLWH without HIV-NCI and 7 matched HIV-negative individuals. Using Western blot and RT-qPCR, we quantified synaptic, inflammatory, immunoproteasome, endothelial, and antioxidant biomarkers, including HO-1 and its isoform heme oxygenase 2 (HO-2). In these PLWH without HIV-NCI, we observed higher expression of neuroinflammatory, endothelial, and immunoproteasome markers in multiple cortical and subcortical regions compared to HIV-negative individuals, suggesting a global brain inflammatory response to HIV. Several regions, including posterior cingulate cortex, globus pallidus, and cerebellum, showed a distinct pattern of higher type I interferon (IFN)-stimulated gene and immunoproteasome expression. PLWH without HIV-NCI also had (i) stable or higher HO-1 expression and positive associations between (ii) HO-1 and HIV levels (CSF, plasma) and (iii) HO-1 expression and neuroinflammation, in multiple cortical, subcortical, and brainstem regions. We observed no differences in synaptic marker expression, suggesting little, if any, associated neuronal injury. We speculate that this may reflect a neuroprotective effect of a concurrent HO-1 antioxidant response despite global neuroinflammation, which will require further investigation.

New Potential Axes of HIV Neuropathogenesis with Relevance to Biomarkers and Treatment

Human immunodeficiency virus (HIV)-associated neurocognitive disorders (HAND) affect approximately half of people living with HIV despite viral suppression with antiretroviral therapies and represent a major cause of morbidity. HAND affects activities of daily living including driving, using the Internet and, importantly, maintaining drug adherence. Whilst viral suppression with antiretroviral therapies (ART) has reduced the incidence of severe dementia, mild neurocognitive impairments continue to remain prevalent. The neuropathogenesis of HAND in the context of viral suppression remains ill-defined, but underlying neuroinflammation is likely central and driven by a combination of chronic intermittent low-level replication of whole virus or viral components, latent HIV infection, peripheral inflammation possibly from a disturbed gut microbiome or chronic cellular dysfunction in the central nervous system. HAND is optimally diagnosed by clinical assessment with imaging and neuropsychological testing, which can be difficult to perform in resource-limited settings. Thus, the identification of biomarkers of disease is a key focus of the field. In this chapter, recent advances in the pathogenesis of HAND and biomarkers that may aid its diagnosis and treatment will be discussed.

The impact of HIV central nervous system persistence on pathogenesis

: The persistence of HIV in the central nervous system is somewhat controversial particularly in the context of HIV viral suppression from combined antiretroviral therapy. Further, its significance in relation to HIV pathogenesis in the context of HIV-associated neurocognitive disorders, systemic HIV pathogenesis, and eradication in general, but especially from the brain, are even more contentious. This review will discuss each of these aspects in detail, highlighting new data, particularly from recent conference presentations.

Neurological manifestations, laboratory and neuroimaging features in HIV-infected patients

Objectives:

To present detailed information regarding these aspects in Human Immunodeficiency Virus (HIV)-infected patients making an effort to improve the recognition of neurological complications of HIV infection.

Methods:

This retrospective study analyzed the clinical manifestations, laboratory and neuroimaging results of HIV-infected patients with neurological complications at Xuanwu hospital, Beijing, China from January 2011 to December 2014, one of top-rated hospitals in Beijing, China.

Results:

A diverse range of clinical diagnoses was identified, including encephalopathy, meningoencephalitis, peripheral neuropathy, multiple sclerosis, cerebral infarction and lymphoma associated with HIV infection. The mostly observed neurological disorders were motor/sensory deficits in the limbs (75%), cognitive impairments (42%) and fever (33%). Non-specific results of laboratory tests, including elevated erythrocyte sedimentation rate (ESR), cerebrospinal fluid (CSF) protein concentration and IgG, were found. Brain Magnetic Resonance Imaging (MRI) abnormalities displayed a variety of patterns and distributions due to diverse clinical profiles.

Conclusion:

The clinical scenarios of HIV-infected patients are remarkably diverse and complex. Etiological tests would be cardinal to make more definitive diagnosis for HIV-infected patients. Prospective studies with follow-up were needed to bring more accurate information.

Progressive brain atrophy in chronically infected and treated HIV+ individuals

Growing evidence points to persistent neurological injury in chronic HIV infection. It remains unclear whether chronically HIV-infected individuals on combined antiretroviral therapy (cART) develop progressive brain injury and impaired neurocognitive function despite successful viral suppression and immunological restoration. In a longitudinal neuroimaging study for the HIV Neuroimaging Consortium (HIVNC), we used tensor-based morphometry to map the annual rate of change of regional brain volumes (mean time interval 1.0 ± 0.5 yrs), in 155 chronically infected and treated HIV+ participants (mean age 48.0 ± 8.9 years; 83.9% male) . We tested for associations between rates of brain tissue loss and clinical measures of infection severity (nadir or baseline CD4+ cell count and baseline HIV plasma RNA concentration), HIV duration, cART CNS penetration-effectiveness scores, age, as well as change in AIDS Dementia Complex stage. We found significant brain tissue loss across HIV+ participants, including those neuro-asymptomatic with undetectable viral loads, largely localized to subcortical regions. Measures of disease severity, age, and neurocognitive decline were associated with greater atrophy. Chronically HIV-infected and treated individuals may undergo progressive brain tissue loss despite stable and effective cART, which may contribute to neurocognitive decline. Understanding neurological complications of chronic infection and identifying factors associated with atrophy may help inform strategies to maintain brain health in people living with HIV.

Nicotinic Acetylcholine Receptors in HIV: Possible Roles During HAND and Inflammation

Infection with the human immunodeficiency virus (HIV) remains a threat to global health. Since its discovery, many efforts have been directed at understanding the mechanisms and consequences of infection. Although there have been substantial advances since the advent of antiretroviral therapy, there are still complications that significantly compromise the health of infected patients, particularly, chronic inflammation and HIV-associated neurocognitive disorders (HAND). In this review, a new perspective is addressed in the field of HIV, where the alpha7 nicotinic acetylcholine receptor (α7-nAChR) is the protagonist. We comprehensively discuss the available evidence implicating α7-nAChRs in the context of HIV and provide possible explanations about its role in HAND and inflammation in both the central nervous system and the periphery.

