Amyloid and tau cerebrospinal fluid biomarkers in HIV infection

The Physiological Roles of Amyloid-β Peptide Hint at New Ways to Treat Alzheimer's Disease

Amyloid-ß (Aß) is best known as the misfolded peptide that is involved in the pathogenesis of Alzheimer's disease (AD), and it is currently the primary therapeutic target in attempts to arrest the course of this disease. This notoriety has overshadowed evidence that Aß serves several important physiological functions. Aß is present throughout the lifespan, it has been found in all vertebrates examined thus far, and its molecular sequence shows a high degree of conservation. These features are typical of a factor that contributes significantly to biological fitness, and this suggestion has been supported by evidence of functions that are beneficial for the brain. The putative roles of Aß include protecting the body from infections, repairing leaks in the blood-brain barrier, promoting recovery from injury, and regulating synaptic function. Evidence for these beneficial roles comes from in vitro and in vivo studies, which have shown that the cellular production of Aß rapidly increases in response to a physiological challenge and often diminishes upon recovery. These roles are further supported by the adverse outcomes of clinical trials that have attempted to deplete Aß in order to treat AD. We suggest that anti-Aß therapies will produce fewer adverse effects if the known triggers of Aß deposition (e.g., pathogens, hypertension, and diabetes) are addressed first.

Differentiating HIV-Associated Neurocognitive Disorders From Alzheimer's Disease: an Emerging Issue in Geriatric NeuroHIV

PURPOSE OF REVIEW

The purpose of this review was to examine characteristics that may distinguish HIV-associated neurocognitive disorder (HAND) from early Alzheimer's disease (AD).

RECENT FINDINGS

Cerebrospinal fluid (CSF) AD biomarkers are perturbed in HIV, yet these alterations may be limited to settings of advanced dementia or unsuppressed plasma HIV RNA. Neuropsychological testing will require extensive batteries to maximize utility. Structural imaging is limited for early AD detection in the setting of HIV, but proper studies are absent. While positron-emission tomography (PET) amyloid imaging has altered the landscape of differential diagnosis for age-associated neurodegenerative disorders, costs are prohibitive. Risk for delayed AD diagnosis in the aging HIV-infected population is now among the most pressing issues in geriatric neuroHIV. While clinical, imaging, and biomarker characterizations of AD are extensively defined, fewer data define characteristics of HIV-associated neurocognitive disorder in the setting of suppressed plasma HIV RNA. Data needed to inform the phenotype of AD in the setting of HIV are equally few.

Biomarkers of neuronal injury and amyloid metabolism in the cerebrospinal fluid of patients infected with HIV-1 subtypes B and C

Based on prior reports that the HIV-1 Tat protein modulates amyloid-beta (Aβ) metabolism, this study aimed to compare CSF neural injury biomarkers between 27 patients with HIV subtype B, 26 patients with HIV subtype C, 18 healthy HIV-negative controls, and 24 patients with Alzheimer's disease (AD). Immunoassays were used to measure soluble amyloid precursor protein α and β (sAPPα, sAPPβ), Aβ oligomers 38, 40, 42, and Aβ-total; phosphorylated tau (P-tau181), and total tau (T-tau). Comparisons between HIV(+) and HIV(-) (including AD) were adjusted by linear regression for gender and age; HIV subtype comparisons were adjusted for nadir CD4 and plasma viral load suppression. The p values were corrected for multiple testing with the Benjamini-Hochberg procedure. CSF Aβ-42 and Hulstaert (P-tau181) index were lower in HIV1-C than B (p = 0.03, and 0.049 respectively); subtypes did not differ on other CSF biomarkers or ratios. Compared to AD, HIV(+) had lower CSF levels of T-tau, P-tau181 (p < 0.001), and sAPPα (p = 0.041); HIV(+) had higher CSF Aβ-42 (p = 0.002) and higher CSF indexes: [Aß-42/(240 + 1.18 T-tau)], P-tau181/Aβ-42, T-tau/Aβ-42, P-tau181/T-tau, sAPPα/β (all p ≤ 0.01) than AD. Compared to HIV(-), HIV(+) had lower CSF Aβ-42, and T-tau (all p ≤ 0.004). As conclusion, amyloid metabolism was influenced by HIV infection in a subtype-dependent manner. Aß-42 levels were lower in HIV1-C than B, suggesting that there may be greater deposition of Aß-42 in HIV1-C. These findings are supported by CSF Hulstaert (P-tau181) index. Differences between HIV and AD in the patterns of Aß and Tau biomarkers suggest that CNS HIV infection and AD may not share some of same mechanisms of neuronal injury.

HIV/neuroAIDS biomarkers

HIV infection often causes neurological symptoms including cognitive and motor dysfunction, which have been collectively termed HIV/neuroAIDS. Neuropsychological assessment and clinical symptoms have been the primary diagnostic criteria for HIV/neuroAIDS, even for the mild cognitive and motor disorder, the most prevalent form of HIV/neuroAIDS in the era of combination antiretroviral therapy. Those performance-based assessments and symptoms are generally descriptive and do not have the sensitivity and specificity to monitor the diagnosis, progression, and treatment response of the disease when compared to objective and quantitative laboratory-based biological markers, or biomarkers. In addition, effects of demographics and comorbidities such as substance abuse, psychiatric disease, nutritional deficiencies, and co-infection on HIV/neuroAIDS could be more readily determined using biomarkers than using neuropsychological assessment and clinical symptoms. Thus, there have been great efforts in identification of HIV/neuroAIDS biomarkers over the past two decades. The need for reliable biomarkers of HIV/neuroAIDS is expected to increase as the HIV-infected population ages and their vulnerability to neurodegenerative diseases, particularly Alzheimer's disease increases. Currently, three classes of HIV/neuroAIDS biomarkers are being pursued to establish objective laboratory-based definitions of HIV-associated neurologic injury: cerebrospinal fluid biomarkers, blood biomarkers, and neuroimaging biomarkers. In this review, we will focus on the current knowledge in the field of HIV/neuroAIDS biomarker discovery.

Blood neuron-derived exosomes as biomarkers of cognitive impairment in HIV

OBJECTIVE

To investigate proteins associated with neuronal damage in plasma neuron-derived exosomes (NDE) of HIV-infected study participants as a liquid biomarker for cognitive impairment.

METHODS

Plasma NDE were isolated using precipitation and immunoadsorption with antibody to a cell surface-specific neuronal marker. Total exosomes and NDE were enumerated, characterized, and proteins extracted and targets quantified by ELISA.

RESULTS

Plasma NDE from 23 HIV seropositive individuals of which 11 had mild cognitive impairment, and 12 HIV seronegative controls of which three had cognitive impairment were isolated. NDE were enriched for the neuronal markers neurofilament light (NF-L) and synaptophysin (SYP). Neuropsychologically impaired individuals had fewer NDE compared with neuropsychologically normal study participants. NDE from neuropsychologically impaired study participants had significantly higher levels of high-mobility group box 1 (HMGB1), NF-L, and amyloid β proteins compared with neuropsychologically normal individuals. NDE HMGB1 protein significantly decreased with age in HIV-infected individuals.

