Biomarker evidence of axonal injury in neuroasymptomatic HIV-1 patients

Autoantibody-mediated disorders of the central and peripheral nervous system: Overview Infection

HIV-associated neurocognitive disorders are a common manifestation of HIV infection, affecting more than half of HIV-infected individuals, including those receiving targeted antiviral therapy. A common feature of the course of HIV infection during therapy is large-scale immune responses in the brain. Several pathways are involved in the neuropathogenesis of HIV infection: Cellular entry, inflammatory processes in microglia, activation of astroglia, myeloid cells, and damage to brain vessels leading to neurocirculatory disorders. Data on vascular diseases that influence the development of neurocognitive impairment in HIV-positive patients will also be examined, as well as better intervention strategies for complex neurocognitive disorders and neurodegenerative processes in HIV infection.

Cerebrospinal fluid biomarkers of inflammation and immune activation associated with neurocognitive impairment among US Latinos with HIV

OBJECTIVE

Examine the association between markers of inflammation in the cerebrospinal fluid (CSF) and neurocognitive impairment (NCI) among diverse persons with HIV (PWH).

BACKGROUND

Latino PWH are at higher risk for NCI than non-Latino White PWH (NLW). Evidence of inflammation in CSF can be higher among racial and ethnic minority PWH and has been linked to NCI.

METHODS

We performed a retrospective cross-sectional analysis of 363 PWH who identified as Latinos or NLW. Neurocognitive performance was measured by a comprehensive battery. A focused panel of biomarkers [interleukin-6 (IL-6), soluble CD14 (sCD14), interferon-γ-inducible protein-10 (IP-10), neurofilament light chain (NFL)] was measured in CSF by immunoassay. Covariates included demographic, HIV disease, medical, psychiatric, and substance use characteristics.

RESULTS

The cohort consisted of 126 Latinos and 237 NLW (age: M  = 42.5, SD  = 11.0, 88% male, 51.5% AIDS history; 64% on antiretroviral therapy). Latinos had significantly higher NFL levels than NLW ( P  < 0.0001, adjusted Cohen's d 1.15), but not among virally-suppressed PWH. In the entire cohort, higher sCD14 was associated with NCI (adjusted odds ratio (aOR) = 2.6, confidence interval (CI) = 1.1-6.5] after adjusting for statistically significant covariates.

CONCLUSIONS

We did not identify a relationship between ethnicity, inflammation and NCI in this cohort. Future studies might examine sociocultural factors leading to increased inflammation in the CSF in diverse PWH.

Neuropathogenesis of acute HIV: mechanisms, biomarkers, and therapeutic approaches

PURPOSE OF REVIEW

The neuropathogenesis of acute HIV leads to rapid central nervous system (CNS) involvement, characterized by early viral entry, immune activation, and the formation of viral reservoirs. Despite effective antiretroviral therapy (ART), these reservoirs persist, drive neuroinflammation and injury and lead to HIV-associated neurodegenerative disorders (HAND). This review provides an updated synthesis of the mechanisms in acute HIV neuropathogenesis, biomarkers of CNS injury and emerging therapeutic approaches. A deeper understanding of these mechanisms is critical for addressing persistent HAND in ART-treated individuals.

RECENT FINDINGS

Growing evidence now supports the principal role of infected CD4 + T cells in mediating HIV neuroinvasion alongside monocytes, resulting in seeding in perivascular macrophages, pericytes, and adjacent microglia and astrocytes. These reservoirs contribute to ongoing transcriptional activity and viral persistence despite antiretroviral therapy. Neuroinflammation, driven by activated microglia, astrocytes, inflammasomes, and neurotoxic viral proteins, disrupts neuronal homeostasis. Emerging therapies, including latency-reversing agents and transcription inhibitors, show promise in reducing neuroinflammation and reservoir activity.

SUMMARY

Understanding the mechanisms of HIV neuropathogenesis and reservoir persistence has significant implications for developing targeted therapies to mitigate HAND. Strategies to eliminate CNS reservoirs and reduce neuroinflammation should be prioritized to improve long-term cognitive outcomes in people with HIV.

Asymptomatic Cerebrospinal Fluid HIV-1 Escape: Incidence and Consequences

BACKGROUND

The incidence and clinical relevance of asymptomatic cerebrospinal fluid escape (CSFE) during antiretroviral therapy (ART) is uncertain. We examined the impact and incidence of asymptomatic CSFE in a Swedish HIV cohort.

METHODS

Neuroasymptomatic people with HIV (PWH) who have been on ART for at least 6 months with suppressed plasma viral load were followed longitudinally. CSFE was defined as either increased CSF HIV-1 RNA with concurrent plasma suppression or CSF HIV-1 RNA exceeding that in plasma when both were quantifiable. Paired CSF and plasma were analyzed for HIV-1 RNA, neopterin, neurofilament light protein (NfL), white blood cell (WBC) count, and albumin ratio.

RESULTS

Asymptomatic CSFE (cutoff 50 copies/mL) was found in 4 of 173 PWH (2%) and 5 of 449 samples (1%). The corresponding proportions were 8% of PWH and 4% for samples using a 20 copies/mL cutoff for CSF HIV-1 RNA. CSFE samples (cutoff 20 copies/mL) had a 25% higher geometric mean of CSF neopterin (P = .01) and 8% higher albumin ratio (P = .04) compared to samples without CSFE. No differences were observed in CSF NfL levels (P = .8). The odds ratio for increased CSF WBC (≥ 3 cells/μL) in samples with CSFE was 3.9 (P = .004), compared to samples without elevated CSF viral load.

CONCLUSIONS

Asymptomatic CSFE was identified in only 4 (2%) PWH, with no cases of continuous CSFE observed. Increased CSF HIV-1 RNA was associated with biomarkers of CNS immune activation and blood-brain barrier impairment, but not with biomarkers of neuronal injury.

Body Fluid Biomarkers of Neurological Injury in HIV-1-Associated Neurocognitive Disorder

Since combined antiretroviral therapy for human immunodeficiency virus-associated neurocognitive dysfunction (HAND) only slows the disease's progression, early identification and timely intervention are crucial for effective therapy. In this article, we review the latest evidence in body fluid biomarkers of HAND, providing an overview of research conducted on cerebrospinal fluid and blood samples to draw conclusions on promising biomarkers. Although the significance of biomarkers such as amyloid metabolites, tau proteins, neurofilament light chain, myelin oligodendrocyte glycoprotein, and brain-derived neurotrophic factor in the early detection of HAND may not be immediately clear, they could potentially play a crucial role in evaluating prognosis and tracking the effectiveness of treatment.

Viruses and the Brain-A Relationship Prone to Trouble

Neurological disorders, some of which are associated with viral infections, are growing due to the aging and expanding population. Despite strong defenses of the central nervous system, some viruses have evolved ways to breach them, which often result in dire consequences. In this review, we recount the various ways by which different viruses can enter the CNS, and we describe the consequences of such invasions. Consequences may manifest as acute disease, such as encephalitis, meningitis, or result in long-term effects, such as neuromuscular dysfunction, as occurs in poliomyelitis. We discuss evidence for viral involvement in the causation of well-known chronic neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, multiple sclerosis, as well as vascular dementia in the elderly. We also describe the approaches currently available to control a few of the neural viral infections. These include antivirals that are effective against human immunodeficiency virus and herpes simplex virus, as well as vaccines valuable for controlling rabies virus, poliomyelitis virus, and some flavivirus infections. There is an urgent need to better understand, at a molecular level, how viruses contribute to acute and, especially, chronic neurological diseases and to develop more precise and effective vaccines and therapies.

Head-to-Head Comparison of Aptamer- and Antibody-Based Proteomic Platforms in Human Cerebrospinal Fluid Samples from a Real-World Memory Clinic Cohort

High-throughput proteomic platforms are crucial to identify novel Alzheimer's disease (AD) biomarkers and pathways. In this study, we evaluated the reproducibility and reliability of aptamer-based (SomaScan® 7k) and antibody-based (Olink® Explore 3k) proteomic platforms in cerebrospinal fluid (CSF) samples from the Ace Alzheimer Center Barcelona real-world cohort. Intra- and inter-platform reproducibility were evaluated through correlations between two independent SomaScan® assays analyzing the same samples, and between SomaScan® and Olink® results. Association analyses were performed between proteomic measures, CSF biological traits, sample demographics, and AD endophenotypes. Our 12-category metric of reproducibility combining correlation analyses identified 2428 highly reproducible SomaScan CSF measures, with over 600 proteins well reproduced on another proteomic platform. The association analyses among AD clinical phenotypes revealed that the significant associations mainly involved reproducible proteins. The validation of reproducibility in these novel proteomics platforms, measured using this scarce biomaterial, is essential for accurate analysis and proper interpretation of innovative results. This classification metric could enhance confidence in multiplexed proteomic platforms and improve the design of future panels.