Individuals with HIV-1 Subtype C Infection and Cryptococcal Meningitis Exhibit Viral Genetic Intermixing of HIV-1 Between Plasma and Cerebrospinal Fluid and a High Prevalence of CXCR4-Using Variants

The genotypic properties of human immunodeficiency virus type 1 (HIV-1) subtype C in individuals presenting with cryptococcal meningitis (CM) are not well established. Employing single-genome amplification as well as bulk PCR, cloning and sequencing strategies, we evaluated the genetic properties of HIV-1 subtype C env in 16 antiretroviral therapy-naive study participants with CM. Eleven of the 16 participants had matched blood plasma and cerebrospinal fluid (CSF) evaluated, with the rest having either a plasma or CSF sample evaluated. Before antiretroviral therapy initiation, matched plasma and CSF-derived env sequences of all 11 participants displayed genetic intermixing between the two compartments. Overall, 7 of the 16 (∼43.8%) participants harbored CXCR4-using variants in plasma and/or CSF, according to coreceptor usage prediction algorithms. This study suggests that HIV-1 subtype C genetic intermixing between peripheral blood and the central nervous system is common in individuals presenting with CM, and that CXCR4 usage is present in one or both compartments in approximately 44% of individuals.

HIV-associated neurocognitive disorder

Human immunodeficiency virus (HIV)-associated neurocognitive disorder (HAND) affects roughly half the HIV-positive population. The symptoms of cognitive slowing, poor concentration, and memory problems can impact on everyday life. Its diagnosis is validated where possible by identifying deficits in two cognitive domains on neuropsychologic testing in patients either with or without symptoms. Corroborating evidence may be found on imaging, blood tests, and cerebrospinal fluid analysis, though sensitive and specific biomarkers are currently lacking. The introduction of combined antiretroviral therapy in the 1990s has generated a therapeutic paradox whereby the number of severe cases of HAND has fallen, yet milder forms continue to rise in prevalence. New emphasis has been placed on identifying the cause of apparent ongoing HIV infection and inflammation of the central nervous system (CNS) in the face of durable systemic viral suppression, and how this equates to the neuronal dysfunction underlying HAND. The interaction with aging and comorbidities is becoming increasingly common as the HIV-positive population enters older adulthood, with neurodegenerative, metabolic, and vascular causes of cognitive impairment combining and probably accelerating in the context of chronic HIV infection. Therapies targeted to the CNS, but without neurotoxic side-effects, are being investigated to attempt to reduce the likelihood of developing, and improving, HAND.

HIV neuropathology

Primary human immunodeficiency virus (HIV) neuropathologies can affect all levels of the neuraxis and occur in all stages of natural history disease. Some, like HIV encephalitis, HIV myelitis, and diffuse infiltrative lymphocytosis of peripheral nerve, reflect productive infection of the nervous system; others, like vacuolar myelopathy, distal symmetric polyneuropathy, and central and peripheral nervous system demyelination, are not clearly related to regional viral replication, and reflect more complex cascades of dysregulated host immunity and metabolic dysfunction. In pediatric patients, the spectrum of neuropathology is altered by the impacts of HIV on a developing nervous system, with microcephaly, abundant brain mineralization, and corticospinal tract degeneration as examples of this unique interaction. With efficacious therapies, CD8 T-cell encephalitis is emerging as a significant entity; often this is clinically recognized as immune reconstitution inflammatory syndrome, but has also been described in the context of viral escape and treatment interruption. The relationship of HIV neuropathology to clinical symptoms is sometimes straightforward, and sometimes mysterious, as individuals can manifest significant deficits in the absence of discrete lesions. However, at all stages of the natural history disease, neuroinflammation is abundant, and critical to the generation of clinical abnormality. Neuropathologic and neurobiologic investigations will be central to understanding HIV nervous system disorders in the era of efficacious therapies.

HIV, Tat and dopamine transmission

Human Immunodeficiency Virus (HIV) is a progressive infection that targets the immune system, affecting more than 37 million people around the world. While combinatorial antiretroviral therapy (cART) has lowered mortality rates and improved quality of life in infected individuals, the prevalence of HIV associated neurocognitive disorders is increasing and HIV associated cognitive decline remains prevalent. Recent research has suggested that HIV accessory proteins may be involved in this decline, and several studies have indicated that the HIV protein transactivator of transcription (Tat) can disrupt normal neuronal and glial function. Specifically, data indicate that Tat may directly impact dopaminergic neurotransmission, by modulating the function of the dopamine transporter and specifically damaging dopamine-rich regions of the CNS. HIV infection of the CNS has long been associated with dopaminergic dysfunction, but the mechanisms remain undefined. The specific effect(s) of Tat on dopaminergic neurotransmission may be, at least partially, a mechanism by which HIV infection directly or indirectly induces dopaminergic dysfunction. Therefore, precisely defining the specific effects of Tat on the dopaminergic system will help to elucidate the mechanisms by which HIV infection of the CNS induces neuropsychiatric, neurocognitive and neurological disorders that involve dopaminergic neurotransmission. Further, this will provide a discussion of the experiments needed to further these investigations, and may help to identify or develop new therapeutic approaches for the prevention or treatment of these disorders in HIV-infected individuals.

