Confound, Cause, or Cure: The Effect of Cannabinoids on HIV-Associated Neurological Sequelae

The persistence of human immunodeficiency virus-1 (HIV)-associated neurocognitive disorders (HAND) in the era of effective antiretroviral therapy suggests that modern HIV neuropathogenesis is driven, at least in part, by mechanisms distinct from the viral life cycle. Identifying more subtle mechanisms is complicated by frequent comorbidities in HIV⁺ populations. One of the common confounds is substance abuse, with cannabis being the most frequently used psychoactive substance among people living with HIV. The psychoactive effects of cannabis use can themselves mimic, and perhaps magnify, the cognitive deficits observed in HAND; however, the neuromodulatory and anti-inflammatory properties of cannabinoids may counter HIV-induced excitotoxicity and neuroinflammation. Here, we review our understanding of the cross talk between HIV and cannabinoids in the central nervous system by exploring both clinical observations and evidence from preclinical in vivo and in vitro models. Additionally, we comment on recent advances in human, multi-cell in vitro systems that allow for more translatable, mechanistic studies of the relationship between cannabinoid pharmacology and this uniquely human virus.

IgG intrathecal synthesis in HIV-associated neurocognitive disorder (HAND) according to the HIV-1 subtypes and pattern of HIV RNA in CNS and plasma compartments

We hypothesized that humoral immunity stimulation in the CNS in HIV-1C patients would be lower than that in HIV-1B due to a defective Tat chemokine dimotif (C30C31) that might influence cellular trafficking and CNS inflammation. Sixty-eight paired CSF and blood samples from people with HIV (PWH), free of CNS opportunistic infections, were included, HIV-1B (n = 27), HIV-1C (n = 26), and HIV negative (n = 25). IgG intrathecal synthesis was assayed using quantitative and qualitative methods. IgG oligoclonal bands (OCB) in CSF were observed in 51% of PWH, comparable between HIV-1B and HIV-1C, as well as the medians of IgG intrathecal synthesis formulas. The group with HIV infection aviremic in CSF and blood showed 75% of OCB. There was a poor positive correlation between the IgG quotient and GDS. The impact of HIV-1 on IgG intrathecal production was not subtype dependent. Low-grade CNS intrathecal IgG production persists in HIV CNS infection even in PWH with CSF and blood HIV RNA controlled.

Effects of HIV gp120 on Neuroinflammation in Immunodeficient vs. Immunocompetent States

HIV affects 37 million people worldwide, 25-69% of which develop HIV-associated neurocognitive disorders (HAND) regardless of antiviral treatment. HIV infection of the brain decreases cognitive function, disrupts/impairs learning and memory, and reduces quality of life for those affected. HIV-induced neuroinflammation has been associated with viral proteins such as gp120 and Tat, which remain elevated in the CNS even in patients with low peripheral viremia counts. In this study, we examined the effects of gp120 on neuroinflammation in immunodeficient vs. immunocompetent states by examining neuroinflammatory markers in gp120tg mice with or without systemic immunodeficiency caused by murine retroviral administration (LP-BM5 murine AIDS). Changes in inflammatory cytokine/chemokine mRNA expression was complex and dependent upon expression of gp120 protein, immunodeficiency status, brain region (hippocampus, frontal lobe, or striatum), and age. Gp120 expression reduced hippocampal synaptophysin expression but did not affect animals' learning/memory on the spontaneous T-maze test in our experimental conditions. Our results emphasize the critical role of the neuroinflammatory micro-environment and the peripheral immune system context in which gp120 acts. Multiple factors, particularly system-level differences in the immune response of different brain regions, need to be considered when developing treatment for HAND. Graphical Abstract.

Emerging Role of Nef in the Development of HIV Associated Neurological Disorders

Despite adherence to treatment, individuals living with HIV have an increased risk for developing cognitive impairments, referred to as HIV-associated neurological disorders (HAND). Due to continued growth in the HIV population, particularly amongst the aging cohort, the neurobiological mechanisms of HAND are increasingly relevant. Similar to other viral proteins (e.g. Tat, Gp120, Vpr), the Negative Factor (Nef) is associated with numerous adverse effects in the CNS as well as cognitive impairments. In particular, emerging data indicate the consequences of Nef may be facilitated by the modulation of cellular autophagy as well as its inclusion into extracellular vesicles (EVs). The present review examines evidence for the molecular mechanisms by which Nef might contribute to neuronal dysfunction underlying HAND, with a specific focus on autophagy and EVs. Based on the these data, we propose an integrated model by which Nef may contribute to underlying neuronal dysfunction in HAND and highlight potentially novel therapeutic targets for HAND. Graphical abstract.