The Impact of HIV on Early Brain Aging-A Pathophysiological (Re)View

Background/Objectives: This review aims to provide a comprehensive understanding of how HIV alters normal aging trajectories in the brain, presenting the HIV-related molecular mechanisms and pathophysiological pathways involved in brain aging. The review explores the roles of inflammation, oxidative stress, and viral persistence in the brain, highlighting how these factors contribute to neuronal damage and cognitive impairment and accelerate normal brain aging. Additionally, it also addresses the impact of antiretroviral therapy on brain aging and the biological markers associated with its occurrence. Methods: We extensively searched PubMed for English-language articles published from 2000 to 2024. The following keywords were used in the search: "HIV", "brain", "brain aging", "neuroinflammation", "HAART", and "HAND". This strategy yielded 250 articles for inclusion in our review. Results: A combination of blood-brain barrier dysfunction, with the direct effects of HIV on the central nervous system, chronic neuroinflammation, telomere shortening, neurogenesis impairments, and neurotoxicity associated with antiretroviral treatment (ART), alters and amplifies the mechanisms of normal brain aging. Conclusions: Current evidence suggests that HIV infection accelerates neurodegenerative processes of normal brain aging, leading to cognitive decline and structural brain changes at an earlier age than typically observed in the general population.

Serum and CSF biomarkers in asymptomatic patients during primary HIV infection: a randomized study

It is debated whether CNS involvement begins during acute human immunodeficiency virus (HIV) infection in persons without meningitis/encephalitis and whether specific antiretroviral drugs or combinations would be beneficial. Neurologically asymptomatic participants enrolled in a randomized and controlled study comparing three combination antiretroviral regimens (tenofovir alafenamide/emtricitabine plus dolutegravir; darunavir; or both) during primary HIV infection were enrolled. Serum and CSF were collected at baseline and at 12 and 48 (serum only) weeks after treatment initiation. Single molecule array was used to measure neurofilament light chain (NFL), total tau protein (Tau), brain-derived neurotrophic factor, glial fibrillary acidic protein (GFAP) and ubiquitin C-terminal hydrolase. We assessed the longitudinal change in biomarkers over time, in addition to the change in the prevalence of serum NFL concentrations above previously published age-adjusted cut-offs (7 pg/ml if 5-18 years, 10 pg/ml if 18-51 years, 15 pg/ml if 51-61 years, 20 pg/ml if 61-70 years and 35 pg/ml if >70 years). Serum was available from 47 participants at all time points, and CSF was available from 13 participants at baseline and 7 at Week 12. We observed a significant direct serum-to-CSF correlation for NFL (ρ = 0.692, P = 0.009), GFAP (ρ = 0.659, P = 0.014) and brain-derived neurotrophic factor (ρ = 0.587, P = 0.045). Serum (ρ = 0.560, P = 0.046) and CSF NFL (ρ = 0.582, P = 0.037) concentrations were directly associated with CSF HIV RNA levels. We observed a significant decrease over time in serum NFL (P = 0.006) and GFAP (P = 0.006) but not in the other biomarkers. No significant difference was observed among the treatment arms. At baseline, serum and CSF age-adjusted NFL levels were above age-adjusted cut-offs in 23 (48.9%) and four participants (30.8%), respectively; considering serum NFL, this proportion was lower at Weeks 12 (31.9%, P = 0.057) and 48 (27.7%, P = 0.13). A relevant proportion of neurologically asymptomatic participants had abnormal CSF and serum NFL levels during primary HIV infection. NFL and GFAP decreased in serum following combination antiretroviral therapy without significant differences among the treatment arms.

Microglia and macrophages alterations in the CNS during acute SIV infection: A single-cell analysis in rhesus macaques

Human Immunodeficiency Virus (HIV) is widely acknowledged for its profound impact on the immune system. Although HIV primarily affects peripheral CD4 T cells, its influence on the central nervous system (CNS) cannot be overlooked. Within the brain, microglia and CNS-associated macrophages (CAMs) serve as the primary targets for HIV and the simian immunodeficiency virus (SIV) in nonhuman primates. This infection can lead to neurological effects and establish a viral reservoir. Given the gaps in our understanding of how these cells respond in vivo to acute CNS infection, we conducted single-cell RNA sequencing (scRNA-seq) on myeloid cells from the brains of three rhesus macaques 12 days after SIV infection, along with three uninfected controls. Our analysis revealed six distinct microglial clusters including homeostatic microglia, preactivated microglia, and activated microglia expressing high levels of inflammatory and disease-related molecules. In response to acute SIV infection, the homeostatic and preactivated microglia population decreased, while the activated and disease-related microglia increased. All microglial clusters exhibited upregulation of MHC class I molecules and interferon-related genes, indicating their crucial roles in defending against SIV during the acute phase. All microglia clusters also upregulated genes linked to cellular senescence. Additionally, we identified two distinct CAM populations: CD14lowCD16hi and CD14hiCD16low CAMs. Interestingly, during acute SIV infection, the dominant CAM population changed to one with an inflammatory phenotype. Specific upregulated genes within one microglia and one macrophage cluster were associated with neurodegenerative pathways, suggesting potential links to neurocognitive disorders. This research sheds light on the intricate interactions between viral infection, innate immune responses, and the CNS, providing valuable insights for future investigations.

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.

Global research trends on the links between NfL and neurological disorders: A bibliometric analysis and review

Background

The global incidence of neurological diseases has been on the rise, creating an urgent need for a validated marker. Neurofilament Light Chain (NfL) holds promise as such a marker and has garnered significant attention in the field of neurological diseases over the past decades.

Methods

Corresponding articles from 2013 to 2023 were collected from the Web of Science database, and data were analyzed by CiteSpace and VOSviewer software.

Results

A total of 1350 articles were collected from 296 countries/regions, involving 7246 research organizations. Since 2013, among the top ten institutions and authors with the highest number of published papers, the most are from the US and the UK. The United States leads in the number of published papers, but England holds a more momentous position, because it has higher IF. Henrik Zetterberg is the most influential scholar in the field.

Conclusions

The output of papers mainly relies on researchers from developed countries, and scholars from the United States and England have contributed the largest number of papers. Until now, the importance of NfL in neurological diseases has attracted global attention. In addition, NfL contributes to the potential diagnosis of various neurological disorders and can be used to improve the accuracy of differential diagnosis and prognostic assessment as well as predict the response to treatments. More and more in-depth studies are highly needed in the future.

Relationships between plasma neurofilament light chain protein, cognition, and brain aging in people with HIV

OBJECTIVE

Neurofilament light chain protein (NfL) is a marker of neuronal injury and neurodegeneration. Typically assessed in cerebrospinal fluid, recent advances have allowed this biomarker to be more easily measured in plasma. This study assesses plasma NfL in people with HIV (PWH) compared with people without HIV (PWoH), and its relationship with cognitive impairment, cardiovascular risk, and a neuroimaging metric of brain aging [brain-age gap (BAG)].

DESIGN

One hundred and four PWH (HIV RNA <50 copies/ml) and 42 PWoH provided blood samples and completed a cardiovascular risk score calculator, neuroimaging, and cognitive testing.

METHOD

Plasma NfL was compared between PWoH and PWH and assessed for relationships with age, HIV clinical markers, cardiovascular disease risk, cognition, and BAG (difference between a brain-predicted age and chronological age).

RESULTS

Plasma NfL was not significantly different between PWoH and PWH. Higher NfL related to increasing age in both groups. Plasma NfL was not associated with typical HIV disease variables. Within PWH, NfL was higher with higher cardiovascular risk, cognitive impairment and a greater BAG.

CONCLUSION

Virally suppressed PWH who are cognitively normal likely do not have significant ongoing neurodegeneration, as evidenced by similar plasma NfL compared with PWoH. However, NfL may represent a biomarker of cognitive impairment and brain aging in PWH. Further research examining NfL with longitudinal cognitive decline is needed to understand this relationship more fully.

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.

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.

Microglia and macrophages alterations in the CNS during acute SIV infection: a single-cell analysis in rhesus macaques

Human Immunodeficiency Virus (HIV) is widely acknowledged for its profound impact on the immune system. Although HIV primarily affects peripheral CD4 T cells, its influence on the central nervous system (CNS) cannot be overlooked. Within the brain, microglia and CNS-associated macrophages (CAMs) serve as the primary targets for HIV, as well as for the simian immunodeficiency virus (SIV) in nonhuman primates. This infection can lead to neurological effects and the establishment of a viral reservoir. Given the gaps in our understanding of how these cells respond in vivo to acute CNS infection, we conducted single-cell RNA sequencing (scRNA-seq) on myeloid cells from the brains of three rhesus macaques 12-days after SIV infection, along with three uninfected controls. Our analysis revealed six distinct microglial clusters including homeostatic microglia, preactivated microglia, and activated microglia expressing high levels of inflammatory and disease-related molecules. In response to acute SIV infection, the population of homeostatic and preactivated microglia decreased, while the activated and disease-related microglia increased. All microglial clusters exhibited upregulation of MHC class I molecules and interferon-related genes, indicating their crucial roles in defending against SIV during the acute phase. All microglia clusters also upregulated genes linked to cellular senescence. Additionally, we identified two distinct CAM populations: CD14lowCD16hi and CD14hiCD16low CAMs. Interestingly, during acute SIV infection, the dominant CAM population changed to one with an inflammatory phenotype. Notably, specific upregulated genes within one microglia and one macrophage cluster were associated with neurodegenerative pathways, suggesting potential links to neurocognitive disorders. This research sheds light on the intricate interactions between viral infection, innate immune responses, and the CNS, providing valuable insights for future investigations.