HIV-associated synaptic degeneration

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

Expression of CHRFAM7A and CHRNA7 in neuronal cells and postmortem brain of HIV-infected patients: considerations for HIV-associated neurocognitive disorder

Despite the recent advances in antiretroviral therapy, human immunodeficiency virus type 1 (HIV-1) remains a global health threat. HIV-1 affects the central nervous system by releasing viral proteins that trigger neuronal death and neuroinflammation, and promotes alterations known as HIV-associated neurocognitive disorders (HAND). This disorder is not fully understood, and no specific treatments are available. Recently, we demonstrated that the HIV-1 envelope protein gp120IIIB induces a functional upregulation of the α7-nicotinic acetylcholine receptor (α7) in neuronal cells. Furthermore, this upregulation promotes cell death that can be abrogated with receptor antagonists, suggesting that α7 may play an important role in the development of HAND. The partial duplication of the gene coding for the α7, known as CHRFAM7A, negatively regulates α7 expression but its role in HIV infection has not been studied. Hence, we studied both CHRNA7 and CHRFAM7A regulation patterns in various gp120IIIB in vitro conditions. In addition, we measured CHRNA7 and CHRFAM7A expression levels in postmortem brain samples from patients suffering from different stages of HAND. Our results demonstrate the induction of CHRNA7 expression accompanied by a significant downregulation of CHRFAM7A in neuronal cells when exposed to pathophysiological concentrations of gp120IIIB. Our results suggest a dysregulation of CHRFAM7A and CHRNA7 expressions in the basal ganglia from postmortem brain samples of HIV+ subjects and expand the current knowledge about the consequences of HIV infection in the brain.

[HIV 1-associated neurocognitive disorder: current epidemiology, pathogenesis, diagnosis and management]

By restoring the immunological function the modern antiretroviral treatment of human immunodeficiency virus (HIV-1) infection has considerably lowered the incidence of opportunistic infections. As opposed to the classical manifestations of HIV-induced immunosuppression the incidence and prevalence of HIV-associated neurocognitive disorders (HAND) has not noticeably decreased and HAND continues to be relevant in daily clinical practice. At present, HAND occurs in earlier stages of HIV infection, and the clinical course differs from that before the introduction of combination antiretroviral treatment (cART). The predominant clinical manifestation is a subcortical dementia with deficits in the domains attention, concentration and memory. Signs of central motor pathway lesions have become less frequent and less prominent. Prior to the advent of cART the cerebral dysfunction could at least partially be explained by the viral load and by virus-associated histopathological findings. In patients with at least partially successfully treated infections, this relationship no longer exists, but a plethora of poorly understood immunological and probably toxic phenomena are under discussion.This consensus paper summarizes the progress made in the last 12 years in the field of HAND and provides suggestions for the diagnostic and therapeutic management.

HIV effects on age-associated neurocognitive dysfunction: premature cognitive aging or neurodegenerative disease?

Marked improvements in survival and health outcome for people infected with HIV have occurred since the advent of combination antiretroviral therapy over a decade ago. Yet HIV-associated neurocognitive disorders continue to occur with an alarming prevalence. This may reflect the fact that infected people are now living longer with chronic infection. There is mounting evidence that HIV exacerbates age-associated cognitive decline. Many middle-aged HIV-infected people are experiencing cognitive decline similar that to that found among much older adults. An increased prevalence of vascular and metabolic comorbidities has also been observed and is greatest among older adults with HIV. Premature age-associated neurocognitive decline appears to be related to structural and functional brain changes on neuroimaging, and of particular concern is the fact that pathology indicative of neurodegenerative disease has been shown to occur in the brains of HIV-infected people. Yet notable differences also exist between the clinical presentation and brain disturbances occurring with HIV and those occurring in neurodegenerative conditions such as Alzheimer’s disease. HIV interacts with the aging brain to affect neurological structure and function. However, whether this interaction directly affects neurodegenerative processes, accelerates normal cognitive aging, or contributes to a worsening of other comorbidities that affect the brain in older adults remains an open question. Evidence for and against each of these possibilities is reviewed.

Genetic diversity and proviral DNA load in different neural compartments of HIV-1 subtype C infection

In India, the low prevalence of HIV-associated dementia (HAD) in the Human immunodeficiency virus type 1 (HIV-1) subtype C infection is quite paradoxical given the high-rate of macrophage infiltration into the brain. Whether the direct viral burden in individual brain compartments could be associated with the variability of the neurologic manifestations is controversial. To understand this paradox, we examined the proviral DNA load in nine different brain regions and three different peripheral tissues derived from ten human subjects at autopsy. Using a highly sensitive TaqMan probe-based real-time PCR, we determined the proviral load in multiple samples processed in parallel from each site. Unlike previously published reports, the present analysis identified uniform proviral distribution among the brain compartments examined without preferential accumulation of the DNA in any one of them. The overall viral DNA burden in the brain tissues was very low, approximately 1 viral integration per 1000 cells or less. In a subset of the tissue samples tested, the HIV DNA mostly existed in a free unintegrated form. The V3-V5 envelope sequences, demonstrated a brain-specific compartmentalization in four of the ten subjects and a phylogenetic overlap between the neural and non-neural compartments in three other subjects. The envelope sequences phylogenetically belonged to subtype C and the majority of them were R5 tropic. To the best of our knowledge, the present study represents the first analysis of the proviral burden in subtype C postmortem human brain tissues. Future studies should determine the presence of the viral antigens, the viral transcripts, and the proviral DNA, in parallel, in different brain compartments to shed more light on the significance of the viral burden on neurologic consequences of HIV infection.

CCR5 knockout prevents neuronal injury and behavioral impairment induced in a transgenic mouse model by a CXCR4-using HIV-1 glycoprotein 120

The innate immune system has been implicated in several neurodegenerative diseases, including HIV-1-associated dementia. In this study, we show that genetic ablation of CCR5 prevents microglial activation and neuronal damage in a transgenic model of HIV-associated brain injury induced by a CXCR4-using viral envelope gp120. The CCR5 knockout (KO) also rescues spatial learning and memory in gp120-transgenic mice. However, the CCR5KO does not abrogate astrocytosis, indicating it can occur independently from neuronal injury and behavioral impairment. To characterize further the neuroprotective effect of CCR5 deficiency we performed a genome-wide gene expression analysis of brains from HIVgp120tg mice expressing or lacking CCR5 and nontransgenic controls. A comparison with a human brain microarray study reveals that brains of HIVgp120tg mice and HIV patients with neurocognitive impairment share numerous differentially regulated genes. Furthermore, brains of CCR5 wild-type and CCR5KO gp120tg mice express markers of an innate immune response. One of the most significantly upregulated factors is the acute phase protein lipocalin-2 (LCN2). Using cerebrocortical cell cultures, we find that LCN2 is neurotoxic in a CCR5-dependent fashion, whereas inhibition of CCR5 alone is not sufficient to abrogate neurotoxicity of a CXCR4-using gp120. However, the combination of pharmacologic CCR5 blockade and LCN2 protects neurons from toxicity of a CXCR4-using gp120, thus recapitulating the finding in CCR5-deficient gp120tg mouse brain. Our study provides evidence for an indirect pathologic role of CCR5 and a novel protective effect of LCN2 in combination with inhibition of CCR5 in HIV-associated brain injury.