Microglial HIV-1 Expression: Role in HIV-1 Associated Neurocognitive Disorders

The persistence of HIV-1 viral reservoirs in the brain, despite treatment with combination antiretroviral therapy (cART), remains a critical roadblock for the development of a novel cure strategy for HIV-1. To enhance our understanding of viral reservoirs, two complementary studies were conducted to (1) evaluate the HIV-1 mRNA distribution pattern and major cell type expressing HIV-1 mRNA in the HIV-1 transgenic (Tg) rat, and (2) validate our findings by developing and critically testing a novel biological system to model active HIV-1 infection in the rat. First, a restricted, region-specific HIV-1 mRNA distribution pattern was observed in the HIV-1 Tg rat. Microglia were the predominant cell type expressing HIV-1 mRNA in the HIV-1 Tg rat. Second, we developed and critically tested a novel biological system to model key aspects of HIV-1 by infusing F344/N control rats with chimeric HIV (EcoHIV). In vitro, primary cultured microglia were treated with EcoHIV revealing prominent expression within 24 h of infection. In vivo, EcoHIV expression was observed seven days after stereotaxic injections. Following EcoHIV infection, microglia were the major cell type expressing HIV-1 mRNA, results that are consistent with observations in the HIV-1 Tg rat. Within eight weeks of infection, EcoHIV rats exhibited neurocognitive impairments and synaptic dysfunction, which may result from activation of the NogoA-NgR3/PirB-RhoA signaling pathway and/or neuroinflammation. Collectively, these studies enhance our understanding of HIV-1 viral reservoirs in the brain and offer a novel biological system to model HIV-associated neurocognitive disorders and associated comorbidities (i.e., drug abuse) in rats.

Moving on from HAND: why we need new criteria for cognitive impairment in people with HIV and a proposed way forward

HIV-associated neurocognitive disorders (HAND) criteria are frequently used to describe cognitive impairment in people with HIV (PWH) across diverse populations globally. These criteria typically find 20-60% of PWH meet criteria for HAND, which does not tally with clinical observations in the modern era that cognitive disorders present relatively infrequently. Most with HAND have asymptomatic neurocognitive impairment (ANI), however the significance of low cognitive test performance without symptoms is uncertain. Methods underlying HAND criteria carry a false positive rate that can exceed 20%. Comorbidities, education and complex socioeconomic factors can influence cognitive test performance, further increasing the potential for misclassification. We propose a new framework to characterise cognitive impairment in PWH which requires a clinical history and acknowledges the multifactorial nature of low cognitive test performance. This framework is intended to be applicable across diverse populations globally, be more aligned with clinical observations and more closely represent HIV brain pathology.

Reductions in Gray Matter Linked to Epigenetic HIV-Associated Accelerated Aging

A growing literature suggests a relationship between HIV-infection and a molecular profile of age acceleration. However, despite the widely known high prevalence of HIV-related brain atrophy and HIV-associated neurocognitive disorder (HAND), epigenetic age acceleration has not been linked to HIV-related changes in structural MRI. We applied morphological MRI methods to study the brain structure of 110 virally suppressed participants with HIV infection and 122 uninfected controls age 22-72. All participants were assessed for cognitive impairment, and blood samples were collected from a subset of 86 participants with HIV and 83 controls to estimate epigenetic age. We examined the group-level interactive effects of HIV and chronological age and then used individual estimations of epigenetic age to understand the relationship between age acceleration and brain structure. Finally, we studied the effects of HAND. HIV-infection was related to gray matter reductions, independent of age. However, using epigenetic age as a biomarker for age acceleration, individual HIV-related age acceleration was associated with reductions in total gray matter. HAND was associated with decreases in thalamic and hippocampal gray matter. In conclusion, despite viral suppression, accentuated gray matter loss is evident with HIV-infection, and greater biological age acceleration specifically relates to such gray matter loss.

HIV-1 and drug abuse comorbidity: Lessons learned from the animal models of NeuroHIV

Various research studies that have investigated the association between HIV infection and addiction underpin the role of various drugs of abuse in impairing immunological and non-immunological pathways of the host system, ultimately leading to augmentation of HIV infection and disease progression. These studies have included both in vitro and in vivo animal models wherein investigators have assessed the effects of various drugs on several disease parameters to decipher the impact of drugs on both HIV infection and progression of HIV-associated neurocognitive disorders (HAND). However, given the inherent limitations in the existing animal models of HAND, these investigations only recapitulated specific aspects of the disease but not the complex human syndrome. Despite the inability of HIV to infect rodents over the last 30 years, multiple strategies have been employed to develop several rodent models of HAND. While none of these models can accurately mimic the overall pathophysiology of HAND, they serve the purpose of modeling some unique aspects of HAND. This review provides an overview of various animal models used in the field and a careful evaluation of methodological strengths and limitations inherent in both the model systems and study designs to understand better how the various animal models complement one another.