CONCLUSION

Plasma NDE were altered in several ways in HIV infection. Elevated HMGB1, NF-L, and amyloid β proteins could distinguish cognitive impairment. NDE contents reflect neuronal health in 'real time' and may be useful for following cognitive impairment and response to therapy in HIV infection.

Lower CSF Aβ is Associated with HAND in HIV-Infected Adults with a Family History of Dementia

BACKGROUND

Both family history of dementia (FHD) and lower levels of Aβ-42 are indepentently associated with worse neurocognitive functioning in HIVinfected patients.

OBJECTIVE

To examine the relationships between cerebrospinal fluid (CSF) Aβ-42 and FHD with HIV-associated neurocognitive disorders (HAND).

METHODS

One hundred eighty-three HIV+ adults underwent neuropsychological and neuromedical assessments, and determination of CSF Aβ-42 concentration and FHD (defined as a self-reported first or second-degree relative with a dementia diagnosis). Univariate analyses and multivariable logistic regressions were used.

RESULTS

FHD was not associated with HAND (p = 0.24); however, CSF Aβ-42 levels were lower (p = 0.03) in the HAND group, but were not associated with FHD (p = 0.89). Multivariable models showed a main effect of CSF Aβ-42 (p = 0.03) and a trend-level (p = 0.06) interaction between FHD and CSF Aβ-42, such that lower CSF Aβ-42 was associated with HAND in those with FHD (p < 0.01) compared to those without FHD (p = 0.83). An analysis in those with follow-up data showed that higher baseline CSF Aβ-42 was associated with lower risk of neurocognitive decline (p = 0.02). While we did not find an FHD X CSF Aβ-42 interaction (p = 0.83), when analyses were stratified by FHD, lower CSF Aβ-42 was associated at the trend-level with neurocognitive decline in the FHD group (p = 0.08) compared to the no FHD group (p = 0.15).

CONCLUSION

FHD moderates the relationship between of CSF Aβ-42 and HAND. The findings highlight the complexities in interpreting the relationships between biomarkers of age-related neurodegeneration and HAND.

Neurofilament light chain protein as a marker of neuronal injury: review of its use in HIV-1 infection and reference values for HIV-negative controls

INTRODUCTION

Several CSF biomarkers of neuronal injury have been studied in people living with HIV. At this time, the most useful is the light subunit of the neurofilament protein (NFL). This major structural component of myelinated axons is essential to maintain axonal caliber and to facilitate effective nerve conduction. CSF concentrations of NFL provide a sensitive marker of CNS injury in a number of neurological diseases, including HIV-related neuronal injury. Areas Covered: In this review, the authors describe CSF NFL concentrations across the spectrum of HIV-infection, from its early acute phase to severe immunosuppression, with and without neurological conditions, and with and without antiretroviral treatment (n = 516). Furthermore, in order to provide more precise estimates of age-related upper limits of CSF NFL concentrations, the authors present data from a large number (n = 359) of HIV-negative controls. Expert Commentary: Recently a new ultrasensitive diagnostic assay for quantification of NFL in plasma has been developed, providing a convenient way to assess neuronal damage without having to perform a lumbar puncture. This review also considers our current knowledge of plasma NFL in HIV CNS infection.

Plasma soluble CD163 is associated with postmortem brain pathology in human immunodeficiency virus infection

OBJECTIVE

Higher plasma soluble cluster of differentiation (CD)163 (sCD163), shed by monocytes and macrophages, correlates with neurocognitive impairment in HIV infection. We hypothesized that higher antemortem plasma or cerebrospinal fluid (CSF) sCD163 would be associated with greater postmortem neurodegeneration and/or microgliosis.

DESIGN

Retrospective, postmortem observational study.

METHODS

We measured sCD163 levels in antemortem plasma (n = 54) and CSF (n = 32) samples from 74 HIV-seropositive participants (median 5 months before death) who donated their brains to research at autopsy. Postmortem, we quantified markers of synaptodendritic damage (microtubule-associated protein 2, synaptophysin), microgliosis [human leukocyte antigen DR (HLA-DR), ionized calcium-binding adaptor molecule 1], astrocytosis (glial fibrillary acidic protein), and impaired protein clearance (β-amyloid) in frontal cortex, hippocampus, putamen, and internal capsule. Multivariable least-squares regression was used to evaluate the association between plasma or CSF sCD163 and histological measures, correcting for multiple comparisons.

RESULTS

Higher plasma sCD163 was associated with lower microtubule-associated protein 2 in frontal cortex [B = -0.23, 95% confidence interval (CI) -0.41 to -0.06, P = 0.04], putamen (B = 0.32, 95% CI -0.52 to -0.12, P = 0.02), and hippocampus (B = -0.23, 95% CI -0.35 to -0.10, P = 0.01), and with lower synaptophysin in hippocampus (B = -0.25, 95% CI -0.42 to -0.03, P = 0.02) but not putamen or frontal cortex (P > 0.05). Higher plasma sCD163 was associated with higher HLA-DR in putamen (B = 0.17, 95% CI 0.08 to 0.26, P = 0.008). CSF sCD163 was not associated with any histological measure (P > 0.05).

CONCLUSION

Higher plasma sCD163 in life is associated with greater synaptodendritic damage and microglial activation in cortical and subcortical brain regions.

Ex vivo 18O-labeling mass spectrometry identifies a peripheral amyloid β clearance pathway

Background

Proteolytic degradation of amyloid β (Aβ) peptides has been intensely studied due to the central role of Aβ in Alzheimer’s disease (AD) pathogenesis. While several enzymes have been shown to degrade Aβ peptides, the main pathway of Aβ degradation in vivo is unknown. Cerebrospinal fluid (CSF) Aβ42 is reduced in AD, reflecting aggregation and deposition in the brain, but low CSF Aβ42 is, for unknown reasons, also found in some inflammatory brain disorders such as bacterial meningitis.

Method

Using ¹⁸O-labeling mass spectrometry and immune-affinity purification, we examined endogenous proteolytic processing of Aβ in human CSF.

Results

The Aβ peptide profile was stable in CSF samples from healthy controls but in CSF samples from patients with bacterial meningitis, showing increased leukocyte cell count, ¹⁸O-labeling mass spectrometry identified proteolytic activities degrading Aβ into several short fragments, including abundant Aβ1–19 and 1–20. After antibiotic treatment, no degradation of Aβ was detected. In vitro experiments located the source of the proteolytic activity to blood components, including leukocytes and erythrocytes, with insulin-degrading enzyme as the likely protease. A recombinant version of the mid-domain anti-Aβ antibody solanezumab was found to inhibit insulin-degrading enzyme-mediated Aβ degradation.

Conclusion

¹⁸O labeling-mass spectrometry can be used to detect endogenous proteolytic activity in human CSF. Using this technique, we found an enzymatic activity that was identified as insulin-degrading enzyme that cleaves Aβ in the mid-domain of the peptide, and could be inhibited by a recombinant version of the mid-domain anti-Aβ antibody solanezumab.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-017-0152-5) contains supplementary material, which is available to authorized users.