Fluid biomarkers of the neurovascular unit in cerebrovascular disease and vascular cognitive disorders: A systematic review and meta-analysis

Background

The disruption of the neurovascular unit (NVU), which maintains the integrity of the blood brain barrier (BBB), has been identified as a critical mechanism in the development of cerebrovascular and neurodegenerative disorders. However, the understanding of the pathophysiological mechanisms linking NVU dysfunction to the disorders is incomplete, and reliable blood biomarkers to measure NVU dysfunction are yet to be established. This systematic review and meta-analysis aimed to identify biomarkers associated with BBB dysfunction in large vessel disease, small vessel disease (SVD) and vascular cognitive disorders (VCD).

Methods

A literature search was conducted in PubMed, EMBASE, Scopus and PsychINFO to identify blood biomarkers related to dysfunction of the NVU in disorders with vascular pathologies published until 20 November 2023. Studies that assayed one or more specific markers in human serum or plasma were included. Quality of studies was assessed using the Newcastle-Ottawa Quality Assessment Scale. Effects were pooled and methodological heterogeneity examined using the random effects model.

Results

A total of 112 studies were included in this review. Where study numbers allowed, biomarkers were analysed using random effect meta-analysis for VCD (1 biomarker; 5 studies) and cerebrovascular disorders, including stroke and SVD (9 biomarkers; 29 studies) while all remaining biomarkers (n = 17 biomarkers; 78 studies) were examined through qualitative analysis. Results of the meta-analysis revealed that cerebrospinal fluid/serum albumin quotient (Q-Alb) reliably differentiates VCD patients from healthy controls (MD = 2.77; 95 % CI = 1.97-3.57; p < 0.0001) while commonly measured biomarkers of endothelial dysfunction (VEGF, VCAM-1, ICAM-1, vWF and E-selectin) and neuronal injury (NfL) were significantly elevated in vascular pathologies. A qualitative assessment of non-meta-analysed biomarkers revealed NSE, NfL, vWF, ICAM-1, VCAM-1, lipocalin-2, MMP-2 and MMP-9 levels to be upregulated in VCD, although these findings were not consistently replicated.

Conclusions

This review identifies several promising biomarkers of NVU dysfunction which require further validation. A panel of biomarkers representing multiple pathophysiological pathways may offer greater discriminative power in distinguishing possible disease mechanisms of VCD.

Vascular injury markers associated with cognitive impairment in people with HIV on suppressive antiretroviral therapy

OBJECTIVE

Human immunodeficiency virus (HIV)-associated neurocognitive disorders (HAND) remain prevalent despite viral suppression on antiretroviral therapy (ART). Vascular disease contributes to HAND, but peripheral markers that distinguish vascular cognitive impairment (VCI) from HIV-related etiologies remain unclear.

DESIGN

Cross-sectional study of vascular injury, inflammation, and central nervous system (CNS) injury markers in relation to HAND.

METHODS

Vascular injury (VCAM-1, ICAM-1, CRP), inflammation (IFN-γ, IL-1β, IL-6, IL-8, IL-15, IP-10, MCP-1, VEGF-A), and CNS injury (NFL, total Tau, GFAP, YKL-40) markers were measured in plasma and CSF from 248 individuals (143 HIV+ on suppressive ART and 105 HIV- controls).

RESULTS

Median age was 53 years, median CD4 + cell count, and duration of HIV infection were 505 cells/μl and 16 years, respectively. Vascular injury, inflammation, and CNS injury markers were increased in HIV+ compared with HIV- individuals ( P < 0.05). HAND was associated with increased plasma VCAM-1, ICAM-1, and YKL-40 ( P  < 0.01) and vascular disease ( P  = 0.004). In contrast, inflammation markers had no significant association with HAND. Vascular injury markers were associated with lower neurocognitive T scores in age-adjusted models ( P  < 0.01). Furthermore, plasma VCAM-1 correlated with NFL ( r  = 0.29, P  = 0.003). Biomarker clustering separated HAND into three clusters: two clusters with high prevalence of vascular disease, elevated VCAM-1 and NFL, and distinctive inflammation profiles (CRP/ICAM-1/YKL-40 or IL-6/IL-8/IL-15/MCP-1), and one cluster with no distinctive biomarker elevations.

CONCLUSIONS

Vascular injury markers are more closely related to HAND and CNS injury in PWH on suppressive ART than inflammation markers and may help to distinguish relative contributions of VCI to HAND.

Vascular injury markers associated with cognitive impairment in people with HIV on suppressive antiretroviral therapy

Objective

Human immunodeficiency virus (HIV)-associated neurocognitive disorders (HAND) remain prevalent despite viral suppression on antiretroviral therapy (ART). Vascular disease contributes to HAND, but peripheral markers that distinguish vascular cognitive impairment (VCI) from HIV-related etiologies remain unclear.

Design

Cross-sectional study of vascular injury, inflammation, and central nervous system (CNS) injury markers in relation to HAND.

Methods

Vascular injury (VCAM-1, ICAM-1, CRP), inflammation (IFN-γ, IL-1β, IL-6, IL-8, IL-15, IP-10, MCP-1, VEGF-A), and CNS injury (NFL, total Tau, GFAP, YKL-40) markers were measured in plasma and CSF from 248 individuals (143 HIV+ on suppressive ART and 105 HIV- controls).

Results

Median age was 53 years, median CD4 count, and duration of HIV infection were 505 cells/μl and 16 years, respectively. Vascular injury, inflammation, and CNS injury markers were increased in HIV+ compared with HIV- individuals (p<0.05). HAND was associated with increased plasma VCAM-1, ICAM-1, and YKL-40 (p<0.01) and vascular disease (p=0.004). In contrast, inflammation markers had no significant association with HAND. Vascular injury markers were associated with lower neurocognitive T scores in age-adjusted models (p<0.01). Furthermore, plasma VCAM-1 correlated with NFL (r=0.29, p=0.003). Biomarker clustering separated HAND into three clusters: two clusters with high prevalence of vascular disease, elevated VCAM-1 and NFL, and distinctive inflammation profiles (CRP/ICAM-1/YKL-40 or IL-6/IL-8/IL-15/MCP-1), and one cluster with no distinctive biomarker elevations.

Conclusions

Vascular injury markers are more closely related to HAND and CNS injury in PWH on suppressive ART than inflammation markers and may help to distinguish relative contributions of VCI to HAND.

Pre-analytical long-term stability of neopterin and neurofilament light in stored cerebrospinal fluid samples

OBJECTIVES

The aim of this study was to evaluate the impact of long-term sample storage on the concentrations of neopterin and neurofilament light (Nfl) in cerebrospinal fluid (CSF) samples. These are useful markers of neuroinflammation and neuronal damage and have been applied as biomarkers for several neurological diseases. However, different pre-analytical variables have potential to influence results.

METHODS

Twenty-one CSF samples donated by patients with HTLV-1-associated myelopathy (HAM) and stored for up to 11 years at -80 °C were retested after three-years for neopterin (n=10) and Nfl (n=11) by ELISA.

RESULTS

There was a strong correlation between the paired results (r>0.98, p<0.0001). Neopterin concentrations (nmol/L) ranged from 12.4 to 64 initially and from 11.5 to 64.4 when retested, with means (SD) of 30 (18.4) 1st test and 33 (19.1) 2nd test. Nfl concentrations (pg/mL) ranged from 79.9 to 3,733 initially and from 86.3 to 3,332, when retested with means (SD) of 1,138 (1,272) 1st test and 1,009 (1,114) at re-test.

CONCLUSIONS

Storing CSF samples at -80 °C appears not to impact the quantification of neopterin and Nfl allowing confidence in the reporting of archived samples.

Neurocognitive Dysfunction With Neuronal Injury in People With HIV on Long-Duration Antiretroviral Therapy

BACKGROUND AND OBJECTIVES

Neurologic outcomes in people with HIV (PWH) on long-duration antiretroviral therapy (ART) are not fully understood, and the underlying pathophysiology is unclear. To address this, we established a cohort of such individuals and compared them with HIV-negative controls using a novel matching technique. Both groups underwent extensive cognitive testing, evaluation for psychiatric measures, and MRI and CSF analyses.

METHODS

Participants underwent comprehensive neuropsychological testing and completed standardized questionnaires measuring depressive symptoms, perceptions of own functioning, and activities of daily living as part of an observational study. Brain MRI and lumbar puncture were optional. Coarsened Exact Matching was used to reduce between-group differences in age and sex, and weighted linear/logistic regression models were used to assess the effect of HIV on outcomes.

RESULTS

Data were analyzed from 155 PWH on ART for at least 15 years and 100 HIV-negative controls. Compared with controls, PWH scored lower in the domains of attention/working memory (PWH least square mean [LSM] = 50.4 vs controls LSM = 53.1, p = 0.008) and motor function (44.6 vs 47.7, p = 0.009) and a test of information processing speed (symbol search 30.3 vs 32.2, p = 0.003). They were more likely to self-report a higher number of cognitive difficulties in everyday life (p = 0.011). PWH also reported more depressive symptoms, general anxiety, and use of psychiatric medications (all with p < 0.05). PWH had reduced proportions of subcortical gray matter on MRI (β = -0.001, p < 0.001), and CSF showed elevated levels of neurofilament light chain (664 vs 529 pg/mL, p = 0.01) and tumor necrosis factor α (0.229 vs 0.156 ng/mL, p = 0.0008).