Opioid Modulation of Neuronal Iron and Potential Contributions to NeuroHIV

Opioid use has substantially increased over recent years and remains a major driver of new HIV infections worldwide. Clinical studies indicate that opioids may exacerbate the symptoms of HIV-associated neurocognitive disorders (HAND), but the mechanisms underlying opioid-induced cognitive decline remain obscure. We recently reported that the μ-opioid agonist morphine increased neuronal iron levels and levels of ferritin proteins that store iron, suggesting that opioids modulate neuronal iron homeostasis. Additionally, increased iron and ferritin heavy chain protein were necessary for morphine's ability to reduce the density of thin and mushroom dendritic spines in cortical neurons, which are considered critical mediators of learning and memory, respectively. As altered iron homeostasis has been reported in HAND and related neurocognitive disorders like Alzheimer's, Parkinson's, and Huntington's disease, understanding how opioids regulate neuronal iron metabolism may help identify novel drug targets in HAND with potential relevance to these other neurocognitive disorders. Here, we review the known mechanisms of opioid-mediated regulation of neuronal iron and corresponding cellular responses and discuss the implications of these findings for patients with HAND. Furthermore, we discuss a new molecular approach that can be used to understand if opioid modulation of iron affects the expression and processing of amyloid precursor protein and the contributions of this pathway to HAND.

Mini-review: Elucidating the psychological, physical, and sex-based interactions between HIV infection and stress

Stress is generally classified as any mental or emotional strain resulting from difficult circumstances, and can manifest in the form of depression, anxiety, post-traumatic stress disorder (PTSD), or other neurocognitive disorders. Neurocognitive disorders such as depression, anxiety, and PTSD are large contributors to disability worldwide, and continue to affect individuals and communities. Although these disorders affect men and women, women are disproportionately represented among those diagnosed with affective disorders, a result of both societal gender roles and physical differences. Furthermore, the incidence of these neurocognitive disorders is augmented among People Living with HIV (PLWH); the physical ramifications of stress increase the likelihood of HIV acquisition, pathogenesis, and treatment, as both stress and HIV infection are characterized by chronic inflammation, which creates a more opportunistic environment for HIV. Although the stress response is facilitated by the autonomic nervous system (ANS) and the hypothalamic pituitary adrenal (HPA) axis, when the response involves a psychological component, additional brain regions are engaged. The impact of chronic stress exposure and the origin of individual variation in stress responses and resilience are at least in part attributable to regions outside the primary stress circuity, including the amygdala, prefrontal cortex, and hippocampus. This review aims to elucidate the relationship between stress and HIV, how these interact with sex, and to understand the physical ramifications of these interactions.

Beneficial and Adverse Effects of cART Affect Neurocognitive Function in HIV-1 Infection: Balancing Viral Suppression against Neuronal Stress and Injury

HIV-associated neurocognitive disorders (HAND) persist despite the successful introduction of combination antiretroviral therapy (cART). While insufficient concentration of certain antiretrovirals (ARV) may lead to incomplete viral suppression in the brain, many ARVs are found to cause neuropsychiatric adverse effects, indicating their penetration into the central nervous system (CNS). Several lines of evidence suggest shared critical roles of oxidative and endoplasmic reticulum stress, compromised neuronal energy homeostasis, and autophagy in the promotion of neuronal dysfunction associated with both HIV-1 infection and long-term cART or ARV use. As the lifespans of HIV patients are increased, unique challenges have surfaced. Longer lives convey prolonged exposure of the CNS to viral toxins, neurotoxic ARVs, polypharmacy with prescribed or illicit drug use, and age-related diseases. All of these factors can contribute to increased risks for the development of neuropsychiatric conditions and cognitive impairment, which can significantly impact patient well-being, cART adherence, and overall health outcome. Strategies to increase the penetration of cART into the brain to lower viral toxicity may detrimentally increase ARV neurotoxicity and neuropsychiatric adverse effects. As clinicians attempt to control peripheral viremia in an aging population of HIV-infected patients, they must navigate an increasingly complex myriad of comorbidities, pharmacogenetics, drug-drug interactions, and psychiatric and cognitive dysfunction. Here we review in comparison to the neuropathological effects of HIV-1 the available information on neuropsychiatric adverse effects and neurotoxicity of clinically used ARV and cART. It appears altogether that future cART aiming at controlling HIV-1 in the CNS and preventing HAND will require an intricate balancing act of suppressing viral replication while minimizing neurotoxicity, impairment of neurocognition, and neuropsychiatric adverse effects. Graphical abstract Schematic summary of the effects exerted on the brain and neurocognitive function by HIV-1 infection, comorbidities, psychostimulatory, illicit drugs, therapeutic drugs, such as antiretrovirals, the resulting polypharmacy and aging, as well as the potential interactions of all these factors.