Predictors of CNS injury as measured by proton magnetic resonance spectroscopy in the setting of chronic HIV infection and CART

The reasons for persistent brain dysfunction in chronically HIV-infected persons on stable combined antiretroviral therapies (CART) remain unclear. Host and viral factors along with their interactions were examined in 260 HIV-infected subjects who underwent magnetic resonance spectroscopy (MRS). Metabolite concentrations (NAA/Cr, Cho/Cr, MI/Cr, and Glx/Cr) were measured in the basal ganglia, the frontal white matter, and gray matter, and the best predictive models were selected using a bootstrap-enhanced Akaike information criterion (AIC). Depending on the metabolite and brain region, age, race, HIV RNA concentration, ADC stage, duration of HIV infection, nadir CD4, and/or their interactions were predictive of metabolite concentrations, particularly the basal ganglia NAA/Cr and the mid-frontal NAA/Cr and Glx/Cr, whereas current CD4 and the CPE index rarely or did not predict these changes. These results show for the first time that host and viral factors related to both current and past HIV status contribute to persisting cerebral metabolite abnormalities and provide a framework for further understanding neurological injury in the setting of chronic and stable disease.

Disrupted cerebral metabolite levels and lower nadir CD4 + counts are linked to brain volume deficits in 210 HIV-infected patients on stable treatment

Cognitive impairment and brain injury are common in people with HIV/AIDS, even when viral replication is effectively suppressed with combined antiretroviral therapies (cART). Metabolic and structural abnormalities may promote cognitive decline, but we know little about how these measures relate in people on stable cART. Here we used tensor-based morphometry (TBM) to reveal the 3D profile of regional brain volume variations in 210 HIV + patients scanned with whole-brain MRI at 1.5 T (mean age: 48.6 ± 8.4 years; all receiving cART). We identified brain regions where the degree of atrophy was related to HIV clinical measures and cerebral metabolite levels assessed with magnetic resonance spectroscopy (MRS). Regional brain volume reduction was linked to lower nadir CD4 + count, with a 1–2% white matter volume reduction for each 25-point reduction in nadir CD4 +. Even so, brain volume measured by TBM showed no detectable association with current CD4 + count, AIDS Dementia Complex (ADC) stage, HIV RNA load in plasma or cerebrospinal fluid (CSF), duration of HIV infection, antiretroviral CNS penetration-effectiveness (CPE) scores, or years on cART, after controlling for demographic factors, and for multiple comparisons. Elevated glutamate and glutamine (Glx) and lower N-acetylaspartate (NAA) in the frontal white matter, basal ganglia, and mid frontal cortex — were associated with lower white matter, putamen and thalamus volumes, and ventricular and CSF space expansion. Reductions in brain volumes in the setting of chronic and stable disease are strongly linked to a history of immunosuppression, suggesting that delays in initiating cART may result in imminent and irreversible brain damage.

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We mapped the 3D pattern of brain abnormalities in 210 HIV patients on stable cART.

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Brain atrophy was linked to MRS metabolite disturbances reflecting neuronal injury.

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Lower nadir CD4 + count was associated with greater white matter atrophy.

Progressive cerebral injury in the setting of chronic HIV infection and antiretroviral therapy

Emerging evidence suggests that CNS injury and neurocognitive impairment persist in the setting of chronic HIV infection and combination antiretroviral therapy (CART). Yet, whether neurological injury can progress in this setting remains uncertain. Magnetic resonance spectroscopy and neurocognitive and clinical assessments were performed over 2 years in 226 HIV-infected individuals on stable CART, including 138 individuals who were neurocognitively asymptomatic (NA). Concentrations of N-acetylaspartate (NAA), creatine (Cr), choline (Cho), myoinositol, and glutamate/glutamine (Glx) were measured in the midfrontal cortex (MFC), frontal white matter (FWM), and basal ganglia (BG). Longitudinal changes in metabolite levels were determined using linear mixed effect models, as were metabolite changes in relation to global neurocognitive function. HIV-infected subjects showed significant annual decreases in brain metabolite levels in all regions examined, including NAA (2.95 %) and Cho (2.61 %) in the FWM; NAA (1.89 %), Cr (1.84 %), Cho (2.19 %), and Glx (6.05 %) in the MFC; and Glx (2.80 %) in the BG. Similar metabolite decreases were observed in the NA and subclinically impaired subgroups, including subjects with virologic suppression in plasma and CSF. Neurocognitive decline was associated with longitudinal decreases in Glx in the FWM and the BG, and in NAA in the BG. Widespread progressive changes in the brain, including neuronal injury, occur in chronically HIV-infected persons despite stable antiretroviral treatment and virologic suppression and can lead to neurocognitive declines. The basis for these findings is poorly understood and warrants further study.

A parallel genome-wide mRNA and microRNA profiling of the frontal cortex of HIV patients with and without HIV-associated dementia shows the role of axon guidance and downstream pathways in HIV-mediated neurodegeneration

BACKGROUND

HIV-associated dementia (HAD) is the most common dementia type in young adults less than 40 years of age. Although the neurotoxins, oxidative/metabolic stress and impaired activity of neurotrophic factors are believed to be underlying reasons for the development of HAD, the genomic basis, which ultimately defines the virus-host interaction and leads to neurologic manifestation of HIV disease is lacking. Therefore, identifying HIV fingerprints on the host gene machinery and its regulation by microRNA holds a great promise and potential for improving our understanding of HAD pathogenesis, its diagnosis and therapy.