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

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

PET brain imaging in HIV-associated neurocognitive disorders (HAND) in the era of combination antiretroviral therapy

Effective combination antiretroviral therapy (cART) has lead to a significant reduction in the prevalence and incidence of central nervous system (CNS) HIV-associated brain disease, particularly CNS opportunistic infections and HIV encephalitis. Despite this, cognitive deficits in people living with HIV, also known as HIV-associated neurocognitive disorders (HAND) have become more prevalent in recent years. The pathogenesis of HAND is likely to be multifactorial, however recent evidence suggests that brain microglial activation is the most likely pathogenic mechanism. Recent developments in positron emission tomography (PET) brain neuroimaging using novel brain radioligands targeting a variety of physiological changes in the brains of HIV-positive individuals have improved our understanding of the mechanisms associated with the development of HAND. This review will highlight recent PET brain neuroimaging studies in the cART era, focusing on physiological and neurochemical changes associated with HAND in people living with HIV.

An Overview of Human Immunodeficiency Virus Type 1-Associated Common Neurological Complications: Does Aging Pose a Challenge?

With increasing survival of patients infected with human immunodeficiency virus type 1 (HIV-1), the manifestation of heterogeneous neurological complications is also increasing alarmingly in these patients. Currently, more than 30% of about 40 million HIV-1 infected people worldwide develop central nervous system (CNS)-associated dysfunction, including dementia, sensory, and motor neuropathy. Furthermore, the highly effective antiretroviral therapy has been shown to increase the prevalence of mild cognitive functions while reducing other HIV-1-associated neurological complications. On the contrary, the presence of neurological disorder frequently affects the outcome of conventional HIV-1 therapy. Although, both the children and adults suffer from the post-HIV treatment-associated cognitive impairment, adults, especially depending on the age of disease onset, are more prone to CNS dysfunction. Thus, addressing neurological complications in an HIV-1-infected patient is a delicate balance of several factors and requires characterization of the molecular signature of associated CNS disorders involving intricate cross-talk with HIV-1-derived neurotoxins and other cellular factors. In this review, we summarize some of the current data supporting both the direct and indirect mechanisms, including neuro-inflammation and genome instability in association with aging, leading to CNS dysfunction after HIV-1 infection, and discuss the potential strategies addressing the treatment or prevention of HIV-1-mediated neurotoxicity.

No support for premature central nervous system aging in HIV-1 when measured by cerebrospinal fluid phosphorylated tau (p-tau)

BACKGROUND

The prevalence of neurocognitive deficits are reported to be high in HIV-1 positive patients, even with suppressive antiretroviral treatment, and it has been suggested that HIV can cause accelerated aging of the brain. In this study we measured phosphorylated tau (p-tau) in cerebrospinal fluid (CSF) as a potential marker for premature central nervous system (CNS) aging. P-tau increases with normal aging but is not affected by HIV-associated neurocognitive disorders.

METHODS

With a cross-sectional retrospective design, p-tau, total tau (t-tau), neopterin and HIV-RNA were measured in CSF together with plasma HIV-RNA and blood CD4⁺ T-cells of 225 HIV-infected patients <50 y of age, subdivided into 3 groups: untreated neuroasymptomatic (NA) (n = 145), on suppressive antiretroviral treatment (cART) (n = 49), and HIV-associated dementia (HAD) (n = 31). HIV-negative healthy subjects served as controls (n = 79).

RESULTS

P-tau was not significantly higher in any HIV-infected group compared to HIV-negative controls. Significant increases in t-tau were found as expected in patients with HAD compared to NA, cART, and control groups (p < 0.001 ).

CONCLUSIONS

P-tau was not higher in HIV-infected patients compared to uninfected controls, thus failing to support a role for premature or accelerated brain aging in HIV infection.

Cerebrospinal Fluid from Alzheimer's Disease Patients Contains Fungal Proteins and DNA

The identification of biomarkers for Alzheimer's disease is important for patient management and to assess the effectiveness of clinical intervention. Cerebrospinal fluid (CSF) biomarkers constitute a powerful tool for diagnosis and monitoring disease progression. We have analyzed the presence of fungal proteins and DNA in CSF from AD patients. Our findings reveal that fungal proteins can be detected in CSF with different anti-fungal antibodies using a slot-blot assay. Additionally, amplification of fungal DNA by PCR followed by sequencing distinguished several fungal species. The possibility that these fungal macromolecules could represent AD biomarkers is discussed.

Sex differences in soluble markers vary before and after the initiation of antiretroviral therapy in chronically HIV-infected individuals

OBJECTIVE

To evaluate differences in soluble inflammatory markers between chronically HIV-infected men and women, with or without cognitive impairment, and in response to treatment.

DESIGN

Soluble biomarkers were measured in cryopreserved plasma and cerebrospinal fluid (CSF) of 60 treatment-naïve individuals (25 men and 35 women) with chronic HIV infection and 18 HIV-uninfected controls (9 men and 9 women) from Thailand. Following enrollment, participants began combination antiretroviral therapy and were evaluated for expression of these markers after 48 weeks.

METHODS

Plasma and CSF levels of 19 soluble biomarkers (IFN-γ, TNFα, TNF-RII, IL-1α, IL-1β, IL-4, IL-5, IL-6, IL-8, IL-10, IL-12p70, IL-15, MCP-1, t-Tau, IP-10, neopterin, IFNα, I-FABP, and sCD14) were measured using either a multiparameter or standard ELISA assay.

RESULTS

Prior to combination antiretroviral therapy, women with impaired cognition had elevated levels of neopterin and TNF-RII compared with women with normal cognition in both the plasma and CSF; however, levels did not differ between cognitively impaired or normal men. In a secondary outcome-hypothesis generating analysis, sex differences were also pronounced in plasma levels of MCP-1, IL-10, I-FABP, and sCD14 in response to treatment. Neopterin, IP-10, TNFα, TNF-RII, IFNα, MCP-1, IL-8, I-FABP, and sCD14 plasma levels remained elevated following 48 weeks of therapy in both sexes compared with uninfected controls.

CONCLUSION

We provide evidence of sustained immune activation after 48 weeks of treatment and identify possible sex differences in biomarkers previously linked to cognitive impairment, chronic inflammation, and gut integrity that may contribute to immunological differences between sexes in relationship to disease progression and response to therapy.