Is There Any Evidence of Premature, Accentuated and Accelerated Aging Effects on Neurocognition in People Living with HIV? A Systematic Review

Despite evidence of premature, accentuated and accelerated aging for some age-related conditions such as cardiovascular diseases in people living with HIV (PLHIV), the evidence for these abnormal patterns of aging on neurocognition remains unclear. Further, no systematic review has been dedicated to this issue. Using PRISMA guidelines, we searched standard databases (PubMed, EMBASE, CINAHL and PsycINFO). Articles were included if they analyzed and reported the effect of age on neurocognition among PLHIV as one of their major findings, if they were conducted in the combination anti-retroviral therapy era (after 1996) and published in a peer-reviewed journal in English. Quality appraisal was conducted using the Joanna Briggs Institute (JBI) appraisal tools. To systematically target the abnormal patterns of neurocognitive aging, we define premature cognitive aging as significant interaction effect of HIV status and age on cross-sectional neurocognitive test performance covering both the normal and abnormal performance range; accentuated cognitive aging as significant interaction effect of HIV status and age on cross-sectional neurocognitive impairment (NCI) rate, thus covering the abnormal performance range only; accelerated cognitive aging as significant interaction effect of HIV status and age on longitudinal neurocognitive test performance or incidence of NCI. Because these definitions require an age-comparable HIV-negative (HIV-) control group, when no controls were included, we determined the range of the age effect on neurocognitive test performance or NCI among PLHIV. A total of 37 studies originating from the US (26), UK (2), Italy (2), Poland (2), China (2), Japan (1), Australia (1), and Brazil (1) were included. Six studies were longitudinal and 14 included HIV- controls. The quality appraisal showed that 12/37 studies neither used an age-matched HIV- controls nor used demographically corrected cognitive scores. A meta-analysis was not possible because study methods and choice of neurocognitive measurement methods and outcomes were heterogeneous imposing a narrative synthesis. In studies with an HIV- control sample, premature neurocognitive aging was found in 45% of the cross-sectional analyses (9/20), while accelerated neurocognitive aging was found in 75% of the longitudinal analyses (3/4). There was no evidence for accentuated aging, but this was tested only in two studies. In studies without an HIV- control sample, the age effect was always present but wide (NCI OR = 1.18-4.8). While large sample size (> 500) was associated with abnormal patterns of cognitive aging, most of the studies were under powered. Other study characteristics such as longitudinal study design and higher proportion of older participants were also associated with the findings of abnormal cognitive aging. There is some support for premature and accelerated cognitive aging among PLHIV in the existing literature especially among large and longitudinal studies and those with higher proportion of older samples. Future HIV and cognitive aging studies need to harmonize neuropsychological measurement methods and outcomes and use a large sample from collaborative multi-sites to generate more robust evidences.

CNS Neurotoxicity of Antiretrovirals

The development of novel antiretroviral treatments has led to a significant turning point in the fight against HIV. Although therapy leads to virologic suppression and prolonged life expectancies, HIV-associated neurocognitive disorder (HAND) remains prevalent. While various hypotheses have been proposed to explain this phenomenon, a growing body of literature explores the neurotoxic effects of antiretroviral therapy. Research to date brings into question the potential role of such medications in neurocognitive and neuropsychiatric impairment seen in HIV-positive patients. This review highlights recent findings and controversies in cellular, molecular, and clinical neurotoxicity of antiretrovirals. It explores the pathogenesis of such toxicity and relates it to clinical manifestations in each medication class. The concept of accelerated aging in persons living with HIV (PLWH) as well as potential treatments for HAND are also discussed. Ultimately, this article hopes to educate clinicians and basic scientists about the neurotoxic effects of antiretrovirals and spur future scientific investigation into this important topic. Graphical Abstract.

