7T Brain MRS in HIV Infection: Correlation with Cognitive Impairment and Performance on Neuropsychological Tests

CD14+CD16+ monocyte transmigration across the blood-brain barrier is associated with HIV-NCI despite viral suppression

HIV-associated neurocognitive impairment (HIV-NCI) affects 15%-50% of people with HIV (PWH), despite viral suppression with antiretroviral therapy (ART). HIV neuropathogenesis is mediated, in part, by transmigration of infected CD14+CD16+ monocytes across the blood-brain barrier (BBB) into the central nervous system (CNS). In the CNS, CD14+CD16+ monocytes contribute to infection and activation of parenchymal cells, resulting in production of neurotoxic viral and host factors that cause neuronal damage. Mechanisms by which CD14+CD16+ monocytes contribute to HIV-NCI have not been characterized in a study population of PWH on ART without contribution from confounders that affect cognition (e.g., substance use, hepatitis C virus coinfection). We assessed cognitive function, PBMC transmigration across the BBB, and neuronal health markers in a well-defined cohort of 56 PWH on ART using stringent criteria to eliminate confounding factors. We demonstrated that PWH on ART with HIV-NCI have significantly increased transmigration of their CD14+CD16+ monocytes across the BBB compared with those with normal cognition. We showed that hypertension and diabetes may be effect modifiers on the association between CD14+CD16+ monocyte transmigration and cognition. This study underscored the persistent role of CD14+CD16+ monocytes in HIV-NCI, even in PWH with viral suppression, suggesting them as potential targets for therapeutic interventions.

Brain N -acetyl-aspartyl-glutamate is associated with cognitive function in older virally suppressed people with HIV

OBJECTIVES

Cognitive impairment persists in virally suppressed people with HIV (VS-PWH) especially in higher order domains. One cortical circuit, linked to these domains, is regulated by N -acetyl-aspartyl glutamate (NAAG), the endogenous agonist of the metabotropic glutamate receptor 3. The enzyme glutamate carboxypeptidase II (GCPII) catabolizes NAAG and is upregulated in aging and disease. Inhibition of GCPII increases brain NAAG and improves learning and memory in rodent and primate models.

DESIGN

As higher order cognitive impairment is present in VS-PWH, and NAAG has not been investigated in earlier magnetic resonance spectroscopy studies (MRS), we investigated if brain NAAG levels measured by MRS were associated with cognitive function.

METHODS

We conducted a retrospective analysis of 7-Tesla MRS data from a previously published study on cognition in older VS-PWH. The original study did not separately quantify NAAG, therefore, work for this report focused on relationships between regional NAAG levels in frontal white matter (FWM), left hippocampus, left basal ganglia and domain-specific cognitive performance in 40 VS-PWH after adjusting for confounds. Participants were older than 50 years, negative for affective and neurologic disorders, and had no prior 3-month psychoactive-substance use.

RESULTS

Higher NAAG levels in FWM were associated with better attention/working memory. Higher left basal ganglia NAAG related to better verbal fluency. There was a positive relationship between hippocampal NAAG and executive function which lost significance after correction for confounds.

CONCLUSION

These data suggest brain NAAG serves as a biomarker of cognition in VS-PWH. Pharmacological modulation of brain NAAG warrants investigation as a therapeutic approach for cognitive deficits in VS-PWH.

Multimodal Approach to Neurocognitive Function in People Living with HIV in the cART Era: A Comprehensive Review