RESULTS

A parallel profiling of mRNA and miRNA of the frontal cortex autopsies from HIV positive patients with and without dementia was performed using Illumina Human-6 BeadChip and Affymetrix version 1.0 miRNA array, respectively. The gene ontology and pathway analysis of the two data sets showed high concordance between miRNA and mRNAs, revealing significant interference with the host axon guidance and its downstream signalling pathways in HAD brains. Moreover, the differentially expressed (DE) miRNAs identified in this study, in particular miR-137, 153 and 218, based on which most correlations were built cumulatively targeted neurodegeneration related pathways, implying their future potential in diagnosis, prognosis and possible therapies for HIV-mediated and possibly other neurodegenerative diseases. Furthermore, this relationship between DE miRNAs and DE mRNAs was also reflected in correlation analysis using Bayesian networks by splitting-averaging strategy (SA-BNs), which revealed 195 statistically significant correlated miRNA-mRNA pairs according to Pearson's correlation test (P<0.05).

CONCLUSIONS

Our study provides the first evidence on unambiguous support for intrinsic functional relationship between mRNA and miRNA in the context of HIV-mediated neurodegeneration, which shows that neurologic manifestation in HIV patients possibly occurs through the interference with the host axon guidance and its downstream signalling pathways. These data provide an excellent avenue for the development of new generation of diagnostic/prognostic biomarkers and therapeutic intervention strategies for HIV-associated neurodegeneration.

Comparison of polysomnographic data in age-, sex- and Axis I psychiatric diagnosis matched HIV-seropositive and HIV-seronegative insomnia patients

OBJECTIVE

There is a high prevalence of insomnia in HIV-seropositive patients. Insomnia is associated with poorer disease outcomes, cognitive impairment and HIV-associated dementia. However there is limited data characterizing the type of sleep disturbances, and the cause. Previous studies report conflicting results, and observed changes in the distribution of REM and SWS were hypothesized to result from co-morbid mood disorders, although this is not established. We carried out this study to determine if there are differences in polysomnographic (PSG) sleep data in age-, sex- and Axis I diagnoses- matched HIV-seropositive and HIV-seronegative patients.

METHODS

Eighteen HIV-seropositive insomniacs were matched to HIV-seronegative insomniacs based on age, sex and Axis I diagnoses. Participants spent 2 consecutive nights in a sleep lab recording of PSG data.

RESULTS

Multivariate analysis revealed an overall significant match-by-variable interaction (p=0.0126). Follow-up analysis show that compared to HIV-seronegative insomnia controls, HIV-seropositive insomniacs have significantly longer SOL, 8% decreased sleep efficiency, and 8-10% decreased time spent in REM sleep (p's<0.05).

CONCLUSION

This study provides preliminary evidence that even after accounting for differences in age, sex and psychiatric diagnoses, HIV-seropositive patients with insomnia have significantly worse sleep than HIV-seronegative patients with insomnia.

SIGNIFICANCE

Unlike what previous authors have proposed, our results do not support the view that comorbid psychiatric disorders like depression are responsible for the observed differences in PSG findings and the greater incidence of insomnia, in HIV-seropositive patients when compared with other groups of insomnia patients. This suggests the presence of other etiologies including neuronal damage, psychosocial stressors, or comorbid medical conditions. Further studies are needed to determine the extent to which these play a role in insomnia in the HIV-seropositive population.

Independent effects of HIV, aging, and HAART on brain volumetric measures

BACKGROUND

Neurocognitive impairment remains prevalent in HIV-infected (HIV+) individuals despite highly active antiretroviral therapy (HAART). We assessed the impact of HIV, HAART, and aging using structural neuroimaging.

METHODS

Seventy-eight participants [HIV- (n = 26), HIV+ on stable HAART (HIV+/HAART+; n = 26), HIV+ naive to HAART (HIV+/HAART-; n = 26)] completed neuroimaging and neuropsychological testing. A subset of HIV+ subjects (n = 12) performed longitudinal assessments before and after initiating HAART. Neuropsychological tests evaluated memory, psychomotor speed, and executive function, and a composite neuropsychological score was calculated based on normalized performances (neuropsychological summary Z score, NPZ-4). Volumetrics were evaluated for the amygdala, caudate, thalamus, hippocampus, putamen, corpus callosum, and cerebral gray and white matter. A 3-group 1-way analysis of variance assessed differences in neuroimaging and neuropsychological indices. Correlations were examined between NPZ-4 and volumetrics. Exploratory testing using a broken-stick regression model evaluated self-reported duration of HIV infection on brain structure.

RESULTS

HIV+ individuals had significant reductions in brain volumetrics within select subcortical regions (amygdala, caudate, and corpus callosum) compared with HIV- participants. However, HAART did not affect brain structure as regional volumes were similar for HIV+/HAART- and HIV+/HAART+. No association existed between NPZ-4 and volumetrics. HIV and aging were independently associated with volumetric reductions. Exploratory analyses suggest caudate atrophy due to HIV slowly occurs after self-reported seroconversion.

CONCLUSIONS

HIV associated volumetric reductions within the amygdala, caudate, and corpus callosum occurs despite HAART. A gradual decline in caudate volume occurs after self-reported seroconversion. HIV and aging independently increase brain vulnerability. Additional longitudinal structural magnetic resonance imaging studies, especially within older HIV+ participants, are required.

The kynurenine pathway and quinolinic acid: pivotal roles in HIV associated neurocognitive disorders

This brief review will first consider HIV associated neurocognitive disorder followed by the current understanding of its neuropathogenesis. Against this background the role of the kynurenine pathway will be detailed. Evidence both direct and indirect will be discussed for involvement of the kynurenine pathway at each step in the neuropathogenesis of HIV associated neurocognitive disorder.