Mechanisms of neuronal dysfunction in HIV-associated neurocognitive disorders

HIV-associated neurocognitive disorder (HAND) is characterized by cognitive and behavioral deficits in people living with HIV. HAND is still common in patients that take antiretroviral therapies, although they tend to present with less severe symptoms. The continued prevalence of HAND in treated patients is a major therapeutic challenge, as even minor cognitive impairment decreases patient’s quality of life. Therefore, modern HAND research aims to broaden our understanding of the mechanisms that drive cognitive impairment in people with HIV and identify promising molecular pathways and targets that could be exploited therapeutically. Recent studies suggest that HAND in treated patients is at least partially induced by subtle synaptodendritic damage and disruption of neuronal networks in brain areas that mediate learning, memory, and executive functions. Although the causes of subtle neuronal dysfunction are varied, reversing synaptodendritic damage in animal models restores cognitive function and thus highlights a promising therapeutic approach. In this review, we examine evidence of synaptodendritic damage and disrupted neuronal connectivity in HAND from clinical neuroimaging and neuropathology studies and discuss studies in HAND models that define structural and functional impairment of neurotransmission. Then, we report molecular pathways, mechanisms, and comorbidities involved in this neuronal dysfunction, discuss new approaches to reverse neuronal damage, and highlight current gaps in knowledge. Continued research on the manifestation and mechanisms of synaptic injury and network dysfunction in HAND patients and experimental models will be critical if we are to develop safe and effective therapies that reverse subtle neuropathology and cognitive impairment.

Proteomics and metabolomics of HIV-associated neurocognitive disorders: A systematic review

HIV-associated neurocognitive disorders (HAND) are common features of the effect of human immunodeficiency virus (HIV)-1 within the central nervous system (CNS). The underlying neuropathophysiology of HAND is incompletely known. Furthermore, there are no markers to effectively predict or stratify the risk of HAND. Recent advancements in the fields of proteomics and metabolomics have shown promise in addressing these concerns, however, it is not clear if these approaches may provide new insight into pathways and markers related to HAND. We therefore conducted a systematic review of studies using proteomic and/or metabolomic approaches in the aim of identifying pathways or markers associated with neurocognitive impairment in people living with HIV (PLWH). Thirteen studies were eligible, including 11 proteomic and 2 metabolomic investigations of HIV-positive clinical samples (cerebrospinal fluid (CSF), brain tissue, and serum). Across varying profiling techniques and sample types, the majority of studies found an association of markers with neurocognitive function in PLWH. These included metabolic marker myo-inositol and proteomic markers superoxide dismutase, gelsolin, afamin, sphingomyelin, and ceramide. Certain markers were found to be dysregulated across various sample types. Afamin and gelsolin overlapped in studies of blood and CSF and sphingomyelin and ceramide overlapped in studies of CSF and brain tissue. The association of these markers with neurocognitive functioning may indicate the activity of certain pathways, potentially those related to the underlying neuropathophysiology of HAND.

The Increase of HIV-1 Infection, Neurocognitive Impairment, and Type 2 Diabetes in The Rio Grande Valley

The Human Immunodeficiency Virus (HIV-1) infection remains a persistent predicament for the State of Texas, ranking seventh among the most documented HIV cases in the United States. In this regard, the Rio Grande Valley (RGV) in South Texas is considered as one of the least investigated areas of the state with respect to HIV infection and HIV associated comorbidities. Considering the 115% increase in average HIV incidence rates per 100,000 within the RGV from 2007-2015, it is worth characterizing this population with respect to their HIV-1 infection, HIV-1 Associated Neurocognitive Disorders (HAND), and the association of treatment with combined antiretroviral therapy (cART). Moreover, the increased rate of Type-2 Diabetes (T2D) in the RGV population is intertwined with that of HIV-1 infection facing challenges due to the lack of knowledge about prevention to inadequate access to healthcare. Hence, the role of T2D in the development of HAND among the people living with HIV (PLWH) in the RGV will be reviewed to establish a closer link between T2D and HAND in cART-treated patients of the RGV.

Distinguishing Amnestic Mild Cognitive Impairment From HIV-Associated Neurocognitive Disorders

BACKGROUND

Memory impairment occurs in human immunodeficiency virus (HIV)-associated neurocognitive disorders (HAND) and amnestic mild cognitive impairment (aMCI), the precursor to Alzheimer disease (AD). Methods are needed to distinguish aMCI-associated from HAND-associated impairment in people with HIV (PWH). We developed a neuropsychological method of identifying aMCI in PWH and tested this by relating AD neuropathology (β-amyloid, phospho-Tau) to aMCI versus HAND classification.

METHODS

Seventy-four HIV-positive cases (aged 50-68 years) from the National NeuroAIDS Tissue Consortium had neurocognitive data within 1 year of death and data on β-amyloid and phospho-Tau pathology in frontal brain tissue. High aMCI risk was defined as impairment (<1.0 SD below normative mean) on 2 of 4 delayed recall or recognition outcomes from a verbal and nonverbal memory test (at least 1 recognition impairment required). Differences in β-amyloid and phospho-Tau by aMCI and HAND classification were examined.