Combination antiretroviral treatment (cART) has revolutionized the management of human immunodeficiency virus (HIV) and has markedly improved the disease burden and life expectancy of people living with HIV. HIV enters the central nervous system (CNS) early in the course of infection, establishes latency, and produces a pro-inflammatory milieu that may affect cognitive functions, even in the cART era. Whereas severe forms of neurocognitive impairment (NCI) such as HIV-associated dementia have declined over the last decades, milder forms have become more prevalent, are commonly multifactorial, and are associated with comorbidity burdens, mental health, cART neurotoxicity, and ageing. Since 2007, the Frascati criteria have been used to characterize and classify HIV-associated neurocognitive disorders (HAND) into three stages, namely asymptomatic neurocognitive impairment (ANI), mild neurocognitive disorder (MND), and HIV-associated dementia (HAD). These criteria are based on a comprehensive neuropsychological assessment that presupposes the availability of validated, demographically adjusted, and normative population data. Novel neuroimaging modalities and biomarkers have been proposed in order to complement NCI assessments, elucidate neuropathogenic mechanisms, and support HIV-associated NCI diagnosis, monitoring, and prognosis. By integrating neuropsychological assessments with biomarkers and neuroimaging into a holistic care approach, clinicians can enhance diagnostic accuracy, prognosis, and patient outcomes. This review interrogates the value of these modes of assessment and proposes a unified approach to NCI diagnosis.

Altered metabolism in right basal ganglia associated with asymptomatic neurocognitive impairment in HIV-infected individuals

Background

Only few studies have focused on the metabolite differences between asymptomatic neurocognitive impairment (ANI) and cognitively normal people living with HIV (PLWH). The current study aims to examine whether brain metabolisms in basal ganglia (BG) by magnetic resonance spectroscopy (MRS) were potential to discriminate ANI from cognitively normal PLWH.

Methods

According to neuropsychological (NP) test, 80 PLWH (37.4 ± 10.2 years) were divided into ANI group (HIV-ANI, n = 31) and NP normal group (HIV-normal, n = 49). Brain metabolisms by MRS from right BG were compared between groups, including N-acetylaspartate and N-acetyl aspartylglutamate (tNAA), creatine and phosphocreatine (tCr), and choline-containing compounds (tCho). A total value of three metabolites were introduced. All brain metabolisms were evaluated as its percentage of total. Furthermore, correlations between MRS and NP and clinical measures were evaluated. A logistic regression model was applied, and the AUC values for the model and the continuous factors were compared using receiver operating curve (ROC) analysis.

Results

Compared to HIV-normal group, tNAA/total was lower and tCr/total was higher in the HIV-ANI group (P < 0.05). Both tNAA/total and tCr/total values were correlated with NP score (P < 0.05), especially in verbal fluency, speed of information processing, learning, and recall (P < 0.05). The logistic model included BG-tCr/total, current CD4 and infection years of PLWH. The AUC value for the BG-tCr/total was 0.696 and was not significantly lower than that for logistic model (P < 0.01).

Conclusion

The altered brain metabolites in the right BG were found in the ANI group compared to PLWH with normal cognition, and further associated with NP deficits. The current findings indicated that brain metabolites assessed by MRS has the potential to discriminate ANI from cognitively normal PLWH.

Frequency-dependent functional alterations in people living with HIV with early stage of HIV-associated neurocognitive disorder

Background

HIV enters the brain soon after seroconversion and causes HIV-associated neurocognitive disorder (HAND). However, the pathogenesis of this insidious impairment at an early stage remains unclear.

Objectives

To explore functional integration and segregation changes at the early stages of HAND, voxel-level indices of regional homogeneity (ReHo), the amplitude of low-frequency fluctuations (ALFF), and voxel-mirrored homotopic connectivity (VMHC) under two different frequency bands (slow-5: 0.01-0.027 Hz; slow-4: 0.027-0.073 Hz) were analyzed.

Methods

Ninety-eight people living with HIV (PLWH) and 44 seronegative controls underwent resting-state functional magnetic resonance imaging. Furthermore, all PLWHs underwent neuropsychological and daily functioning tests. The main effect of the group and the interaction between the group and frequency band were investigated. Finally, the relationship between the altered indices and the cognitive domains was explored.

Results

A significant group-by-frequency interaction was demonstrated in the right thalamus for ReHo; for VMHC, the interaction was observed in the bilateral precuneus and paracentral gyrus. The post hoc Bonferroni test indicated that the alteration of ReHo and VMHC could only be detected in slow-5. PLWH showed significantly reduced ALFF in both the frequency bands in the right occipital gyrus and right calcarine. Moreover, some altered functional integration and segregation indices are related to impaired cognitive function.