Cerebrospinal Fluid Biomarkers of Simian Immunodeficiency Virus Encephalitis : CSF Biomarkers of SIV Encephalitis

Antiretroviral therapy has led to increased survival of HIV-infected patients but also increased prevalence of HIV-associated neurocognitive disorders. We previously identified YKL40 as a potential cerebrospinal fluid (CSF) biomarker of lentiviral central nervous system (CNS) disease in HIV-infected patients and in the macaque model of HIV encephalitis. The aim of this study was to define the specificity and sensitivity along with the predictive value of YKL40 as a biomarker of encephalitis and to assess its relationship to CSF viral load. CSF YKL40 and SIV RNA concentrations were analyzed over the course of infection in 19 SIV-infected pigtailed macaques and statistical analyses were performed to evaluate the relationship to encephalitis. Using these relationships, CSF alterations of 31 neuroimmune markers were studied pre-infection, during acute and asymptomatic infection, at the onset of encephalitis, and at necropsy. YKL40 CSF concentrations above 1122 ng/ml were found to be a specific and sensitive biomarker for the presence of encephalitis and were highly correlated with CSF viral load. Macaques that developed encephalitis had evidence of chronic CNS immune activation during early, asymptomatic, and end stages of infection. At the onset of encephalitis, CSF demonstrated a rise of neuroimmune markers associated with macrophage recruitment, activation and interferon response. CSF YKL40 concentration and viral load are valuable biomarkers to define the onset of encephalitis. Chronic CNS immune activation precedes the development of encephalitis while some responses suggest protection from CNS lentiviral disease.

Neurometabolite Alterations Associated With Cognitive Performance in Perinatally HIV-Infected Children

Despite treatment with combination antiretroviral therapy (cART), cognitive impairment is still observed in perinatally HIV-infected children. We aimed to evaluate potential underlying cerebral injury by comparing neurometabolite levels between perinatally HIV-infected children and healthy controls. This cross-sectional study evaluated neurometabolites, as measured by Magnetic Resonance Spectroscopy (MRS), in perinatally HIV-infected children stable on cART (n = 26) and healthy controls (n = 36).Participants were included from a cohort of perinatally HIV-infected children and healthy controls, matched group-wise for age, gender, ethnicity, and socio-economic status. N-acetylaspartate (NAA), glutamate (Glu), myo-inositol (mI), and choline (Cho) levels were studied as ratios over creatine (Cre). Group differences and associations with HIV-related parameters, cognitive functioning, and neuronal damage markers (neurofilament and total Tau proteins) were determined using age-adjusted linear regression analyses.HIV-infected children had increased Cho:Cre in white matter (HIV-infected = 0.29 ± 0.03; controls = 0.27 ± 0.03; P value = 0.045). Lower nadir CD4+ T-cell Z-scores were associated with reduced neuronal integrity markers NAA:Cre and Glu:Cre. A Centers for Disease Control and Prevention (CDC) stage C diagnosis was associated with higher glial markers Cho:Cre and mI:Cre. Poorer cognitive performance was mainly associated with higher Cho:Cre in HIV-infected children, and with lower NAA:Cre and Glu:Cre in healthy controls. There were no associations between neurometabolites and neuronal damage markers in blood or CSF.Compared to controls, perinatally HIV-infected children had increased Cho:Cre in white matter, suggestive of ongoing glial proliferation. Levels of several neurometabolites were associated with cognitive performance, suggesting that MRS may be a useful method to assess cerebral changes potentially linked to cognitive outcomes.

Cerebrospinal fluid analysis in the HIV infection and compartmentalization of HIV in the central nervous system

The nervous system plays an important role in HIV infection. The purpose of this review is to discuss the indications for cerebrospinal fluid (CSF) analysis in HIV infection in clinical practice. CSF analysis in HIV infection is indicated for the diagnosis of opportunistic infections and co-infections, diagnosis of meningitis caused by HIV, quantification of HIV viral load, and analysis of CNS HIV compartmentalization. Although several CSF biomarkers have been investigated, none are clinically applicable. The capacity of HIV to generate genetic diversity, in association with the constitutional characteristics of the CNS, facilitates the generation of HIV quasispecies in the CNS that are distinct from HIV in the systemic circulation. CSF analysis has a well-defined and valuable role in the diagnosis of CNS infections in HIV/AIDS patients. Further research is necessary to establish a clinically applicable biomarker for the diagnosis of HIV-associated neurocognitive disorders.

The cerebrospinal fluid biomarker profile in an HIV-infected subject with Alzheimer's disease

It is a challenge to differentiate between HIV-associated neurocognitive disorders (HAND) and other types of neurocognitive disease in the ageing HIV-infected population. Here we describe a 63 year old HIV-infected woman who had a history, neuropsychological test result, and PET examination consistent with characteristic Alzheimer’s disease (AD). The cerebrospinal fluid (CSF) biomarker profile was analogous to the profile typically found in AD in HIV-negative patients with increased t-tau and p-tau, a decreased level of Aβ42 and normal levels of CSF neurofilament light protein and sAPPα and sAPPβ, distinctly different from findings in HIV-associated dementia (HAD). Assessment of CSF biomarkers may be a valuable tool for clinicians to distinguish between HAD and AD.

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

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

APOE ε4 moderates abnormal CSF-abeta-42 levels, while neurocognitive impairment is associated with abnormal CSF tau levels in HIV+ individuals - a cross-sectional observational study

Background

Cerebrospinal fluid (CSF) biomarkers Aβ1-42, t-tau and p-tau have a characteristic pattern in Alzheimer’s Disease (AD). Their roles in HIV-associated neurocognitive disorder (HAND) remains unclear.

Methods

Adults with chronic treated HIV disease were recruited (n = 43, aged 56.7 ± 7.9; 32% aged 60+; median HIV duration 20 years, >95% plasma and CSF HIV RNA <50 cp/mL, on cART for a median 24 months). All underwent standard neuropsychological testing (61% had HAND), APOE genotyping (30.9% carried APOE ε4 and 7.1% were ε4 homozygotes) and a lumbar puncture. Concentrations of Aβ1-42, t-tau and p-tau were assessed in the CSF using commercial ELISAs. Current neurocognitive status was defined using the continuous Global Deficit Score, which grades impairment in clinically relevant categories. History of HAND was recorded. Univariate correlations informed multivariate models, which were corrected for nadir CD4-T cell counts and HIV duration.

Results

Carriage of APOE ε4 predicted markedly lower levels of CSF Aβ1-42 in univariate (r = -.50; p = .001) and multivariate analyses (R² = .25; p < .0003). Greater levels of neurocognitive impairment were associated with higher CSF levels of p-tau in univariate analyses (r = .32; p = .03) and multivariate analyses (R² = .10; p = .03). AD risk prediction cut-offs incorporating all three CSF biomarkers suggested that 12.5% of participants had a high risk for AD. Having a CSF-AD like profile was more frequent in those with current (p = .05) and past HIV-associated dementia (p = .03).

Conclusions

Similarly to larger studies, APOE ε4 genotype was not directly associated with HAND, but moderated CSF levels of Aβ1-42 in a minority of participants. In the majority of participants, increased CSF p-tau levels were associated with current neurocognitive impairment. Combined CSF biomarker risk for AD in the current HIV+ sample is more than 10 times greater than in the Australian population of the same age. Larger prospective studies are warranted.

Electronic supplementary material

The online version of this article (doi:10.1186/s12883-015-0298-0) contains supplementary material, which is available to authorized users.