RESULTS

High aMCI risk was more common in HAND (69.0%) versus no HAND (37.5%) group. β-amyloid pathology was 4.75 times more likely in high versus low aMCI risk group. Phospho-Tau pathology did not differ between aMCI groups. Neither neuropathological feature differed by HAND status.

CONCLUSIONS

Amnestic mild cognitive impairment criteria that include recognition impairment may help to detect AD-like cognitive/biomarker profiles among PWH.

Functional impact of HIV-1 Tat on cells of the CNS and its role in HAND

Human immunodeficiency virus type 1 (HIV-1) transactivator of transcription (Tat) is a potent mediator involved in the development of HIV-1-associated neurocognitive disorders (HAND). Tat is expressed even in the presence of antiretroviral therapy (ART) and is able to enter the central nervous system (CNS) through a variety of ways, where Tat can interact with microglia, astrocytes, brain microvascular endothelial cells, and neurons. The presence of low concentrations of extracellular Tat alone has been shown to lead to dysregulated gene expression, chronic cell activation, inflammation, neurotoxicity, and structural damage in the brain. The reported effects of Tat are dependent in part on the specific HIV-1 subtype and amino acid length of Tat used. HIV-1 subtype B Tat is the most common subtype in North American and therefore, most studies have been focused on subtype B Tat; however, studies have shown many genetic, biologic, and pathologic differences between HIV subtype B and subtype C Tat. This review will focus primarily on subtype B Tat where the full-length protein is 101 amino acids, but will also consider variants of Tat, such as Tat 72 and Tat 86, that have been reported to exhibit a number of distinctive activities with respect to mediating CNS damage and neurotoxicity.

Alzheimer's disease-like perturbations in HIV-mediated neuronal dysfunctions: understanding mechanisms and developing therapeutic strategies

Excessive exposure to toxic substances or chemicals in the environment and various pathogens, including viruses and bacteria, is associated with the onset of numerous brain abnormalities. Among them, pathogens, specifically viruses, elicit persistent inflammation that plays a major role in Alzheimer's disease (AD) as well as dementia. AD is the most common brain disorder that affects thought, speech, memory and ability to execute daily routines. It is also manifested by progressive synaptic impairment and neurodegeneration, which eventually leads to dementia following the accumulation of Aβ and hyperphosphorylated Tau. Numerous factors contribute to the pathogenesis of AD, including neuroinflammation associated with pathogens, and specifically viruses. The human immunodeficiency virus (HIV) is often linked with HIV-associated neurocognitive disorders (HAND) following permeation through the blood-brain barrier (BBB) and induction of persistent neuroinflammation. Further, HIV infections also exhibited the ability to modulate numerous AD-associated factors such as BBB regulators, members of stress-related pathways as well as the amyloid and Tau pathways that lead to the formation of amyloid plaques or neurofibrillary tangles accumulation. Studies regarding the role of HIV in HAND and AD are still in infancy, and potential link or mechanism between both is not yet established. Thus, in the present article, we attempt to discuss various molecular mechanisms that contribute to the basic understanding of the role of HIV-associated neuroinflammation in AD and HAND. Further, using numerous growth factors and drugs, we also present possible therapeutic strategies to curb the neuroinflammatory changes and its associated sequels.

Glycogen synthase kinase-3 inhibition rescues sex-dependent contextual fear memory deficit in human immunodeficiency virus-1 transgenic mice

BACKGROUND AND PURPOSE

A significant number of HIV-1 patients on antiretroviral therapy develop HIV-associated neurocognitive disorders (HAND). Evidence indicate that biological sex may regulate HAND pathogenesis, but the mechanisms remain unknown. We investigated synaptic mechanisms associated with sex differences in HAND, using the HIV-1-transgenic 26 (Tg26) mouse model.

EXPERIMENTAL APPROACH

Contextual- and cue-dependent memories of male and female Tg26 mice and littermate wild type mice were assessed in a fear conditioning paradigm. Hippocampal electrophysiology, immunohistochemistry, western blot, qRT-PCR and ELISA techniques were used to investigate cellular, synaptic and molecular impairments.

KEY RESULTS

Cue-dependent memory was unaltered in male and female Tg26 mice, when compared to wild type mice. Male, but not female, Tg26 mice showed deficits in contextual fear memory. Consistently, only male Tg26 mice showed depressed hippocampal basal synaptic transmission and impaired LTP induction in area CA1. These deficits in male Tg26 mice were independent of hippocampal neuronal loss and microglial activation but were associated with increased HIV-1 long terminal repeat mRNA expression, reduced hippocampal synapsin-1 protein, reduced BDNF mRNA and protein, reduced AMPA glutamate receptor (GluA1) phosphorylation levels and increased glycogen synthase kinase 3 (GSK3) activity. Importantly, selective GSK3 inhibition using 4-benzyl-2-methyl-1,2,4-thiadiazolidine-3,5-dione increased levels of synapsin-1, BDNF and phosphorylated-GluA1 proteins, restored hippocampal basal synaptic transmission and LTP, and improved contextual fear memory in male Tg26 mice.