DISCUSSION

PWH, despite effective ART for over a decade, displayed neurocognitive deficits and mood abnormalities. MRI and CSF analyses revealed reduced brain volume and signs of ongoing neuronal injury and neuroinflammation. As the already large proportion of virologically controlled PWH continues to grow, longitudinal studies should be conducted to elucidate the implications of cognitive, psychiatric, MRI, and CSF abnormalities in this group.

Alzheimer's Disease Pathology in Middle Aged and Older People with HIV: Comparisons with Non-HIV Controls on a Healthy Aging and Alzheimer's Disease Trajectory and Relationships with Cognitive Function

We determined the prevalence of Alzheimer's disease (AD) pathological hallmarks, amyloid-β and phosphorylated-Tau, in autopsied brains of 49 people with HIV (PWH) (ages: 50-68; mean age = 57.0) from the National NeuroAIDS Tissue Consortium and in a comparative cohort of 55 people without HIV (PWoH) from the UC San Diego Alzheimer's Disease Research Center (17 controls, 14 mild cognitive impairment, 24 AD; ages: 70-102, mean age = 88.7). We examined how AD pathology relates to domain-specific cognitive functions in PWH overall and in sex-stratified samples. Amyloid-β and phosphorylated-Tau positivity (presence of pathology of any type/density) was determined via immunohistochemistry in AD-sensitive brain regions. Among PWH, amyloid-β positivity ranged from 19% (hippocampus) to 41% (frontal neocortex), and phosphorylated-Tau positivity ranged from 47% (entorhinal cortex) to 73% (transentorhinal cortex). Generally, AD pathology was significantly less prevalent, and less severe when present, in PWH versus PWoH regardless of cognitive status. Among PWH, positivity for AD pathology related most consistently to memory-related domains. Positivity for p-Tau pathology related to memory-related domains in women with HIV only, although the sample size of women with HIV was small (n = 10). Results indicate that AD pathology is present in a sizable portion of middle aged and older PWH, although not to the extent in older PWoH. Studies with better age-matched PWoH are needed to examine the effect of HIV status on AD pathology.

Cohort profile: a longitudinal study of HIV infection in the central nervous system with focus on cerebrospinal fluid - the Gothenburg HIV CSF Study Cohort

PURPOSE

In order to enable long-term follow-up of the natural course of HIV infection in the central nervous system, a longitudinal cohort study with repeated cerebrospinal fluid (CSF) analyses at intervals over time was initiated in 1985. When antiretrovirals against HIV were introduced in the late 1980s, short-term and long-term effects of various antiretroviral treatment (ART) regimens were added to the study.

PARTICIPANTS

All adult people living with HIV (PLWH) who were diagnosed at or referred to the Department of Infectious Diseases, Sahlgrenska University Hospital, Gothenburg, Sweden were asked to participate in the Gothenburg HIV CSF Study Cohort. PLWH with neurological symptoms or other clinical symptoms of HIV, as well as those with no symptoms of HIV infection, were included. Most participants were asymptomatic, which distinguishes this cohort from most other international HIV CSF studies. In addition, HIV-negative controls were recruited. These included people on HIV pre-exposure prophylaxis who served as lifestyle-matched controls to HIV-infected men who have sex with men. Since lumbar puncture (LP) is an invasive procedure, some PLHW only consented to participate in one examination. Furthermore, at the beginning of the study, several participants were lost to follow-up having died from AIDS. Of 662 PLWH where an initial LP was done, 415 agreed to continue with follow-up. Among the 415, 56 only gave permission to be followed with LP for less than 1 year, mainly to analyse the short-term effect of ART. The remaining 359 PLWH were followed up with repeated LP for periods ranging from >1 to 30 years. This group was defined as the 'longitudinal cohort'. So far, on 7 April 2022, 2650 LP and samplings of paired CSF/blood had been performed, providing a unique biobank.

FINDINGS TO DATE

A general finding during the 37-year study period was that HIV infection in the central nervous system, as mirrored by CSF findings, appears early in the infectious course of the disease and progresses slowly in the vast majority of untreated PLWH. Combination ART has been highly effective in reducing CSF viral counts, inflammation and markers of neural damage. Minor CSF signs of long-term sequels or residual inflammatory activity and CSF escape (viral CSF blips) have been observed during follow-up. The future course of these changes and their clinical impact require further studies.

FUTURE PLANS

PLWH today have a life expectancy close to that of non-infected people. Therefore, our cohort provides a unique opportunity to study the long-term effects of HIV infection in the central nervous system and the impact of ART and is an ongoing study.

Longitudinal decline of plasma neurofilament light levels after antiretroviral initiation in people living with HIV

BACKGROUND

This retrospective follow-up study aims to investigate the dynamic longitudinal change of plasma neurofilament light (NfL) levels after antiretroviral therapy (ART) initiation in a cohort of people living with human immunodeficiency virus (HIV) (PWH).

METHODS

We tested a convenience sample of 116 patients from the NORTHIV study. Plasma NfL levels-measured using Single molecule array (Simoa) technology-as well as other laboratory parameters were collected at baseline, weeks 4, 48, 96, and 144. Linear mixed-effects models were estimated to evaluate longitudinal change over time. Baseline CD4⁺ T-cell levels, CDC classification, and HIV RNA levels were considered. Models were adjusted by age, sex, treatment regimen, and baseline serum creatinine levels.

RESULTS

Plasma NfL levels were higher at baseline and also declined faster during the follow-up for participants with CD4⁺ count <100 cells/µl compared with >100 cells/µl. No significant difference was found between the CD4⁺ strata 100-199 and 200-499/µl. Participants with CDC classification stages B and C had higher levels of plasma NfL at baseline, as well as faster decline compared with participants with stage A. No significant main effects or change over time was found in baseline HIV RNA levels, treatment regimen, or sex.

CONCLUSION

Plasma NfL is a sensitive biomarker to assess ongoing central nervous system injury in PWH. Plasma NfL concentrations decline relatively fast following ART initiation and then stabilize after 48 weeks. Plasma NfL concentrations are associated with CD4⁺ count and stage of HIV disease. No correlations were seen with different ART regimens.

Update on Central Nervous System Effects of HIV in Adolescents and Young Adults

PURPOSE OF REVIEW

: Behaviorally acquired (non-perinatal) HIV infection during adolescence and young adulthood occurs in the midst of key brain developmental processes such as frontal lobe neuronal pruning and myelination of white matter, but we know little about the effects of new infection and therapy on the developing brain.

RECENT FINDINGS

Adolescents and young adults account for a disproportionately high fraction of new HIV infections each year. Limited data exist regarding neurocognitive performance in this age group, but suggest impairment is at least as prevalent as in older adults, despite lower viremia, higher CD4 + T cell counts, and shorter durations of infection in adolescents/young adults. Neuroimaging and neuropathologic studies specific to this population are underway. The full impact of HIV on brain growth and development in youth with behaviorally acquired HIV has yet to be determined; it must be investigated further to develop future targeted treatment and mitigation strategies.

Cohort profile: InfCareHIV, a prospective registry-based cohort study of people with diagnosed HIV in Sweden

PURPOSE

The Swedish InfCareHIV cohort was established in 2003 to ensure equal and effective care of people living with HIV (PLHIV) and enable long-term follow-up. InfCareHIV functions equally as a decision support system as a quality registry, ensuring up-to-date data reported in real time.

PARTICIPANTS

InfCareHIV includes data on >99% of all people with diagnosed HIV in Sweden and up to now 13 029 have been included in the cohort. InfCareHIV includes data on HIV-related biomarkers and antiretroviral therapies (ART) and also on demographics, patient-reported outcome measures and patient-reported experience measures.

FINDINGS TO DATE

Sweden was in 2015 the first country to reach the UNAIDS (United Nations Programme on HIV/AIDS)/WHO's 90-90-90 goals. Late diagnosis of HIV infection was identified as a key problem in the Swedish HIV-epidemic, and low-level HIV viraemia while on ART associated with all-cause mortality. Increased HIV RNA load in the cerebrospinal fluid (CSF) despite suppression of the plasma viral load was found in 5% of PLHIV, a phenomenon referred to as 'CSF viral escape'. Dolutegravir-based treatment in PLHIV with pre-existing nucleoside reverse transcriptase inhibitor-mutations was non-inferior to protease inhibitor-based regimens. An increase of transmitted drug resistance was observed in the InfCareHIV cohort. Lower efficacy for protease inhibitors was not due to lower adherence to treatment. Incidence of type 2 diabetes and insulin resistance was high in the ageing HIV population. Despite ART, the risk of infection-related cancer as well as lung cancer was increased in PLHIV compared with HIV-negative. PLHIV were less likely successfully treated for cervical precancer and more likely to have human papillomavirus types not included in current HPV vaccines. Self-reported sexual satisfaction in PLHIV is improving and is higher in women than men.

FUTURE PLANS

InfCareHIV provides a unique base to study and further improve long-term treatment outcomes, comorbidity management and health-related quality of life in people with HIV in Sweden.