HIV-associated neurological disorders: a guide to pharmacotherapy

In the era of highly active antiretroviral therapy (HAART), HIV-1-associated neurocognitive disorder (HAND) continues to be a common and significant morbidity among individuals infected with HIV. The term HAND encompasses a spectrum of progressively severe CNS involvement, ranging from asymptomatic neurocognitive impairment and minor neurocognitive disorder through to the most severe form of HIV-associated dementia (HAD). While the incidence of HAD has declined significantly with HAART, the milder forms of HAND persist. In addition, HAND now develops in individuals with less advanced immunosuppression. The reasons for the persistence of milder forms of HAND in individuals treated with HAART are not entirely known. There are several hypotheses to explain this phenomenon that include the legacy effect, a failure of antiretroviral agents to reverse neurological damage, poor access of antiretroviral agents to the CNS, chronic systemic immune activation associated with microbial translocation products, sustained CNS inflammation, the improved survival of HIV-seropositive individuals and the possible contribution from aging, amyloid deposition and other co-morbidities. In contrast, the incidence of HIV-associated CNS opportunistic processes including progressive multifocal leukoencephalopathy, tuberculosis, CNS toxoplasmosis, cytomegalovirus encephalitis, cryptococcosis and primary CNS lymphoma has declined dramatically with the introduction of HAART. This review briefly summarizes our current understanding of HAND and the pathological mechanisms involved, namely direct injury from HIV-1 and viral proteins, indirect neurotoxicity from proinflammatory cytokines and chronic, sustained immune activation in the CNS. To date, only HAART has been shown to benefit HAND despite numerous controlled trials of adjunctive 'anti-inflammatory' agents. Although HAART has a profound impact on the incidence and severity of HAND, there exists a 'therapeutic gap' as even HAART that is effective at inducing durable virological suppression may only partially reverse HAND. In addition, there may be potential CNS adverse effects of antiretroviral agents. There is an ongoing multicentre clinical trial to investigate the role of the CNS Penetration-Effectiveness index, an indicator of drug permeability and availability in the CNS, to help guide the choice of antiretroviral agents in the treatment of HAND. With recent recommendations for earlier treatment intervention with HAART for HIV-1 infection, it remains to be seen the effects of this on HAND. There is an urgent need to better define the therapeutic guidelines for the prevention and treatment of HAND.

HIV-1 infection and cognitive impairment in the cART era: a review

With the introduction of combination antiretroviral therapy AIDS dementia complex or HIV-associated dementia, as it was termed later, largely disappeared in clinical practice. However, in the past few years, patients, long-term infected and treated, including those with systemically well controlled infection, started to complain about milder memory problems and slowness, difficulties in concentration, planning, and multitasking. Neuropsychological studies have confirmed that cognitive impairment occurs in a substantial (15-50%) proportion of patients. Among HIV-1-infected patients cognitive impairment was and is one of the most feared complications of HIV-1 infection. In addition, neurocognitive impairment may affect adherence to treatment and ultimately result in increased morbidity for systemic disease. So what may be going on in the CNS after so many years of apparently controlled HIV-1 infection is an urgent and important challenge in the field of HIV medicine. In this review we summarize the key currently available data. We describe the clinical neurological and neuropsychological findings, the preferred diagnostic approach with new imaging techniques and cerebrospinal fluid analysis. We try to integrate data on pathogenesis and finally discuss possible therapeutic interventions.

HIV coreceptor tropism in paired plasma, peripheral blood mononuclear cell, and cerebrospinal fluid isolates from antiretroviral-naïve subjects

A survey of HIV coreceptor usage in cerebrospinal fluid (CSF) samples, peripheral blood mononuclear cells (PBMCs), and plasma samples from naïve seropositive patients was conducted. One hundred patients were enrolled in this study. Of the 100 patients, 36 had a primary or recent infection (P-RI), 31 had an early chronic infection (>350 CD4 cells) (ECI), and 33 had a late chronic infection (LCI). All 3 compartments were sampled in a subset of 33 participants, while the remaining 67 patients provided plasma samples and PBMCs only. Seventy-seven patients harbored the R5 virus in plasma samples and had a significantly higher median and percentage of CD4(+) T cells than patients with X4 virus (437 and 281 cells/μl, respectively; P = 0.0086; 20.6% and 18.6%, respectively). The X4 strain was detected more frequently in patients with LCI than in patients with P-RI or ECI (39.3%, 19.4%, and 9.6%, respectively; P = 0.0063). PBMC and plasma tropism was concordant in 90 patients, and 73 had the R5 strain. Among patients with discordant results, 4 had the R5 virus in their plasma and the X4 virus in PBMCs; 6 showed the opposite profile. Plasma, PBMC, and CSF tropism determinations were concordant in 26/33 patients (21 patients had R5, and 5 had X4). The tropism was discordant in 5/33 patients, with the X4 virus in plasma and R5 in CSF; the HIV tropism in PBMCs was X4 in 3 patients. The remaining 2/33 patients had the R5 virus in plasma and PBMCs and the X4 virus in CSF; one of these patients had a P-RI. The discordant tropism in CSF and blood may have implications for chemokine (C-C motif) receptor 5 (CCR5) antagonist use in patients with limited response to antiretroviral therapy (ART) or in responding patients evaluated for simplification of treatment.

The role of medical imaging in defining CNS abnormalities associated with HIV-infection and opportunistic infections

In this review of the current literature, we examine the role of medical imaging in providing new and relevant information on central nervous system (CNS) injury associated with human immunodeficiency virus (HIV) infection and various clinical manifestations of this injury. Common imaging modalities used to examine CNS injury in HIV infection include structural magnetic resonance imaging, magnetic resonance spectroscopy, diffusion tensor imaging, functional MRI, and positron emissions tomography. Clinical implications for the findings are discussed for each of these modalities individually and collectively. In addition, the direction for future studies is suggested in an attempt to provide possible methods that might answer the many questions that remain to be answered on the evolution and progression of CNS injury in the context of HIV infection.