CONCLUSION AND IMPLICATIONS

Sex-dependent impairments in contextual fear memory and synaptic plasticity in Tg26 mice are associated with increased GSK3 activity. This implicates GSK3 inhibition as a potential therapeutic strategy to improve cognition in HIV-1 patients.

Meta-analysis of brain metabolite differences in HIV infection

BACKGROUND

Numerous studies have used magnetic resonance spectroscopy (MRS) neurometabolite measurements to study HIV infection effects. While many have reported differences in total N-Acetylaspartate (tNAA), myo-Inositol (mI), and total Choline (tCho), there have been no meta-analyses performed to evaluate concordance across studies.

PURPOSE

To evaluate the consistency of HIV serostatus effects on brain metabolites.

STUDY SELECTION

The sample included studies conducted between 1993 and 2019 reporting HIV infection effects measured using proton MRS. tNAA/tCr ratios (21 papers), tCho/tCr ratios (21 papers), mI/tCr ratios (17 papers) and quantitative tCr (9 papers), sampling from basal ganglia (BG), gray matter (GM), and white matter (WM) were included.

DATA ANALYSIS

Random effects meta-analysis using inverse variance weighting and bias corrected standardized mean differences (SMDs) was used. Meta-regression examined effects of publication year and data acquisition technique differences.

DATA SYNTHESIS

BG SMDs related to positive serostatus were -0.10 [-0.39; 0.18] tNAA/tCr, 0.27 [0.05; 0.49] tCho/tCr, 0.60 [0.31; 0.90] mI/tCr, and -0.26 [-0.59; 0.06] tCr. GM SMDs related to serostatus were -0.29 [-0.49; -0.09] tNAA/tCr, 0.37 [0.19; 0.54] tCho/tCr, 0.41 [0.15; 0.68] mI/tCr, and -0.24 [-0.45; -0.03] tCr. WM SMDs related to serostatus were -0.52 [-0.79; -0.25] tNAA/tCr, 0.41 [0.21; 0.61] tCho/tCr, 0.59 [0.24; 0.94] mI/tCr, and -0.03 [-0.25; 0.19] tCr. WM regions showed larger serostatus effect sizes than BG and GM. I² ranged from 52 to 88% for the metabolite ratios. Both GM and WM tNAA/tCr SMDs were lower with increasing calendar year.

LIMITATIONS

Many studies pooled participants with varying treatment, infection, and comorbidity durations.

CONCLUSIONS

HIV neurometabolite studies showed consistently lower tNAA/tCr, higher tCho/tCr and higher mI/tCr ratios associated with chronic HIV infection. Substantial between-study variation may have resulted from measurement technique variations, study population differences and HIV treatment changes over time. Higher WM tCho/tCr and mI/tCr may reflect reactive gliosis or myelin turnover. Neurometabolite measurements can reliably detect chronic HIV infection effects and may be useful in understanding the pathophysiology of cognitive and sensorimotor decline following HIV infection.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence of neurometabolite differences in chronic HIV infection.

Novel method to quantify phenotypic markers of HIV-associated neurocognitive disorder in a murine SCID model

Despite combined antiretroviral therapy (cART), HIV infection in the CNS persists with reported increases in activation of macrophages (MΦ), microglia, and surrounding astrocytes/neurons, conferring HIV-induced inflammation. Chronic inflammation results in HIV-associated neurocognitive disorders (HAND) with reported occurrence of up to half of individuals with HIV infection. The existing HAND mouse model used by laboratories including ours, and the effect of novel agents on its pathology present with labor-intensive and time-consuming limitations since brain sections and immunohistochemistry assays have to be performed and analyzed. A novel flow cytometry-based system to objectively quantify phenotypic effects of HIV using a SCID mouse HAND model was developed which demonstrated that the HIV-infected mice had significant increases in astrogliosis, loss of neuronal dendritic marker, activation of murine microglia, and human macrophage explants compared to uninfected control mice. HIV p24 could also be quantified in the brains of the infected mice. Correlation of these impairments with HIV-induced brain inflammation and previous behavioral abnormalities studies in mice suggests that this model can be used as a fast and relevant throughput methodology to quantify preclinical testing of novel treatments for HAND.