Amyloid biomarkers in Alzheimer's disease

Aggregation of amyloid-β (Aβ) into oligomers, fibrils, and plaques is central in the molecular pathogenesis of Alzheimer's disease (AD), and is the main focus of AD drug development. Biomarkers to monitor Aβ metabolism and aggregation directly in patients are important for further detailed study of the involvement of Aβ in disease pathogenesis and to monitor the biochemical effect of drugs targeting Aβ in clinical trials. Furthermore, if anti-Aβ disease-modifying drugs prove to be effective clinically, amyloid biomarkers will be of special value in the clinic to identify patients with brain amyloid deposition at risk for progression to AD dementia, to enable initiation of treatment before neurodegeneration is too severe, and to monitor drug effects on Aβ metabolism or pathology to guide dosage. Two types of amyloid biomarker have been developed: Aβ-binding ligands for use in positron emission tomography (PET) and assays to measure Aβ42 in cerebrospinal fluid (CSF). In this review, we present the rationales behind these biomarkers and compare their ability to measure Aβ plaque load in the brain. We also review possible shortcomings and the need of standardization of both biomarkers, as well as their implementation in the clinic.

Activation of latent human immunodeficiency virus by the histone deacetylase inhibitor panobinostat: a pilot study to assess effects on the central nervous system

In a substudy of a clinical trial, we assessed whether activation of latent human immunodeficiency virus (HIV) by the histone deacetylase inhibitor panobinostat had detrimental effects on the central nervous system (CNS). Adults infected with HIV received oral panobinostat 20 mg 3 times per week every other week for 8 weeks. In cerebrospinal fluid (CSF), we assayed panobinostat concentration, HIV RNA, and the level of neuroinflammatory or degenerative biomarkers in 11 individuals before and during study therapy. Neither panobinostat nor HIV RNA was detected in CSF. In addition, there was no change from baseline in CSF biomarkers. Thus, panobinostat administration was not associated with CNS adverse effects as assessed by CSF biomarkers.

Mechanisms of HIV-1 Tat neurotoxicity via CDK5 translocation and hyper-activation: role in HIV-associated neurocognitive disorders

The advent of more effective antiretroviral therapies has reduced the frequency of HIV dementia, however the prevalence of milder HIV associated neurocognitive disorders [HAND] is actually rising. Neurodegenerative mechanisms in HAND might include toxicity by secreted HIV-1 proteins such as Tat, gp120 and Nef that could activate neuro-inflammatory pathways, block autophagy, promote excitotoxicity, oxidative stress, mitochondrial dysfunction and dysregulation of signaling pathways. Recent studies have shown that Tat could interfere with several signal transduction mechanisms involved in cytoskeletal regulation, cell survival and cell cycle re-entry. Among them, Tat has been shown to hyper-activate cyclin-dependent kinase [CDK] 5, a member of the Ser/Thr CDKs involved in cell migration, angiogenesis, neurogenesis and synaptic plasticity. CDK5 is activated by binding to its regulatory subunit, p35 or p39. For this manuscript we review evidence showing that Tat, via calcium dysregulation, promotes calpain-1 cleavage of p35 to p25, which in turn hyper-activates CDK5 resulting in abnormal phosphorylation of downstream targets such as Tau, collapsin response mediator protein-2 [CRMP2], doublecortin [DCX] and MEF2. We also present new data showing that Tat interferes with the trafficking of CDK5 between the nucleus and cytoplasm. This results in prolonged presence of CDK5 in the cytoplasm leading to accumulation of aberrantly phosphorylated cytoplasmic targets [e.g.: Tau, CRMP2, DCX] that impair neuronal function and eventually lead to cell death. Novel therapeutic approaches with compounds that block Tat mediated hyper-activation of CDK5 might be of value in the management of HAND.

Cerebrospinal fluid (CSF) neuronal biomarkers across the spectrum of HIV infection: hierarchy of injury and detection

The character of central nervous system (CNS) HIV infection and its effects on neuronal integrity vary with evolving systemic infection. Using a cross-sectional design and archived samples, we compared concentrations of cerebrospinal fluid (CSF) neuronal biomarkers in 143 samples from 8 HIV-infected subject groups representing a spectrum of untreated systemic HIV progression and viral suppression: primary infection; four groups of chronic HIV infection neuroasymptomatic (NA) subjects defined by blood CD4+ T cells of >350, 200–349, 50–199, and <50 cells/µL; HAD; treatment-induced viral suppression; and ‘elite’ controllers. Samples from 20 HIV-uninfected controls were also examined. The neuronal biomarkers included neurofilament light chain protein (NFL), total and phosphorylated tau (t-tau, p-tau), soluble amyloid precursor proteins alpha and beta (sAPPα, sAPPβ) and amyloid beta (Aβ) fragments 1–42, 1–40 and 1–38. Comparison of the biomarker changes showed a hierarchy of sensitivity in detection and suggested evolving mechanisms with progressive injury. NFL was the most sensitive neuronal biomarker. Its CSF concentration exceeded age-adjusted norms in all HAD patients, 75% of NA CD4<50, 40% of NA CD4 50–199, and 42% of primary infection, indicating common neuronal injury with untreated systemic HIV disease progression as well as transiently during early infection. By contrast, only 75% of HAD subjects had abnormal CSF t-tau levels, and there were no significant differences in t-tau levels among the remaining groups. sAPPα and β were also abnormal (decreased) in HAD, showed less marked change than NFL with CD4 decline in the absence of HAD, and were not decreased in PHI. The CSF Aβ peptides and p-tau concentrations did not differ among the groups, distinguishing the HIV CNS injury profile from Alzheimer's disease. These CSF biomarkers can serve as useful tools in selected research and clinical settings for patient classification, pathogenetic analysis, diagnosis and management.

CSF in Alzheimer's disease

Alzheimer's disease (AD) is a progressive brain amyloidosis that injures brain regions involved in memory consolidation and other cognitive functions. Neuropathologically, the disease is characterized by accumulation of a 42-amino acid protein called amyloid beta, and N-terminally truncated fragments thereof, in extracellular senile plaques together with intraneuronal inclusions of hyperphosphorylated tau protein in neurofibrillary tangles, and neuronal and axonal degeneration and loss. Clinical chemistry tests for these pathologies have been developed for use on cerebrospinal fluid samples. Here, we review what these markers have taught us on the disease process in AD and how they can be implemented in routine clinical chemistry. We also provide an update on new marker development and ongoing analytical standardization effort.

Low levels of HIV-1 RNA detected in the cerebrospinal fluid after up to 10 years of suppressive therapy are associated with local immune activation

OBJECTIVE AND DESIGN

Though combination antiretroviral therapy reduces the concentration of HIV-1 RNA in both plasma and cerebrospinal fluid (CSF) below the detection limit of clinical assays, low levels of HIV-1 RNA are frequently detectable in plasma using more sensitive assays. We examined the frequency and magnitude of persistent low-level HIV-1 RNA in CSF and its relation to the central nervous system (CNS) immune activation.

METHODS

CSF and plasma HIV-1 RNA were measured using the single-copy assay with a detection limit of 0.3 copies/ml in 70 CSF and 68 plasma samples from 45 treated HIV-1-infected patients with less than 40 copies/ml of HIV-1 RNA in both fluids by standard clinical assays. We also measured CSF neopterin to assess intrathecal immune activation. Theoretical drug exposure was estimated using the CNS penetration-efficacy score of treatment regimens.