Cerebral metabolite abnormalities in human immunodeficiency virus are associated with cortical and subcortical volumes

Cerebral metabolite disturbances occur among human immunodeficiency virus (HIV)-infected people, and are thought to reflect neuropathology, including proinflammatory processes, and neuronal loss. HIV-associated cortical atrophy continues to occur, though its basis is not well understood, and the relationship of cerebral metabolic disturbance to structural brain abnormalities in HIV has not been well delineated. We hypothesized that metabolite disturbances would be associated with reduced cortical and subcortical volumes. Cerebral volumes were measured in 67 HIV-infected people, including 10 people with mild dementia (acquired immunodeficiency syndrome [AIDS] dimentia complex [ADC] stage >1) via automated magnetic resonance imaging (MRI) segmentation. Magnetic resonance spectroscopy (MRS) was used to measure levels of cerebral metabolites N-acetylaspartate (NAA), myo-inositol (MI), choline-containing compounds (Cho), glutamate/glutamine (Glx), and creatine (Cr) from three brain regions (frontal gray matter, frontal white matter, basal ganglia). Analyses were conducted to examine the associations between MRS and cerebral volumetric measures using both absolute and relative metabolite concentrations. NAA in the mid-frontal gray matter was most consistently associated with cortical (global, frontal, and parietal), ventricular, and caudate volumes based on analysis of absolute metabolite levels, whereas temporal lobe volume was associated with basal ganglia NAA and Glx, and Cho concentrations in the frontal cortex and basal ganglia. Hippocampal volume was associated with frontal white matter NAA, whereas thalamic volume was associated with both frontal white matter NAA and basal ganglia Glx. Analyses of relative metabolite concentrations (referenced to Cr) yielded weaker effects, although more metabolites were retained as significant predictors in the models than the analysis of absolute concentrations. These findings demonstrate that reduced cortical and subcortical volumes, which have been previously found to be linked to HIV status and history, are also strongly associated with the degree of cerebral metabolite disturbance observed via MRS. Reduced cortical and hippocampal volumes were most strongly associated with decreased NAA, though reduced Glx also tended to be associated with reduced cortical and subcortical volumes (caudate and thalamus) as well, suggesting both neuronal and glial disturbances. Interestingly, metabolite-volumetric relationships were not limited to the cortical region from which MRS was measured, possibly reflecting shared pathophysiological processes. The relationships between Cho and volumetric measures suggest a complicated relationship possibly related to the effects of inflammatory processes on brain volume. The findings demonstrate the relationship between MRI-derived measures of cerebral metabolite disturbances and structural brain integrity, which has implication in understanding HIV-associated neuropathological mechanisms.

Maraviroc-containing regimen suppresses HIV replication in the cerebrospinal fluid of patients with neurological symptoms

We report the concentrations of maraviroc in the cerebrospinal fluid (CSF) and plasma of six HIV-1-infected patients with both neurological impairment and detectable HIV-1 replication in CSF. One month after starting maraviroc, the viral load in the CSF decreased significantly (P = 0.005). The median (range) maraviroc concentration in plasma was 347 ng/ml (123-2678). Four patients had CSF concentrations above the protein-adjusted inhibitory concentration (IC90) of 0.57 ng/ml (0.06-10.7) with a median of 102 ng/ml (35-173).

HIV reservoirs in vivo and new strategies for possible eradication of HIV from the reservoir sites

Even though the treatment of human immunodeficiency virus (HIV)-infected individuals with highly active antiretroviral therapy (HAART) provides a complete control of plasma viremia to below detectable levels (<40 copies/mL plasma), there is an unequal distribution of all antiretroviral drugs across diverse cellular and anatomic compartments in vivo. The main consequence of this is the acquisition of resistance by HIV to all known classes of currently prescribed antiretroviral drugs and the establishment of HIV reservoirs in vivo. HIV has a distinct advantage of surviving in the host via both pre-and postintegration latency. The postintegration latency is caused by inert and metabolically inactive provirus, which cannot be accessed either by the immune system or the therapeutics. This integrated provirus provides HIV with a safe haven in the host where it is incessantly challenged by its immune selection pressure and also by HAART. Thus, the provirus is one of the strategies for viral concealment in the host and the provirus can be rekindled, through unknown stimuli, to create progeny for productive infection of the host. Thus, the reservoir establishment remains the biggest impediment to HIV eradication from the host. This review provides an overview of HIV reservoir sites and discusses both the virtues and problems associated with therapies/strategies targeting these reservoir sites in vivo.

Tryptophan, Neurodegeneration and HIV-Associated Neurocognitive Disorder

This review presents an up-to-date assessment of the role of the tryptophan metabolic and catabolic pathways in neurodegenerative disease and HIV-associated neurocognitive disorder. The kynurenine pathway and the effects of each of its enzymes and products are reviewed. The differential expression of the kynurenine pathway in cells within the brain, including inflammatory cells, is explored given the increasing recognition of the importance of inflammation in neurodegenerative disease. An overview of common mechanisms of neurodegeneration is presented before a review and discussion of the evidence for a pathogenetic role of the kynurenine pathway in Alzheimer's disease, HIV-associated neurocognitive disorder, Huntington's disease, motor neurone disease, and Parkinson's disease.

Does acute hepatitis C infection affect the central nervous system in HIV-1 infected individuals?