Differential effects of integrase strand transfer inhibitors, elvitegravir and raltegravir, on oligodendrocyte maturation: A role for the integrated stress response

Regardless of adherence to combined antiretroviral therapy, white matter and myelin pathologies persist in patients with HIV-associated neurocognitive disorders, a spectrum of cognitive, motor, and behavioral impairments. We hypothesized that antiretroviral therapy alters the maturation of oligodendrocytes which synthesize myelin. We tested whether specific frontline integrase strand transfer inhibitors would alter oligodendrocyte differentiation and myelination. To model the effect of antiretrovirals on oligodendrocytes, we stimulated primary rat oligodendrocyte precursor cells to differentiate into mature oligodendrocytes in vitro in the presence of therapeutically relevant concentrations of elvitegravir or raltegravir and then assessed differentiation with lineage specific markers. To examine the effect of antiretrovirals on myelination, we treated mice with the demyelinating compound cuprizone, for 5 weeks. This was followed by 3 weeks of recovery in absence of cuprizone, during which time some mice received a daily intrajugular injection of elvitegravir. Brains were harvested, sectioned and processed by immunohistochemistry to examine oligodendrocyte maturation and myelination. Elvitegravir inhibited oligodendrocyte differentiation in vitro in a concentration-dependent manner, while raltegravir had no effect. Following cuprizone demyelination, administration of elvitegravir to adult mice reduced remyelination compared with control animals. Elvitegravir treatment activated the integrated stress response in oligodendrocytes in vitro, an effect which was completely blocked by pretreatment with the integrated stress response inhibitor Trans-ISRIB, preventing elvitegravir-mediated inhibition of oligodendrocyte maturation. These studies demonstrate that elvitegravir impairs oligodendrocyte maturation and remyelination and that the integrated stress response mediates this effect and may be a possible therapeutic target.

Peripheral immune dysregulation in the ART era of HIV-associated neurocognitive impairments: A systematic review

Human immunodeficiency virus-associated neurocognitive impairment (HANI) remains problematic despite the effective use of antiretroviral therapy (ART) and viral suppression. A dysregulated immune response contributes to the development of HANI but findings on the association between peripheral blood immune markers and HANI have been inconsistent. We therefore conducted a systematic review of studies of the association of peripheral blood immune markers with neurocognitive performance in ART experienced HIV-positive participants. Thirty-seven studies were eligible, including 12 longitudinal studies and 25 cross-sectional studies. Findings consistently show that HIV-positive participants have altered immune marker levels, including elevated markers of monocyte activation (neopterin, sCD14, sCD163) and inflammation (CCL2, IL-8, IL-18, IP-10, IFN-α, sTNFR-II and TNF-α). These elevated levels persist in HIV-positive participants despite ART. The majority of studies found associations of HANI with immune markers, including those linked to monocyte activation (sCD14 and sCD163) and inflammation (IL-18 and IP-10). Despite the heterogeneity of studies reviewed, due to the presence of raised peripheral markers, our narrative review provides evidence of chronic inflammation despite ART. The raised levels of these markers may suggest certain mechanisms are active, potentially those involved in the neuropathophysiology of HANI.

Peripheral blood lymphocyte proviral DNA predicts neurocognitive impairment in clade C HIV

It is not known if proviral DNA in the periphery corresponds to cognitive status in clade C as it does in clade B and recombinant forms. A cross-sectional study was conducted on participants investigated for HIV-associated neurocognitive impairment in South Africa. HIV-1 proviral DNA was quantified using a PCR assay targeting a highly conserved HIV-1 LTR-gag region. Fifty-four (36.7%) participants were cognitively impaired and 93 (63.3%) were not impaired. Forty-three (79.6%) of the cognitively impaired participants were female and 11 (20.4%) were male. There was no significant age difference between cognitively impaired and unimpaired participants (p = 0.42). HIV-1 DNA in cognitively impaired PLWH was significantly higher than in cognitively normal individuals (p = .016). Considering impaired participants, lymphocyte HIV-1 DNA was significantly higher in males than females (p = 0.02). There was a modest positive correlation between lymphocyte HIV-1 DNA and global deficit scores (GDS) r = 0.176; p = 0.03). The two measures of viral load, lymphocyte HIV-1 DNA copies/million and plasma RNA copies/ml, were positively correlated (r = 0.39; p < .001). After adjusting for other covariates, age, sex, treatment status, and the interactions between impairment and treatment, the multivariate regression showed association between proviral load and neurocognitive impairment; omega effect size was 0.04, p value = 0.010. The burden of HIV-1 peripheral blood lymphocyte proviral DNA corresponds to neurocognitive impairment among individuals infected with clade C disease. Therefore, therapeutic strategies to reduce the HIV-1 proviral DNA reservoir in lymphocytes may improve neurocognitive outcomes in PLWH.