The multifaceted role of neurofilament light chain protein in non-primary neurological diseases

The advancing validation and exploitation of CSF and blood neurofilament light chain protein as a biomarker of neuroaxonal damage has deeply changed the current diagnostic and prognostic approach to neurological diseases. Further, recent studies have provided evidence of potential new applications of this biomarker also in non-primary neurological diseases. In the present review we summarize the state of the art, future perspectives, but also limitations, of neurofilament light chain protein as a CSF and blood biomarker in several medical fields, including intensive care medicine, surgery, internal medicine and psychiatry. In particular, neurofilament light chain protein is associated with the degree of neurological impairment and outcome in patients admitted to intensive care units or in the perioperative phase and it seems to be highly interconnected with cardiovascular risk factors. Beyond that, interesting diagnostic and prognostic insights have been provided by the investigation of neurofilament light chain protein in psychiatric disorders as well as in the current coronavirus disease-19 pandemic and in normal ageing. Altogether, current data outline a multifaceted applicability of CSF and blood neurofilament light chain protein ranging from the critical clinical setting to the development of precision medicine models suggesting a strict interplay between the nervous system pathophysiology and the health-illness continuum.

Blood Biomarkers of Neuronal/Axonal and Glial Injury in Human Immunodeficiency Virus-Associated Neurocognitive Disorders

INTRODUCTION

Approximately half of the people living with HIV (PLWH) experience HIV-associated neurocognitive disorders (HANDs). However, the neuropathogenesis of HAND is complex, and identifying reliable biomarkers has been challenging.

METHODS

This study included 132 participants aged 50 and older from greater San Diego County. The participants were divided into three groups: PLWH with HAND (n = 29), PLWH without HAND (n = 73), and seronegatives without cognitive impairment (n = 30). Peripheral blood was collected at the clinical assessment, and plasma levels of neurofilament light chain (NfL), phosphorylated Tau 181 (pTau181), and glial fibrillary acidic protein (GFAP) were measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Plasma levels of NfL (but not pTau181 and GFAP) were significantly associated with HAND at a medium effect size (p = 0.039, Cohen's d = 0.45 for HAND + vs. HAND-). Notably, higher levels of NfL were significantly associated with HAND diagnosis even after adjusting for sex.

DISCUSSION

Our data suggest that neuronal degeneration (as evidenced by increased levels of NfL), but not tau pathology or glial degeneration, is related to cognitive status in PLWH. Our results corroborate the view that blood NfL is a promising biomarker of cognitive impairment in PLWH.

Rebound HIV-1 in cerebrospinal fluid after antiviral therapy interruption is mainly clonally amplified R5 T cell-tropic virus

HIV-1 persists as a latent reservoir in people receiving suppressive antiretroviral therapy (ART). When ART is interrupted (treatment interruption/TI), rebound virus re-initiates systemic infection in the lymphoid system. During TI, HIV-1 is also detected in cerebrospinal fluid (CSF), although the source of this rebound virus is unknown. To investigate whether there is a distinct HIV-1 reservoir in the central nervous system (CNS), we compared rebound virus after TI in the blood and CSF of 11 participants. Peak rebound CSF viral loads vary and we show that high viral loads and the appearance of clonally amplified viral lineages in the CSF are correlated with the transient influx of white blood cells. We found no evidence of rebound macrophage-tropic virus in the CSF, even in one individual who had macrophage-tropic HIV-1 in the CSF pre-therapy. We propose a model in which R5 T cell-tropic virus is released from infected T cells that enter the CNS from the blood (or are resident in the CNS during therapy), with clonal amplification of infected T cells and virus replication occurring in the CNS during TI.

Neuroimaging and immunological features of neurocognitive function related to substance use in people with HIV

This study sought to identify neuroimaging and immunological factors associated with substance use and that contribute to neurocognitive impairment (NCI) in people with HIV (PWH). We performed cross-sectional immunological phenotyping, neuroimaging, and neurocognitive testing on virally suppressed PWH in four substance groups: cocaine only users (COC), marijuana only users (MJ), dual users (Dual), and Non-users. Participants completed substance use assessments, multimodal MRI brain scan, neuropsychological testing, and blood and CSF sampling. We employed a two-stage analysis of 305 possible biomarkers of cognitive function associated with substance use. Feature reduction (Kruskal Wallis p-value < 0.05) identified 53 biomarkers associated with substance use (22 MRI and 31 immunological) for model inclusion along with clinical and demographic variables. We employed eXtreme Gradient Boosting (XGBoost) with these markers to predict cognitive function (global T-score). SHapley Additive exPlanations (SHAP) values were calculated to rank features for impact on model output and NCI. Participants were 110 PWH with sustained HIV viral suppression (33 MJ, 12 COC, 22 Dual, and 43 Non-users). The ten highest ranking biomarkers for predicting global T-score were 4 neuroimaging biomarkers including functional connectivity, gray matter volume, and white matter integrity; 5 soluble biomarkers (plasma glycine, alanine, lyso-phosphatidylcholine (lysoPC) aC17.0, hydroxy-sphingomyelin (SM.OH) C14.1, and phosphatidylcholinediacyl (PC aa) C28.1); and 1 clinical variable (nadir CD4 count). The results of our machine learning model suggest that substance use may indirectly contribute to NCI in PWH through both metabolomic and neuropathological mechanisms.

Brain neuronal and glial damage during acute COVID-19 infection in absence of clinical neurological manifestations

BACKGROUND

To assess whether SARS-CoV-2 infection may affect the central nervous system, specifically neurons and glia cells, even without clinical neurological involvement.

METHODS

In this single centre prospective study, serum levels of neurofilament light chain (sNfL) and glial fibrillar acidic protein (sGFAp) were assessed using SimoaTM assay Neurology 2-Plex B Assay Kit, in 148 hospitalised patients with COVID-19 without clinical neurological manifestations and compared them to 53 patients with interstitial pulmonary fibrosis (IPF) and 108 healthy controls (HCs).

RESULTS

Age and sex-corrected sNfL levels were higher in patients with COVID-19 (median log10-sNfL 1.41; IQR 1.04-1.83) than patients with IPF (median log10-sNfL 1.18; IQR 0.98-1.38; p<0.001) and HCs (median log10-sNfL 0.89; IQR 0.72-1.14; p<0.001). Likewise, age and sex-corrected sGFAP levels were higher in patients with COVID-19 (median log10-sGFAP 2.26; IQR 2.02-2.53) in comparison with patients with IPF (median log10-sGFAP 2.15; IQR 1.94-2.30; p<0.001) and HCs (median log10-sGFAP 1.87; IQR 0.64-2.09; p<0.001). No significant difference was found between patients with HCs and IPF (p=0.388 for sNfL and p=0.251 for sGFAp). In patients with COVID-19, a prognostic model with mortality as dependent variable (26/148 patients died during hospitalisation) and sNfl, sGFAp and age as independent variables, showed an area under curve of 0.72 (95% CI 0.59 to 0.84; negative predictive value (NPV) (%):80,positive predictive value (PPV)(%): 84; p=0.0008).

CONCLUSION

The results of our study suggest that neuronal and glial degeneration can occur in patients with COVID-19 regardless of overt clinical neurological manifestations. With age, levels of sNfl and GFAp can predict in-hospital COVID-19-associated mortality and might be useful to assess COVID-19 patient prognostic profile.

The effect of vitamin B supplementation on neuronal injury in people living with HIV: a randomized controlled trial

Effective antiretroviral therapy has radically changed the course of the HIV pandemic. However, despite efficient therapy, milder forms of neurocognitive symptoms are still present in people living with HIV. Plasma homocysteine is a marker of vitamin B deficiency and has been associated with cognitive impairment. People living with HIV have higher homocysteine concentrations than HIV-negative controls, and we have previously found an association between plasma homocysteine concentration and CSF concentration of neurofilament light protein, a sensitive marker for ongoing neuronal injury in HIV. This prompted us to perform this randomized controlled trial, to evaluate the effect of vitamin B supplementation on neuronal injury in a cohort of people living with HIV on stable antiretroviral therapy. At the Department of Infectious Diseases at Sahlgrenska University Hospital in Gothenburg, Sweden, 124 virally suppressed people living with HIV were screened to determine eligibility for this study. Sixty-one fulfilled the inclusion criteria by having plasma homocysteine levels at or above 12 μmol/l. They were randomized (1:1) to either active treatment (with cyanocobalamin 0.5 mg, folic acid 0.8 mg and pyridoxine 3.0 mg) q.d. or to a control arm with a cross over to active treatment after 12 months. Cognitive function was measured repeatedly during the trial, which ran for 24 months. We found a significant correlation between plasma neurofilament light protein and plasma homocysteine at screening (n = 124, r = 0.35, P < 0.0001). Plasma homocysteine levels decreased by 35% from a geometric mean of 15.7 μmol/l (95% confidence interval 14.7–16.7) to 10.3 μmol/l (95% confidence interval 9.3–11.3) in the active treatment arm between baseline and Month 12. No significant change was detected in the control arm during the same time period [geometric mean 15.2 (95% confidence interval 14.3–16.2) versus geometric mean 16.5 μmol/l (95% confidence interval 14.7–18.6)]. A significant difference in change in plasma homocysteine levels was seen between arms at 12 months [−40% (95% confidence interval −48 to −30%), P < 0.001]. However, no difference between arms was seen in either plasma neurofilament light protein levels [−6.5% (−20 to 9%), P = 0.39], or cognitive measures [−0.08 (−0.33 to 0.17), P = 0.53]. Our results do not support a vitamin B–dependent cause of the correlation between neurofilament light protein and homocysteine. Additional studies are needed to further elucidate this matter.