Conclusion

People living with HIV displayed aberrant functional integration and segregation at the early stages of HAND, which is linked to cognitive function. The frequency band of slow-5 might be more sensitive for detecting insidious damage at an early stage.

Co-Infection and Cancer: Host–Pathogen Interaction between Dendritic Cells and HIV-1, HTLV-1, and Other Oncogenic Viruses

Dendritic cells (DCs) function as a link between innate and adaptive immune responses. Retroviruses HIV-1 and HTLV-1 modulate DCs to their advantage and utilize them to propagate infection. Coinfection of HTLV-1 and HIV-1 has implications for cancer malignancies. Both viruses initially infect DCs and propagate the infection to CD4+ T cells through cell-to-cell transmission using mechanisms including the formation of virologic synapses, viral biofilms, and conduits. These retroviruses are both neurotrophic with neurovirulence determinants. The neuropathogenesis of HIV-1 and HTLV-1 results in neurodegenerative diseases such as HIV-associated neurocognitive disorders (HAND) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Infected DCs are known to traffic to the brain (CNS) and periphery (PNS, lymphatics) to induce neurodegeneration in HAND and HAM/TSP patients. Elevated levels of neuroinflammation have been correlated with cognitive decline and impairment of motor control performance. Current vaccinations and therapeutics for HIV-1 and HTLV-1 are assessed and can be applied to patients with HIV-1-associated cancers and adult T cell leukemia/lymphoma (ATL). These diseases caused by co-infections can result in both neurodegeneration and cancer. There are associations with cancer malignancies and HIV-1 and HTLV-1 as well as other human oncogenic viruses (EBV, HBV, HCV, HDV, and HPV). This review contains current knowledge on DC sensing of HIV-1 and HTLV-1 including DC-SIGN, Tat, Tax, and current viral therapies. An overview of DC interaction with oncogenic viruses including EBV, Hepatitis viruses, and HPV is also provided. Vaccines and therapeutics targeting host–pathogen interactions can provide a solution to co-infections, neurodegeneration, and cancer.

Cingulate transcranial direct current stimulation in adults with HIV

BACKGROUND

Neuronal dysfunction plays an important role in the high prevalence of HIV-associated neurocognitive disorders (HAND) in people with HIV (PWH). Transcranial direct current stimulation (tDCS)-with its capability to improve neuronal function-may have the potential to serve as an alternative therapeutic approach for HAND. Brain imaging and neurobehavioral studies provide converging evidence that injury to the anterior cingulate cortex (ACC) is highly prevalent and contributes to HAND in PWH, suggesting that ACC may serve as a potential neuromodulation target for HAND. Here we conducted a randomized, double-blind, placebo-controlled, partial crossover pilot study to test the safety, tolerability, and potential efficacy of anodal tDCS over cingulate cortex in adults with HIV, with a focus on the dorsal ACC (dACC).

METHODS

Eleven PWH (47-69 years old, 2 females, 100% African Americans, disease duration 16-36 years) participated in the study, which had two phases, Phase 1 and Phase 2. During Phase 1, participants were randomized to receive ten sessions of sham (n = 4) or cingulate tDCS (n = 7) over the course of 2-3 weeks. Treatment assignments were unknown to the participants and the technicians. Neuropsychology and MRI data were collected from four additional study visits to assess treatment effects, including one baseline visit (BL, prior to treatment) and three follow-up visits (FU1, FU2, and FU3, approximately 1 week, 3 weeks, and 3 months after treatment, respectively). Treatment assignment was unblinded after FU3. Participants in the sham group repeated the study with open-label cingulate tDCS during Phase 2. Statistical analysis was limited to data from Phase 1.

RESULTS

Compared to sham tDCS, cingulate tDCS led to a decrease in Perseverative Errors in Wisconsin Card Sorting Test (WCST), but not Non-Perseverative Errors, as well as a decrease in the ratio score of Trail Making Test-Part B (TMT-B) to TMT-Part A (TMT-A). Seed-to-voxel analysis with resting state functional MRI data revealed an increase in functional connectivity between the bilateral dACC and a cluster in the right dorsal striatum after cingulate tDCS. There were no differences in self-reported discomfort ratings between sham and cingulate tDCS.