RESULTS

CSF HIV-1 RNA was detected in 12 of the 70 CSF samples (17%) taken after up to 10 years of suppressive therapy, compared to 39 of the 68 plasma samples (57%) with a median concentration of less than 0.3 copies/ml in CSF compared to 0.3 copies/ml in plasma (P < 0.0001). CSF samples with detectable HIV-1 RNA had higher CSF neopterin levels (mean 8.2 compared to 5.7 nmol/l; P = 0.0085). Patients with detectable HIV-1 RNA in CSF did not differ in pretreatment plasma HIV-1 RNA levels, nadir CD4 cell count or CNS penetration-efficacy score.

CONCLUSION

Low-level CSF HIV-1 RNA and its association with elevated CSF neopterin highlight the potential for the CNS to serve as a viral reservoir and for persistent infection to cause subclinical CNS injury.

Role of HIV in amyloid metabolism

HIV infection has changed from an acute devastating disease to a more chronic illness due to combination anti-retroviral treatment (cART). In the cART era, the life expectancy of HIV-infected (HIV+) individuals has increased. More HIV + individuals are aging with current projections suggesting that 50% of HIV + individuals will be over 50 years old by 2015. With advancing age, HIV + individuals may be at increased risk of developing other potential neurodegenerative disorders [especially Alzheimer's disease (AD)]. Pathology studies have shown that HIV increases intra and possibly extracellular amyloid beta (Aβ42), a hallmark of AD. We review the synthesis and clearance of Aβ42; the effects of HIV on the amyloid pathway; and contrast the impact of AD and HIV on Aβ42 metabolism. Biomarker studies (cerebrospinal fluid AB and amyloid imaging) in HIV + participants have shown mixed results. CSF Aβ42 has been shown to be either normal or diminished in with HIV associated neurocognitive disorders (HAND). Amyloid imaging using [(11)C] PiB has also not demonstrated increased extracellular amyloid fibrillar deposits in HAND. We further demonstrate that Aβ42 deposition is not increased in older HIV + participants using [(11)C] PiB amyloid imaging. Together, these results suggest that HIV and aging each independently affect Aβ42 deposition with no significant interaction present. Older HIV + individuals are probably not at increased risk for developing AD. However, future longitudinal studies of older HIV + individuals using multiple modalities (including the combination of CSF markers and amyloid imaging) are necessary for investigating the effects of HIV on Aβ42 metabolism.

Neurochemical evidence of potential neurotoxicity after prophylactic cranial irradiation

PURPOSE

To examine whether cerebrospinal fluid biomarkers for neuroaxonal damage, neuroglial activation, and amyloid β-related processes could characterize the neurochemical response to cranial radiation.

METHODS AND MATERIALS

Before prophylactic cranial irradiation (PCI) of patients with small cell lung cancer, each patient underwent magnetic resonance imaging of the brain, lumbar puncture, and Mini-Mental State Examination of cognitive function. These examinations were repeated at approximately 3 and 12 months after radiation.

RESULTS

The major findings were as follows. (1) Cerebrospinal fluid markers for neuronal and neuroglial injury were elevated during the subacute phase after PCI. Neurofilament and T-tau increased 120% and 50%, respectively, after PCI (P<.05). The same was seen for the neuroglial markers YKL-40 and glial fibrillary acidic protein, which increased 144% and 106%, respectively, after PCI (P<.05). (2) The levels of secreted amyloid precursor protein-α and -β were reduced 44% and 46%, respectively, 3 months after PCI, and the levels continued to decrease as long as 1 year after treatment (P<.05). (3) Mini-Mental State Examination did not reveal any cognitive decline, indicating that a more sensitive test should be used in future studies.

CONCLUSION

In conclusion, we were able to detect radiation therapy-induced changes in several markers reflecting neuronal injury, inflammatory/astroglial activation, and altered amyloid precursor protein/amyloid β metabolism, despite the low number of patients and quite moderate radiation doses (20-30 Gy). These changes are hypothesis generating and could potentially be used to assess the individual risk of developing long-term symptoms of chronic encephalopathy after PCI. This has to be evaluated in large studies with extended clinical follow-up and more detailed neurocognitive assessments.

Efavirenz promotes β-secretase expression and increased Aβ1-40,42 via oxidative stress and reduced microglial phagocytosis: implications for HIV associated neurocognitive disorders (HAND)

Efavirenz (EFV) is among the most commonly used antiretroviral drugs globally, causes neurological symptoms that interfere with adherence and reduce tolerability, and may have central nervous system (CNS) effects that contribute in part to HIV associated neurocognitive disorders (HAND) in patients on combination antiretroviral therapy (cART). Thus we evaluated a commonly used EFV containing regimen: EFV/zidovudine (AZT)/lamivudine (3TC) in murine N2a cells transfected with the human “Swedish” mutant form of amyloid precursor protein (SweAPP N2a cells) to assess for promotion of amyloid-beta (Aβ) production. Treatment with EFV or the EFV containing regimen generated significantly increased soluble amyloid beta (Aβ), and promoted increased β-secretase-1 (BACE-1) expression while 3TC, AZT, or, vehicle control did not significantly alter these endpoints. Further, EFV or the EFV containing regimen promoted significantly more mitochondrial stress in SweAPP N2a cells as compared to 3TC, AZT, or vehicle control. We next tested the EFV containing regimen in Aβ - producing Tg2576 mice combined or singly using clinically relevant doses. EFV or the EFV containing regimen promoted significantly more BACE-1 expression and soluble Aβ generation while 3TC, AZT, or vehicle control did not. Finally, microglial Aβ phagocytosis was significantly reduced by EFV or the EFV containing regimen but not by AZT, 3TC, or vehicle control alone. These data suggest the majority of Aβ promoting effects of this cART regimen are dependent upon EFV as it promotes both increased production, and decreased clearance of Aβ peptide.

HIV and aging: effects on the central nervous system

With the introduction of combination antiretroviral therapy, many human immunodeficiency virus-positive (HIV+) individuals are reaching advanced age. The proportion of people living with HIV older than 50 years already exceeds 50% in many communities, and is expected to reach this level nationally by 2015. HIV and aging are independently associated with neuropathological changes, but their concurrence may have a more deleterious effect on the central nervous system (CNS). Published data about neurocognitive and neuroimaging markers of HIV and aging are reviewed. Putative factors contributing to neurocognitive impairment and neuroimaging changes in the aging HIV+ brain, such as metabolic disturbances, cardiovascular risk factors, immune senescence, and neuroinflammation, are described. The possible relationship between HIV and some markers of Alzheimer's disease is presented. Current research findings emphasize multiple mechanisms related to HIV and combination antiretroviral therapy that compromise CNS structure and function with advancing age.