Lessons from the Cerebrospinal Fluid Analysis of HTLV-1-Infected Individuals: Biomarkers of Inflammation for HAM/TSP Development

HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a neurodegenerative disease that leads to motor impairment due to a chronic inflammatory process in the central nervous system (CNS). However, the HAM/TSP pathogenesis is not completely clear, and biomarkers to define the disease prognosis are still necessary. Thus, we aimed to identify biomarkers for HAM/TSP and potential mechanisms involved in disease development. To that end, the concentrations of VILIP-1, BDNF, VEGF, β-NGF, TGF-β1, fractalkine/CX3CL1, IL-6, IL-18, and TNF-α, and the soluble forms of TREM-1, TREM-2, and RAGE, were assessed using a multiplex bead-based immunoassay in paired cerebrospinal fluid (CSF) and serum samples from HAM/TSP patients (n = 20), asymptomatic HTLV-1 carriers (AC) (n = 13), and HTLV-1-seronegative individuals (n = 9), with the results analyzed according to the speed of HAM/TSP progression. HAM/TSP patients had elevated fractalkine in the serum but not in the CSF, particularly those with low neuroinflammatory activity (CSF/serum ratio of neopterin <1 and of CXCL10 < 2). HAM/TSP patients with normal CSF levels of neurofilament light chain (NfL) showed elevated β-NGF in serum, and serum BDNF levels were increased in HTLV-1-infected individuals, particularly in HTLV-1 AC. Both HTLV-1 AC and HAM/TSP patients had lower TGF-β1 levels in CSF compared to uninfected individuals, and HAM/TSP patients with active CNS inflammation showed higher CSF levels of IL-18, which correlated with markers of inflammation, neuronal death, and blood−brain-barrier permeability. Although none of the factors evaluated were associated with the speed of HAM/TSP progression, reduced TGF-β1 levels in CSF suggest that suppressive responses to control subclinical and/or active neurodegeneration are impaired, while increased CSF IL-18 indicates the involvement of inflammasome-mediated mechanisms in HAM/TSP development.

Correlation between CD4/CD8 ratio and neurocognitive performance during early HIV infection

INTRODUCTION

CD4/CD8 ratio is a marker of immune activation in HIV infection and has been associated with neurocognitive performance during chronic infection, but little is known about the early phases. The aim of this study was to examine the relationship between blood CD4/CD8 ratio and central nervous system endpoints in primary HIV infection (PHI) before and after antiretroviral treatment (ART).

METHODS

This was a retrospective analysis of the Primary Infection Stage CNS Events Study (PISCES) cohort. We longitudinally assessed blood and cerebrospinal fluid (CSF) markers of inflammation, immune activation and neuronal injury, and neuropsychological testing performance (NPZ4, an average of three motor and one processing speed tests, and a summarized total score, NPZ11, including also executive function, learning and memory) in ART-naïve participants enrolled during PHI. Spearman correlation and linear mixed models assessed the relationships between the trajectory of CD4/CD8 ratio over time and neurocognitive performance, blood and CSF markers of immune activation and neuronal injury.

RESULTS

In all, 109 PHI participants were enrolled. The mean CD4/CD8 ratio decreased with longer time from infection to starting treatment (p < 0.001). Every unit increase in NPZ4 score was independently associated with a 0.15 increase in CD4/CD8 ratio (95% CI: 0.002-0.29; p = 0.047), whereas no correlation was found between CD4/CD8 ratio and NPZ11. Among the cognitive domains, only a change in processing speed was correlated with CD4/CD8 ratio over time (p = 0.03). The trajectory of the CD4/CD8 ratio was negatively correlated with change in CSF neurofilament light chain (p = 0.04).

CONCLUSIONS

The trajectory of CD4/CD8 ratio was independently associated with motor/psychomotor speed performance, suggesting that immune activation is involved in brain injury during the early stages of the infection.

Neuropathogenesis of HIV-1: insights from across the spectrum of acute through long-term treated infection

This review outlines the neuropathogenesis of HIV, from initial HIV entry into the central nervous system (CNS) to chronic infection, focusing on key advancements in the last 5 years. Discoveries regarding acute HIV infection reveal timing and mechanisms of early HIV entry and replication in the CNS, early inflammatory responses, and establishment of genetically distinct viral reservoirs in the brain. Recent studies additionally explore how chronic HIV infection is maintained in the CNS, examining how the virus remains in a latent "hidden" state in diverse cells in the brain, and how this leads to sustained pathological inflammatory responses. Despite viral suppression with antiretroviral therapy, HIV can persist and even replicate in the CNS, and associate with ongoing neuropathology including CD8 + T-lymphocyte mediated encephalitis. Crucial investigation to advance our understanding of the immune mechanisms that both control viral infection and lead to pathological consequences in the brain is necessary to develop treatments to optimize long-term neurologic health in people living with HIV.

Cerebrospinal Fluid Viral Load Across the Spectrum of Untreated Human Immunodeficiency Virus Type 1 (HIV-1) Infection: A Cross-Sectional Multicenter Study

BACKGROUND

The aim of this large multicenter study was to determine variations in cerebrospinal fluid (CSF) HIV-RNA in different phases of untreated human immunodeficiency virus type 1 (HIV-1) infection and its associations with plasma HIV-RNA and other biomarkers.

METHODS

Treatment naive adults with available CSF HIV-RNA quantification were included and divided into groups representing significant disease phases. Plasma HIV-RNA, CSF white blood cell count (WBC), neopterin, and albumin ratio were included when available.

RESULTS

In total, 1018 patients were included. CSF HIV-RNA was in median (interquartile range [IQR]) 1.03 log10 (0.37-1.86) copies/mL lower than in plasma, and correlated with plasma HIV-RNA (r = 0.44, P < .01), neopterin concentration in CSF (r = 0.49, P < .01) and in serum (r = 0.29, P < .01), CSF WBC (r = 0.34, P < .01) and albumin ratio (r = 0.25, P < .01). CSF HIV-RNA paralleled plasma HIV-RNA in all groups except neuroasymptomatic patients with advanced immunodeficiency (CD4 < 200) and patients with HIV-associated dementia (HAD) or opportunistic central nervous system (CNS) infections. Patients with HAD had the highest CSF HIV-RNA (in median [IQR] 4.73 (3.84-5.35) log10 copies/mL). CSF > plasma discordance was found in 126 of 972 individuals (13%) and varied between groups, from 1% in primary HIV, 11% in neuroasymptomatic groups, up to 30% of patients with HAD.

CONCLUSIONS

Our study confirms previous smaller observations of variations in CSF HIV-RNA in different stages of HIV disease. Overall, CSF HIV-RNA was approximately 1 log10 copies/mL lower in CSF than in plasma, but CSF discordance was found in a substantial minority of subjects, most commonly in patients with HAD, indicating increasing CNS compartmentalization paralleling disease progression.

β-Amyloid-Dependent and -Independent Genetic Pathways Regulating CSF Tau Biomarkers in Alzheimer Disease

BACKGROUND AND OBJECTIVES

Abnormal metabolism of β-amyloid (Aβ) and soluble phosphorylated tau (P-tau), as well as neurodegeneration, are key components of Alzheimer disease (AD), but it is unclear how these different processes are related to genetic risk factors for AD.

METHODS

In the Swedish BioFINDER study, we tested associations between a priori defined polygenic risk scores (PRSs) for AD (excluding single-nucleotide polymorphism [SNP] within the APOE region in the main analysis) and biomarkers in CSF (total tau [T-tau] and P-tau181; Aβ1-38, Aβ1-40, Aβ1-42, and Aβ1-42/1-40; and neurofilament light [NfL]) in cognitively unimpaired (CU) individuals (n = 751), and in patients with mild cognitive impairment (MCI) (n = 212) and AD dementia (n = 150). Results were validated in the Alzheimer's Disease Neuroimaging Initiative data set with 777 individuals (AD = 119, MCI = 442, and CU = 216).

RESULTS

PRSs with SNPs significant at p < 5e-03 (∼1,742 variants) were associated with higher CSF P-tau181 (β = 0.13, p = 5.6e-05) and T-tau (β = 0.12, p = 4.3e-04). The associations between PRS and tau measures were partly attenuated but remained significant after adjusting for Aβ status. Aβ pathology mediated 37% of the effect of this PRS on tau levels. Aβ-dependent and Aβ-independent subsets of the PRS were identified and characterized. There were also associations between PRSs and CSF Aβ biomarkers with nominal significance, but not when corrected for multiple comparisons. There were no associations between PRSs and CSF NfL.

DISCUSSION

Genetic pathways implicated in causing AD are related to altered levels of soluble tau through both Aβ-dependent and Aβ-independent mechanisms, which may have relevance for anti-tau drug development.