CONCLUSIONS

Cingulate tDCS is safe and well-tolerated in PWH, and may have the potential to improve cognitive performance and brain function. A future study with a larger sample is warranted.

COVID-19-related cognitive dysfunction may be associated with transient disruption in the DLPFC glutamatergic pathway

Cognitive impairment has recently attracted researchers as one of the possible neuropsychiatric manifestations of COVID-19, although how the infection perpetuates impairment of cognitive functions is still obscure. We presented a 29-year-old male patient with COVID-19 who developed new-onset transient attention deficit and memory problems following a SARS-CoV-2 infection. Structural neuroimaging was normal. MR-spectroscopy (MRS) of the bilateral DLPFC revealed significant for decreased levels of N-acetylaspartate (NAA), glutamate, and glutamate/glutamine ratio. After a follow-up without any medical treatment but with suggestions of memory exercises for three months a control MRS screening of DLPFC showed improved levels of NAA, glutamate, and glutamate/glutamine ratio. This report may suggest that cognitive deficits in SARS-CoV-2 infection can result from glutamatergic dysfunction with decreased NAA and glutamate levels in bilateral DLPFC.

Independent and Combined Effects of Nicotine or Chronic Tobacco Smoking and HIV on the Brain: A Review of Preclinical and Clinical Studies

Tobacco smoking is highly prevalent among HIV-infected individuals. Chronic smokers with HIV showed greater cognitive deficits and impulsivity, and had more psychopathological symptoms and greater neuroinflammation than HIV non-smokers or smokers without HIV infection. However, preclinical studies that evaluated the combined effects of HIV-infection and tobacco smoking are scare. The preclinical models typically used cell cultures or animal models that involved specific HIV viral proteins or the administration of nicotine to rodents. These preclinical models consistently demonstrated that nicotine had neuroprotective and anti-inflammatory effects, leading to cognitive enhancement. Although the major addictive ingredient in tobacco smoking is nicotine, chronic smoking does not lead to improved cognitive function in humans. Therefore, preclinical studies designed to unravel the interactive effects of chronic tobacco smoking and HIV infection are needed. In this review, we summarized the preclinical studies that demonstrated the neuroprotective effects of nicotine, the neurotoxic effects of the HIV viral proteins, and the scant literature on nicotine or tobacco smoke in HIV transgenic rat models. We also reviewed the clinical studies that evaluated the neurotoxic effects of tobacco smoking, HIV infection and their combined effects on the brain, including studies that evaluated the cognitive and behavioral assessments, as well as neuroimaging measures. Lastly, we compared the different approaches between preclinical and clinical studies, identified some gaps and proposed some future directions. Graphical abstract Independent and combined effects of HIV and tobacco/nicotine. Left top and bottom panels: Both clinical studies of HIV infected persons and preclinical studies using viral proteins in vitro or in vivo in animal models showed that HIV infection could lead to neurotoxicity and neuroinflammation. Right top and bottom panels: While clinical studies of tobacco smoking consistently showed deleterious effects of smoking, clinical and preclinical studies that used nicotine show mild cognitive enhancement, neuroprotective and possibly anti-inflammatory effects. In the developing brain, however, nicotine is neurotoxic. Middle overlapping panels: Clinical studies of persons with HIV who were smokers typically showed additive deleterious effects of HIV and tobacco smoking. However, in the preclinical studies, when nicotine was administered to the HIV-1 Tg rats, the neurotoxic effects of HIV were attenuated, but tobacco smoke worsened the inflammatory cascade.

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.

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.

The Glutamate System as a Crucial Regulator of CNS Toxicity and Survival of HIV Reservoirs

Glutamate (Glu) is the most abundant excitatory neurotransmitter in the central nervous system (CNS). HIV-1 and viral proteins compromise glutamate synaptic transmission, resulting in poor cell-to-cell signaling and bystander toxicity. In this study, we identified that myeloid HIV-1-brain reservoirs survive in Glu and glutamine (Gln) as a major source of energy. Thus, we found a link between synaptic compromise, metabolomics of viral reservoirs, and viral persistence. In the current manuscript we will discuss all these interactions and the potential to achieve eradication and cure using this unique metabolic profile.