Cognitive impairment and major depressive disorder in HIV infection and cerebrospinal fluid biomarkers

Cognitive impairment and major depressive disorder (MDD) are common HIV-1 central nervous system (CNS) complications. Their frequencies in AIDS patients are 36% and 45%, respectively. The diagnoses of HIV cognitive impairment are made by clinical criteria, no single laboratory test or biomarker establishes the diagnosis. Factors of indirect neuronal injury related with the pathophysiology of the HIV infection in the CNS, are the factors studied as biomarkers. In the present no biomarker is established to the diagnosis of HIV cognitive impairment, much still needs to be done. We review in this paper some biomarkers in cerebrospinal fluid that could be valuable to the diagnosis of HIV cognitive impairment. Diagnosing depression in the context of HIV can be challenging, to identify a biomarker that could help in the diagnosis would be very important, although MDD risks and neurobiology are still poorly understood.

Verbal memory declines more rapidly with age in HIV infected versus uninfected adults

OBJECTIVES

In the current era of effective antiretroviral treatment, the number of older adults living with HIV is rapidly increasing. This study investigated the combined influence of age and HIV infection on longitudinal changes in verbal and visuospatial learning and memory.

METHOD

In this longitudinal, case-control design, 54 HIV seropositive and 30 seronegative individuals aged 40-74 years received neurocognitive assessments at baseline visits and again one year later. Assessment included tests of verbal and visuospatial learning and memory. Linear regression was used to predict baseline performance and longitudinal change on each test using HIV serostatus, age, and their interaction as predictors. Multivariate analysis of variance (MANOVA) was used to assess the effects of these predictors on overall baseline performance and overall longitudinal change.

RESULTS

The interaction of HIV and age significantly predicted longitudinal change in verbal memory performance, as did HIV status, indicating that although the seropositive group declined more than the seronegative group overall, the rate of decline depended on age such that greater age was associated with a greater decline in this group. The regression models for visuospatial learning and memory were significant at baseline, but did not predict change over time. HIV status significantly predicted overall baseline performance and overall longitudinal change.

CONCLUSIONS

This is the first longitudinal study focused on the effects of age and HIV on memory. Findings suggest that age and HIV interact to produce larger declines in verbal memory over time. Further research is needed to gain a greater understanding of the effects of HIV on the aging brain.

Brain viral burden, neuroinflammation and neurodegeneration in HAART-treated HIV positive injecting drug users

The long-term impact of chronic human immunodeficiency virus (HIV) infection on brain status in injecting drug users (IDU) treated with highly active antiretroviral therapy (HAART) is unknown. Viral persistence in the brain with ongoing neuroinflammation may predispose to Alzheimer-like neurodegeneration. In this study, we investigated the brains of ten HAART-treated individuals (six IDU and four non-DU), compared with ten HIV negative controls (six IDU and four non-DU). HIV DNA levels in brain tissue were correlated with plasma and lymphoid tissue viral loads, cognitive status, microglial activation and Tau protein and amyloid deposition. Brain HIV proviral DNA levels were low in most cases but higher in HIV encephalitis (n = 2) and correlated significantly with levels in lymphoid tissue (p = 0.0075), but not with those in plasma. HIV positive subjects expressed more Tau protein and amyloid than HIV negative controls (highest in a 58 year old), as did IDU, but brain viral loads showed no relation to Tau and amyloid. Microglial activation linked significantly to HIV positivity (p = 0.001) and opiate abuse accentuated these microglial changes (p = 0.05). This study confirms that HIV DNA persists in brains despite HAART and that opiate abuse adds to the risk of brain damage in HIV positive subjects. Novel findings in this study show that (1) plasma levels are not a good surrogate indicator of brain status, (2) viral burden in brain and lymphoid tissues is related, and (3) while Tau and amyloid deposition is increased in HIV positive IDU, this is not specifically related to increased HIV burden within the brain.

HIV-associated neurocognitive disorder

Neurological involvement in HIV is often associated with cognitive impairment. Although severe and progressive neurocognitive impairment has become rare in HIV clinics in the era of potent antiretroviral therapy, most patients with HIV worldwide have poor outcomes on formal neurocognitive tests. In this Review, we describe the manifestations of HIV-associated neurocognitive disorder in the era of effective HIV therapy, outline diagnosis and treatment recommendations, and explore the research questions that remain. Although comorbid disorders, such as hepatitis C infection or epilepsy, might cause some impairment, their prevalence is insufficient to explain the frequency with which it is encountered. HIV disease markers, such as viral load and CD4 cell counts, are not strongly associated with ongoing impairment on treatment, whereas cardiovascular disease markers and inflammatory markers are. New cerebrospinal fluid and neuroimaging biomarkers are needed to detect and follow impairment. Ongoing research efforts to optimise HIV therapy within the CNS, and potentially to intervene in downstream mechanisms of neurotoxicity, remain important avenues for future investigation. Ultimately, the full control of virus in the brain is a necessary step in the goal of HIV eradication.

Cerebrospinal fluid biomarkers for Alzheimer disease and subcortical axonal damage in 5,542 clinical samples

Introduction

The neuronal loss in Alzheimer disease (AD) has been described to affect grey matter in the cerebral cortex. However, in the elderly, AD pathology is likely to occur together with subcortical axonal degeneration on the basis of cerebrovascular disease. Therefore, we hypothesized that biomarkers for AD and subcortical axonal degeneration would correlate in patients undergoing testing for dementia biomarkers, particularly in older age groups.

Methods

We performed correlation and cluster analyses of cerebrospinal fluid (CSF) biomarker data from 5,542 CSF samples analyzed in our routine clinical neurochemistry laboratory in 2010 through 2012 for the established CSF AD biomarkers total tau (T-tau), phosphorylated-tau (P-tau), amyloid β1-42 (Aβ42), and for neurofilament light (NFL), which is a protein expressed in large-caliber myelinated axons, the CSF levels of which correlate with subcortical axonal injury.

Results

Aβ42, T-tau, and P-tau correlated with NFL. By cluster analysis, we found a bimodal data distribution in which a group with a low Aβ42/P-tau ratio (suggesting AD pathology) had high levels of NFL. High levels of NFL also correlated with the presence of an AD biomarker pattern defined by Aβ42/P-tau and T-tau. Only 29% of those with an AD biomarker signature had normal NFL levels. Age was a possible confounding factor for the associations between NFL and established AD biomarkers, but in a logistic regression analysis, both age and NFL independently predicted the AD biomarker pattern.

Conclusions

The association between an AD-like signature using the established biomarkers Aβ42, T-tau, and P-tau with increased levels of NFL provides in vivo evidence of an association between AD and subcortical axonal degeneration in this uniquely large dataset of CSF samples tested for dementia biomarkers.