The Role of Pannexin-1 Channels in HIV and NeuroHIV Pathogenesis

The human immunodeficiency virus-1 (HIV) enters the brain shortly after infection, leading to long-term neurological complications in half of the HIV-infected population, even in the current anti-retroviral therapy (ART) era. Despite decades of research, no biomarkers can objectively measure and, more importantly, predict the onset of HIV-associated neurocognitive disorders. Several biomarkers have been proposed; however, most of them only reflect late events of neuronal damage. Our laboratory recently identified that ATP and PGE2, inflammatory molecules released through Pannexin-1 channels, are elevated in the serum of HIV-infected individuals compared to uninfected individuals and other inflammatory diseases. More importantly, high circulating ATP levels, but not PGE2, can predict a decline in cognition, suggesting that HIV-infected individuals have impaired ATP metabolism and associated signaling. We identified that Pannexin-1 channel opening contributes to the high serological ATP levels, and ATP in the circulation could be used as a biomarker of HIV-associated cognitive impairment. In addition, we believe that ATP is a major contributor to chronic inflammation in the HIV-infected population, even in the anti-retroviral era. Here, we discuss the mechanisms associated with Pannexin-1 channel opening within the circulation, as well as within the resident viral reservoirs, ATP dysregulation, and cognitive disease observed in the HIV-infected population.

Blood biomarkers for HIV infection with focus on neurologic complications-A review

Although clinical examinations, neuroimaging, and cerebrospinal fluid analyses are the most important ways to evaluate the impact of HIV infection on the brain and in diagnosis of opportunistic infections, several blood biomarkers including HIV RNA concentrations, CD4 +T-cell count, and neurofilament light chain protein (NfL) concentration, along with tests for opportunistic infections can provide important information for clinical decisions.

Plasma Neurofilament Light Is Not Associated with Ongoing Neuroaxonal Injury or Cognitive Decline in Perinatally HIV Infected Adolescents: A Brief Report

Despite combination antiretroviral therapy (cART), adolescents with perinatally acquired human immunodeficiency virus (PHIV) exhibit cerebral injury and cognitive impairment. Plasma neurofilament light (pNfL) is a biomarker identified as a promising marker associated with neuroaxonal injury and cognitive impairment. To investigate whether cerebral injury in cART-treated PHIV adolescents is persistent, we longitudinally measured pNfL. We included 21 PHIV adolescents and 23 controls, matched for age, sex, ethnic origin and socio-economic status. We measured pNfL in both groups and CSF NfL in PHIV adolescents using a highly sensitive Single Molecule Array (Simoa) immunoassay. We compared pNfL between groups over time with a mean follow-up time of 4.6 years and assessed its association with MRI outcomes, cognitive function and HIV-related characteristics using linear mixed models. The median age was 17.5 years (15.5–20.7) and 16.4 years (15.8–19.6) at the second assessment for PHIV adolescents and controls, respectively. We found comparable pNfL (PHIV vs. controls) at the first (2.9 pg/mL (IQR 2.0–3.8) and 3.0 pg/mL (IQR 2.3–3.5), p = 0.499) and second assessment (3.3 pg/mL (IQR 2.5–4.1) and 3.0 pg/mL (IQR 2.5–3.7), p = 0.658) and observed no longitudinal change (coefficient; −0.19, 95% −0.5 to 0.1, p = 0.244). No significant associations were found between pNfL and HIV- or cART-related variables, MRI outcomes or cognitive function. We observed low CSF NfL concentrations at the baseline in PHIV adolescents (100.8 pg/mL, SD = 47.5). Our results suggest that there is no ongoing neuroaxonal injury in cART-treated PHIV adolescents and that the neuroaxonal injury is acquired in the past, emphasizing the importance of early cART to mitigate HIV-related neuroaxonal damage.

CSF markers of AD-related pathology relate specifically to memory impairment in older people with HIV: a pilot study

Given the co-occurrence of memory impairment in HIV-associated neurocognitive disorders (HAND) and amnestic mild cognitive impairment/Alzheimer's disease (aMCI/AD), biomarkers are needed that can disentangle these conditions among people with HIV (PWH). We assessed whether cerebrospinal fluid (CSF) markers of AD could help in this effort by determining their relationship to learning and memory deficits versus cognitive deficits more characteristic of HAND than aMCI/AD (processing speed and complex visual/motor coordination) among 31 older PWH. CSF amyloid-β42 phosphorylated-tau, amyloid-β40/amyloid-β42 and phosphorylated-tau/amyloid-β42 ratio related to learning/memory performance but not HAND-related deficits, suggesting that these biomarkers may have utility in disentangling aMCI/AD from HAND.

Correlation between cerebrospinal fluid and plasma neurofilament light protein in treated HIV infection: results from the COBRA study

Cerebrospinal fluid (CSF) neurofilament light protein (NfL) is a marker of central nervous system neuro-axonal injury. A novel, ultra-sensitive assay can determine plasma NfL. In untreated people-with-HIV (PWH), CSF and plasma NfL are strongly correlated. We aimed to assess this correlation in PWH on suppressive antiretroviral treatment (ART) and lifestyle-similar HIV-negative individuals enrolled into the COmorBidity in Relation to AIDS (COBRA) study. Differences in paired CSF (sandwich ELISA, UmanDiagnostics) and plasma (Simoa digital immunoassay, Quanterix™) NfL between PWH and HIV-negative participants were tested using Wilcoxon's test; associations were assessed using Pearson's correlation. CSF and plasma NfL, standardised to Z-scores, were included as dependent variables in linear regression models to identify factors independently associated with values in PWH and HIV-negative participants. Overall, 132 PWH (all with plasma HIV RNA < 50 copies/mL) and 79 HIV-negative participants were included. Neither CSF (median 570 vs 568 pg/mL, p = 0.37) nor plasma (median 10.7 vs 9.9 pg/mL, p = 0.15) NfL differed significantly between PWH and HIV-negative participants, respectively. CSF and plasma NfL correlated moderately, with no significant difference by HIV status (PWH: rho = 0.52; HIV-negative participants: rho = 0.47, p (interaction) = 0.63). In multivariable regression analysis, higher CSF NfL Z-score was statistically significantly associated with older age and higher CSF protein, and higher plasma NfL Z-score with older age, higher serum creatinine and lower bodyweight. In conclusion, in PWH on ART, the correlation between CSF and plasma NfL is moderate and similar to that observed in lifestyle-similar HIV-negative individuals. Consideration of renal function and bodyweight may be required when utilising plasma NfL.

Effect of antiretroviral treatment on blood-brain barrier integrity in HIV-1 infection

Background

Blood-brain barrier (BBB) injury is prevalent in patients with HIV-associated dementia (HAD) and is a frequent feature of HIV encephalitis. Signs of BBB damage are also sometimes found in neuroasymptomatic HIV-infected individuals without antiretroviral therapy (ART). The aim of this study was to investigate the integrity of the BBB before and after initiation of ART in both neuroasymptomatic HIV infection and in patients with HAD.

Methods

We determined BBB integrity by measuring cerebrospinal fluid (CSF)/plasma albumin ratios in archived CSF samples prior to and after initiation of ART in longitudinally-followed neuroasymptomatic HIV-1-infected individuals and patients with HAD. We also analyzed HIV RNA in blood and CSF, IgG Index, CSF WBC counts, and CSF concentrations of β2-micoglobulin, neopterin, and neurofilament light chain protein (NfL).

Results

We included 159 HIV-infected participants; 82 neuroasymptomatic individuals and 77 with HAD. All neuroasymptomatic individuals (82/82), and 10/77 individuals with HAD, were longitudinally followed with a median (interquartile range, IQR) follow-up of 758 (230–1752) days for the neuroasymptomatic individuals, and a median (IQR) follow-up of 241 (50–994) days for the individuals with HAD. Twelve percent (10/82) of the neuroasymptomatic individuals and 80% (8/10) of the longitudinally-followed individuals with HAD had elevated albumin ratios at baseline. At the last follow-up, 9% (7/82) of the neuroasymptomatic individuals and 20% (2/10) of the individuals with HAD had elevated albumin ratios. ART significantly decreased albumin ratios in both neuroasymptomatic individuals and in patients with HAD.

Conclusion

These findings indicate that ART improves and possibly normalizes BBB integrity in both neuroasymptomatic HIV-infected individuals and in patients with HAD.

Emerging Single-cell Approaches to Understand HIV in the Central Nervous System

Purpose of Review

This review highlights emerging single-cell sequencing methods relevant to translational studies of HIV in the central nervous system (CNS), summarizes limited single-cell studies of HIV in the CNS, and discusses opportunities for future HIV translational CNS studies.

Recent Findings

Innovative methods utilizing single-cell technologies have advanced the study of genomes, proteomes, transcriptomes, and epigenomes at an enhanced resolution and depth. Single-cell analyses of central nervous system tissue, including autopsy brain and CSF cells, may shed light on CNS perturbations in people living with HIV. New strategies can distinguish distinct molecular identifies of rare infected cells at single-cell level, suggesting an opportunity to uncloak the molecular identity of hidden HIV in the CNS reservoir.

Summary

Adoption of multimodal “omics” analyses to translational HIV studies and tissue compartments beyond blood will be critical to advancing our understanding of viral establishment, persistence, and eradication.

Increased immune activation and signs of neuronal injury in HIV-negative people on preexposure prophylaxis

OBJECTIVE

Persistent immune activation in the central nervous system and systemically are common in people living with HIV (PLHIV) despite antiretroviral therapy. It is not known whether this is generated by HIV replication or by other components such as coinfections and lifestyle-related factors.