Use of Neuroimaging to Inform Optimal Neurocognitive Criteria for Detecting HIV-Associated Brain Abnormalities

OBJECTIVE

Frascati international research criteria for HIV-associated neurocognitive disorders (HAND) are controversial; some investigators have argued that Frascati criteria are too liberal, resulting in a high false positive rate. Meyer et al. recommended more conservative revisions to HAND criteria, including exploring other commonly used methodologies for neurocognitive impairment (NCI) in HIV including the global deficit score (GDS). This study compares NCI classifications by Frascati, Meyer, and GDS methods, in relation to neuroimaging markers of brain integrity in HIV.

METHOD

Two hundred forty-one people living with HIV (PLWH) without current substance use disorder or severe (confounding) comorbid conditions underwent comprehensive neurocognitive testing and brain structural magnetic resonance imaging and magnetic resonance spectroscopy. Participants were classified using Frascati criteria versus Meyer criteria: concordant unimpaired [Frascati(Un)/Meyer(Un)], concordant impaired [Frascati(Imp)/Meyer(Imp)], or discordant [Frascati(Imp)/Meyer(Un)] which were impaired via Frascati criteria but unimpaired via Meyer criteria. To investigate the GDS versus Meyer criteria, the same groupings were utilized using GDS criteria instead of Frascati criteria.

RESULTS

When examining Frascati versus Meyer criteria, discordant Frascati(Imp)/Meyer(Un) individuals had less cortical gray matter, greater sulcal cerebrospinal fluid volume, and greater evidence of neuroinflammation (i.e., choline) than concordant Frascati(Un)/Meyer(Un) individuals. GDS versus Meyer comparisons indicated that discordant GDS(Imp)/Meyer(Un) individuals had less cortical gray matter and lower levels of energy metabolism (i.e., creatine) than concordant GDS(Un)/Meyer(Un) individuals. In both sets of analyses, the discordant group did not differ from the concordant impaired group on any neuroimaging measure.

CONCLUSIONS

The Meyer criteria failed to capture a substantial portion of PLWH with brain abnormalities. These findings support continued use of Frascati or GDS criteria to detect HIV-associated CNS dysfunction.

Distinguishing Brain Impact of Aging and HIV Severity in Chronic HIV Using Multiparametric MR Imaging and MR Spectroscopy

Background

Combination antiretroviral therapy (cART) has transformed HIV into a manageable but complex chronic disease, in which it is uncertain which brain insults may relate to age vs initial disease severity. We evaluate N-acetyl-aspartate/creatine (NAA/Cr), white matter hyperintensities (WMH), and mean cortical thickness to identify which subclinical markers of brain insult best relate to CD4 nadir and aging. This is a prospective study of the association between brain markers with age and initial infection severity, based on CD4 nadir, in chronic HIV patients.

Methods

Thirty-seven chronic HIV patients (age 25–77 years) with successful viral suppression were scanned on a GE 3T magnetic resonance imaging scanner to obtain NAA/Cr (standardized and averaged over 5 brain regions), log-transformed WMH volume, and mean cortical thickness. The brain measures were fitted with both CD4 nadir and age to evaluate the significance of their relationship.

Results

NAA/Cr, WMH, and cortical thickness were all correlated with age and CD4 nadir in unadjusted associations. Stepwise regression models showed that NAA/Cr alone best predicted CD4 nadir (β = 40.1 ± 13.3; P = .005), whereas WMH (β = 2.3 ± .9; P = .02) and mean cortical thickness (β = –2.7 ± 6.6; P < .0001) together produced the best model fit with age. NAA/Cr was higher for HIV stage 1 (CD4 nadir ≥ 500 cells/ µL; n = 15) compared with stage 2 (200 ≥ CD4 nadir < 500; n = 13) and stage 3 (CD4 nadir < 200; n = 9; P < .01 for both).

Conclusions

In patients with effectively suppressed HIV, NAA reflects the subclinical brain impact of initial disease severity related to development of even mild immune compromise, whereas cortical thickness and WMH volume are useful to evaluate age-related changes.