Central nervous system (CNS) manifestations of chronic hepatitis C virus (HCV) and chronic human immune deficiency virus-1 (HIV-1) infections have been reported, but the impact of acute HCV infection on the CNS is unknown. A total of 10 individuals with chronic stable HIV-1 with documented acute HCV (HCV-RNA polymerase chain reaction positive and HCV antibody negative, group 1) underwent cerebral proton magnetic resonance spectroscopy (MRS) using acquisition parameters to quantify myo-inositol/creatine (mI/Cr) ratio in the right basal ganglia (RBG). Two matched control groups also underwent MRS; group 2: ten with chronic HIV-1 and no evidence of HCV, and group 3: ten with no evidence of HIV or HCV. Subjects also underwent computerized neurocognitive assessments (CogState). RBG mI/Cr ratio in group 1 (acute HCV in a background of HIV) was significantly lower than that in groups 2 and 3 [2.90 (+/-0.7) vs 3.34 (+/-0.4) and 3.43 (+/-0.4), mean (SD) for group 1 vs 2 and 3 respectively, P = 0.049], with 50% of subjects in group 1 having a mI/Cr ratio below the lowest observed ratio in either of the other groups. On neurocognitive testing, significant defects in the monitoring domain were observed in group-1, compared with matched controls (P = 0.021). Acute HCV in HIV-1 infected subjects is associated with CNS involvement. Clinicians should be vigilant of early CNS involvement when assessing subjects with acute HCV.

Amyloid and tau cerebrospinal fluid biomarkers in HIV infection

Background

Because of the emerging intersections of HIV infection and Alzheimer's disease, we examined cerebrospinal fluid (CSF) biomarkers related of amyloid and tau metabolism in HIV-infected patients.

Methods

In this cross-sectional study we measured soluble amyloid precursor proteins alpha and beta (sAPPα and sAPPβ), amyloid beta fragment 1-42 (Aβ_1-42), and total and hyperphosphorylated tau (t-tau and p-tau) in CSF of 86 HIV-infected (HIV+) subjects, including 21 with AIDS dementia complex (ADC), 25 with central nervous system (CNS) opportunistic infections and 40 without neurological symptoms and signs. We also measured these CSF biomarkers in 64 uninfected (HIV-) subjects, including 21 with Alzheimer's disease, and both younger and older controls without neurological disease.

Results

CSF sAPPα and sAPPβ concentrations were highly correlated and reduced in patients with ADC and opportunistic infections compared to the other groups. The opportunistic infection group but not the ADC patients had lower CSF Aβ_1-42 in comparison to the other HIV+ subjects. CSF t-tau levels were high in some ADC patients, but did not differ significantly from the HIV+ neuroasymptomatic group, while CSF p-tau was not increased in any of the HIV+ groups. Together, CSF amyloid and tau markers segregated the ADC patients from both HIV+ and HIV- neuroasymptomatics and from Alzheimer's disease patients, but not from those with opportunistic infections.

Conclusions

Parallel reductions of CSF sAPPα and sAPPβ in ADC and CNS opportunistic infections suggest an effect of CNS immune activation or inflammation on neuronal amyloid synthesis or processing. Elevation of CSF t-tau in some ADC and CNS infection patients without concomitant increase in p-tau indicates neural injury without preferential accumulation of hyperphosphorylated tau as found in Alzheimer's disease. These biomarker changes define pathogenetic pathways to brain injury in ADC that differ from those of Alzheimer's disease.

Evidence for predilection of macrophage infiltration patterns in the deeper midline and mesial temporal structures of the brain uniquely in patients with HIV-associated dementia

Background

HIV-1 penetrates the central nervous system, which is vital for HIV-associated dementia (HAD). But the role of cellular infiltration and activation together with HIV in the development of HAD is poorly understood.

Methods

To study activation and infiltration patterns of macrophages, CD8+ T cells in relation to HIV in diverse CNS areas of patients with and without dementia. 46 brain regions from two rapidly progressing severely demented patients and 53 regions from 4 HIV+ non-dementia patients were analyzed. Macrophage and CD8+ T cell infiltration of the CNS in relation to HIV was assessed using immuno-histochemical analysis with anti-HIV (P24), anti-CD8 and anti-CD68, anti-S-100A8 and granzyme B antibodies (cellular activation). Statistical analysis was performed with SPSS 12.0 with Student's t test and ANOVA.

Results

Overall, the patterns of infiltration of macrophages and CD8+ T cells were indiscernible between patients with and without dementia, but the co-localization of macrophages and CD8+ T cells along with HIV P24 antigen in the deeper midline and mesial temporal structures of the brain segregated the two groups. This predilection of infected macrophages and CD8+ T cells to the middle part of the brain was unique to both HAD patients, along with unique nature of provirus gag gene sequences derived from macrophages in the midline and mesial temporal structures.

Conclusion

Strong predilection of infected macrophages and CD8+ T cells was typical of the deeper midline and mesial temporal structures uniquely in HAD patients, which has some influence on neurocognitive impairment during HIV infection.

Neurodegenerative disorders and nanoformulated drug development

Degenerative and inflammatory diseases of the CNS include, but are not limited to, Alzheimer's and Parkinson's disease, amyotrophic lateral sclerosis, stroke, multiple sclerosis and HIV-1-associated neurocognitive disorders. These are common, debilitating and, unfortunately, hold few therapeutic options. In recent years, the application of nanotechnologies as commonly used or developing medicines has served to improve pharmacokinetics and drug delivery specifically to CNS-diseased areas. In addition, nanomedical advances are leading to therapies that target CNS pathobiology and as such, can interrupt disordered protein aggregation, deliver functional neuroprotective proteins and alter the oxidant state of affected neural tissues. This article focuses on the pathobiology of common neurodegenerative disorders with a view towards how nanomedicine may be used to improve the clinical course of neurodegenerative disorders.

Clinical implications of antiretroviral pharmacokinetics and pharmacodynamics in the CNS

The prevalence of HIV-associated brain disease remains high in the combination antiretroviral era. Factors associated with the development of HIV-associated neurocognitive impairment remain poorly understood. The selection of an antiretroviral regimen that can successfully penetrate the CNS compartment and control cerebrospinal fluid HIV replication may prove a crucial strategy in preventing the emergence and progression of HIV-associated neurocognitive impairment. Different antiretroviral agents and drug classes vary in their ability to penetrate the CNS. In this review, data on the CNS penetration of antiretrovirals are evaluated, including the clinical studies examining their relevance. Prospective studies examining the effect of different treatment strategies on CNS clinical outcomes are needed.