DESIGN

The aim of this study was to determine the importance of different factors; it is crucial to find well matched HIV-negative controls. In this context, HIV-negative persons on preexposure prophylaxis (PrEP) may constitute a suitable control group to PLHIV with similar lifestyle-related factors.

METHODS

Cerebrospinal fluid (CSF) and blood were collected from 40 HIV-negative persons on PrEP and 20 controls without PrEP. Biomarkers of immune activation, blood--brain barrier (BBB) integrity and neuronal injury were analysed.

RESULTS

CSF and serum β2-microglobulin, serum neopterin and CSF neurofilament light protein were higher in persons on PrEP compared with controls. Furthermore, persons on PrEP had higher CSF/plasma albumin ratio, and matrix metalloproteinase-3 concentrations, indicating BBB dysfunction. Of persons on PrEP, 90% were cytomegalovirus (CMV)-positive compared to 65% of the controls. CMV-positive individuals as a group had higher levels of serum β2-microglobulin than CMV-negative individuals (P < 0.05). Drug users had higher serum β2-microglobulin compared to nonusers (P < 0.01).

CONCLUSION

HIV-negative persons on PrEP had higher levels of biomarkers for immune activation, BBB impairment and neuronal injury, compared with volunteers without PrEP. Moreover, serum β2-microglobulin was higher in CMV-positive than in CMV-negative individuals and in drug users compared with nonusers. These findings are important to consider when analysing immune activation and CNS injury in PLHIV, and emphasize the importance of appropriate controls.

Following the Clues: Usefulness of Biomarkers of Neuroinflammation and Neurodegeneration in the Investigation of HTLV-1-Associated Myelopathy Progression

Human T-lymphotropic virus type 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a neurodegenerative disease due to axonal damage of the corticospinal secondary to an inflammatory response against infected T-cells. In the present work, we aimed to evaluate biomarkers of neurodegeneration and neuroinflammation in the definition of HAM/TSP prognosis. Neurofilament light (NfL) and phosphorylated heavy (pNfH) chains, total Tau protein, cellular prion protein (PrPc), inflammatory chemokines, and neopterin were quantified in paired cerebrospinal fluid (CSF) and serum samples from HAM/TSP patients (n=21), HTLV-1 asymptomatic carriers (AC) (n=13), and HTLV-1 seronegative individuals with non-inflammatory non-degenerative neurological disease (normal-pressure hydrocephalus) (n=9) as a control group. HTLV-1 proviral load in peripheral blood mononuclear cells and the expression of chemokine receptors CCR4, CCR5, and CXCR3 in infected CD4+ T-cells (HTLV-1 Tax+ cells) were also assessed. CSF levels of Tau, NfL, and pNfH were similar between groups, but PrPc and neopterin were elevated in HAM/TSP patients. Most individuals in the control group and all HTLV-1 AC had CSF/serum neopterin ratio < 1.0, and two-thirds of HAM/TSP patients had ratio values > 1.0, which positively correlated with the speed of disease progression and pNfH levels, indicating active neuroinflammation. HAM/TSP patients showed high serum levels of CXCR3-binding chemokines (CXCL9, CXCL10, and CXCL11) and elevated CSF levels of CCL2, CCL3, CCL4, CCL17, CXCL5, CXCL10, and CXCL11. Indeed, CXCL10 concentration in CSF of HAM/TSP patients was 5.8-fold and 8.7-fold higher in than in HTLV-1 AC and controls, respectively, and correlated with CSF cell counts. HAM/TSP patients with typical/rapid disease progression had CSF/serum CXCL10 ratio > 1.0 and a higher frequency of CXCR3+Tax+CD4+ T-cells in blood, which indicated a positive gradient for the migration of infected cells and infiltration into the central nervous system. In conclusion, the slow progression of HAM/TSP abrogates the usefulness of biomarkers of neuronal injury for the disease prognosis. Thus, markers of inflammation provide stronger evidence for HAM/TSP progression, particularly the CSF/serum neopterin ratio, which may contribute to overcome differences between laboratory assays.

Blood-Brain Barrier Dysfunction in CNS Disorders and Putative Therapeutic Targets: An Overview

The blood-brain barrier (BBB) is a fundamental component of the central nervous system (CNS). Its functional and structural integrity is vital to maintain the homeostasis of the brain microenvironment by controlling the passage of substances and regulating the trafficking of immune cells between the blood and the brain. The BBB is primarily composed of highly specialized microvascular endothelial cells. These cells’ special features and physiological properties are acquired and maintained through the concerted effort of hemodynamic and cellular cues from the surrounding environment. This complex multicellular system, comprising endothelial cells, astrocytes, pericytes, and neurons, is known as the neurovascular unit (NVU). The BBB strictly controls the transport of nutrients and metabolites into brain parenchyma through a tightly regulated transport system while limiting the access of potentially harmful substances via efflux transcytosis and metabolic mechanisms. Not surprisingly, a disruption of the BBB has been associated with the onset and/or progression of major neurological disorders. Although the association between disease and BBB disruption is clear, its nature is not always evident, specifically with regard to whether an impaired BBB function results from the pathological condition or whether the BBB damage is the primary pathogenic factor prodromal to the onset of the disease. In either case, repairing the barrier could be a viable option for treating and/or reducing the effects of CNS disorders. In this review, we describe the fundamental structure and function of the BBB in both healthy and altered/diseased conditions. Additionally, we provide an overview of the potential therapeutic targets that could be leveraged to restore the integrity of the BBB concomitant to the treatment of these brain disorders.

Neurofilament Proteins as Biomarkers to Monitor Neurological Diseases and the Efficacy of Therapies

Biomarkers of neurodegeneration and neuronal injury have the potential to improve diagnostic accuracy, disease monitoring, prognosis, and measure treatment efficacy. Neurofilament proteins (NfPs) are well suited as biomarkers in these contexts because they are major neuron-specific components that maintain structural integrity and are sensitive to neurodegeneration and neuronal injury across a wide range of neurologic diseases. Low levels of NfPs are constantly released from neurons into the extracellular space and ultimately reach the cerebrospinal fluid (CSF) and blood under physiological conditions throughout normal brain development, maturation, and aging. NfP levels in CSF and blood rise above normal in response to neuronal injury and neurodegeneration independently of cause. NfPs in CSF measured by lumbar puncture are about 40-fold more concentrated than in blood in healthy individuals. New ultra-sensitive methods now allow minimally invasive measurement of these low levels of NfPs in serum or plasma to track disease onset and progression in neurological disorders or nervous system injury and assess responses to therapeutic interventions. Any of the five Nf subunits - neurofilament light chain (NfL), neurofilament medium chain (NfM), neurofilament heavy chain (NfH), alpha-internexin (INA) and peripherin (PRPH) may be altered in a given neuropathological condition. In familial and sporadic Alzheimer's disease (AD), plasma NfL levels may rise as early as 22 years before clinical onset in familial AD and 10 years before sporadic AD. The major determinants of elevated levels of NfPs and degradation fragments in CSF and blood are the magnitude of damaged or degenerating axons of fiber tracks, the affected axon caliber sizes and the rate of release of NfP and fragments at different stages of a given neurological disease or condition directly or indirectly affecting central nervous system (CNS) and/or peripheral nervous system (PNS). NfPs are rapidly emerging as transformative blood biomarkers in neurology providing novel insights into a wide range of neurological diseases and advancing clinical trials. Here we summarize the current understanding of intracellular NfP physiology, pathophysiology and extracellular kinetics of NfPs in biofluids and review the value and limitations of NfPs and degradation fragments as biomarkers of neurodegeneration and neuronal injury.

Neurochemical biomarkers to study CNS effects of COVID-19: a narrative review and synthesis

Neurological symptoms are frequently reported in patients suffering from COVID‐19. Common CNS‐related symptoms include anosmia, caused by viral interaction with either neurons or supporting cells in nasal olfactory tissues. Diffuse encephalopathy is the most common sign of CNS dysfunction, which likely results from the CNS consequences of the systemic inflammatory syndrome associated with severe COVID‐19. Additionally, microvascular injuries and thromboembolic events likely contribute to the neurologic impact of acute COVID‐19. These observations are supported by evidence of CNS immune activation in cerebrospinal fluid (CSF) and in autopsy tissue, along with the detection of microvascular injuries in both pathological and neuroimaging studies. The frequent occurrence of thromboembolic events in patients with COVID‐19 has generated different hypotheses, among which viral interaction with perivascular cells is particularly attractive, yet unproven. A distinguishing feature of CSF findings in SARS‐CoV‐2 infection is that clinical signs characteristic of neurotropic viral infections (CSF pleocytosis and blood–brain barrier injury) are mild or absent. Moreover, virus detection in CSF is rare and often of uncertain significance. In this review, we provide an overview of the neurological impact that occurs in the acute phase of COVID‐19, and the role of CSF biomarkers in the clinical management and research to better treat and understand the disease. In addition to aiding as diagnostic and prognostic tools during acute infection, the use of comprehensive and well‐characterized CSF and blood biomarkers will be vital in understanding the potential impact on the CNS in the rapidly increasing number of individuals recovering from COVID‐19.

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.