Approach to cerebrospinal fluid (CSF) biomarker discovery and evaluation in HIV infection

Central nervous system (CNS) infection is a nearly universal facet of systemic HIV infection that varies in character and neurological consequences. While clinical staging and neuropsychological test performance have been helpful in evaluating patients, cerebrospinal fluid (CSF) biomarkers present a valuable and objective approach to more accurate diagnosis, assessment of treatment effects and understanding of evolving pathobiology. We review some lessons from our recent experience with CSF biomarker studies. We have used two approaches to biomarker analysis: targeted, hypothesis-driven and non-targeted exploratory discovery methods. We illustrate the first with data from a cross-sectional study of defined subject groups across the spectrum of systemic and CNS disease progression and the second with a longitudinal study of the CSF proteome in subjects initiating antiretroviral treatment. Both approaches can be useful and, indeed, complementary. The first is helpful in assessing known or hypothesized biomarkers while the second can identify novel biomarkers and point to broad interactions in pathogenesis. Common to both is the need for well-defined samples and subjects that span a spectrum of biological activity and biomarker concentrations. Previously-defined guide biomarkers of CNS infection, inflammation and neural injury are useful in categorizing samples for analysis and providing critical biological context for biomarker discovery studies. CSF biomarkers represent an underutilized but valuable approach to understanding the interactions of HIV and the CNS and to more objective diagnosis and assessment of disease activity. Both hypothesis-based and discovery methods can be useful in advancing the definition and use of these biomarkers.

CSF Aβ1-42 combined with neuroimaging biomarkers in the early detection, diagnosis and prediction of Alzheimer's disease

The development of validated, qualified, and standardized biomarkers for Alzheimer's disease (AD) that allow for an early presymptomatic diagnosis and discrimination (classification) from other types of dementia and neurodegenerative diseases is warranted to accelerate the successful development of novel disease-modifying therapies. Here, we focus on the value of the 42-residue-long amyloid β isoform (Aβ1-42) peptide in the cerebrospinal fluid as the core, feasible neurobiochemical marker for the amyloidogenic mechanisms in early-onset familial and late-onset sporadic AD. We discuss the role and use of Aβ1-42 in combination with evolving neuroimaging biomarkers in AD detection and diagnosis. Multimodal neuroimaging techniques, directly providing structural-functional-metabolic aspects of brain pathophysiology, are supportive to predict and monitor the progression of the disease. Advances in multimodal neuroimaging provide new insights into brain organization and enable the detection of specific proteins and/or protein aggregates associated with AD. The combination of biomarkers from different methodologies is believed to be of incrementally added risk-value to accurately identify asymptomatic and prodromal individuals who will likely progress to dementia and represent rational biomarker candidates for preventive and symptomatic pharmacological intervention trials.

HIV-1 Nef in macrophage-mediated disease pathogenesis

Combined anti-retroviral therapy (cART) has significantly reduced the number of AIDS-associated illnesses and changed the course of HIV-1 disease in developed countries. Despite the ability of cART to maintain high CD4+ T-cell counts, a number of macrophage-mediated diseases can still occur in HIV-infected subjects. These diseases include lymphoma, metabolic diseases, and HIV-associated neurological disorders. Within macrophages, the HIV-1 regulatory protein "Nef" can modulate surface receptors, interact with signaling pathways, and promote specific environments that contribute to each of these pathologies. Moreover, genetic variation in Nef may also guide the macrophage response. Herein, we review findings relating to the Nef-macrophage interaction and how this relationship contributes to disease pathogenesis.

HIV-associated neurocognitive disease: case studies and suggestions for diagnosis and management in different patient subgroups

The incidence of HIV-associated dementia has decreased significantly with the introduction of combination antiretroviral therapy; however, milder or more subtle forms of neurocognitive disorders associated with HIV appear to remain common. There is a lack of consensus on when to screen and on which methods are most appropriate for identifying patients at risk of neurocognitive impairment. Multiple factors (demographic, social, genetic, psychological and medical) can play a role in its aetiology and progression, including potential central nervous system toxicity of antiviral therapy. It is important to identify these factors in order to apply relevant management strategies. In this review, we discuss a series of case studies that address some of the challenges presented by the diagnosis and management of HIV-associated neurocognitive impairment in different patient types.

Cerebrospinal fluid and neuroimaging biomarker abnormalities suggest early neurological injury in a subset of individuals during primary HIV infection

BACKGROUND

Cerebrospinal fluid (CSF) and neuroimaging abnormalities demonstrate neuronal injury during chronic AIDS, but data on these biomarkers during primary human immunodeficiency virus (HIV) infection is limited.

METHODS

We compared CSF concentrations of neurofilament light chain, t-tau, p-tau, amyloid precursor proteins, and amyloid-beta 42 in 92 subjects with primary HIV infection and 25 controls. We examined relationships with disease progression and neuroinflammation, neuropsychological testing, and proton-magnetic resonance spectroscopy (MRS)-based metabolites.

RESULTS

Neurofilament light chain was elevated in primary HIV infection compared with controls (P = .0004) and correlated with CSF neopterin (r = 0.38; P = .0005), interferon gamma-induced protein 10 (r = 0.39; P = .002), white blood cells (r = 0.32; P = .004), protein (r = 0.59; P < .0001), and CSF/plasma albumin ratio (r = 0.60; P < .0001). Neurofilament light chain correlated with decreased N-acteylaspartate/creatine and glutamate/creatine in the anterior cingulate (r = -0.35, P = .02; r = -0.40, P = .009, respectively), frontal white matter (r = -0.43, P = .003; r = -0.30, P = .048, respectively), and parietal gray matter (r = -0.43, P = .003; r = -0.47, P = .001, respectively). Beta-amyloid was elevated in the primary infection group (P = .0005) and correlated with time infected (r = 0.34; P = .003). Neither marker correlated with neuropsychological abnormalities. T-tau and soluble amyloid precursor proteins did not differ between groups.

CONCLUSIONS

Elevated neurofilament light chain and its correlation with MRS-based metabolites suggest early neuronal injury in a subset of participants with primary HIV infection through mechanisms involving central nervous system inflammation.

Cerebral β-amyloid deposition predicts HIV-associated neurocognitive disorders in APOE ε4 carriers

OBJECTIVE

The apolipoprotein E (APOE) ε4 allele enhances cerebral accumulation of β-amyloid (Aβ) and is a major risk factor for sporadic Alzheimer's disease. We hypothesized that HIV-associated neurocognitive disorders (HAND) would be associated with the APOE ε4 genotype and cerebral Aβ deposition.

DESIGN

Clinicopathological study of HIV-infected adults from four prospective cohorts in the US National NeuroAIDS Tissue Consortium.

METHODS

We used multivariable logistic regressions to model outcomes [Aβ plaques (immunohistochemistry) and HAND (standard criteria)] on predictors [APOE ε4 (allelic discrimination assay), older age (≥50 years), Aβ plaques, and their two-way interactions] and comorbid factors.

RESULTS

Isocortical Aβ deposits generally occurred as diffuse plaques and mild-to-moderate amyloid angiopathy. Isocortical phospho-Tau-immunoreactive neurofibrillary lesions were sparse. The APOE ε4 and older age were independently associated with the presence of Aβ plaques [adjusted odds ratio (OR) 10.16 and 5.77, 95% confidence interval (CI) 2.89 - 35.76 and 1.91-17.48, P = 0.0003 and 0.0019, respectively, n = 96]. The probability of HAND was increased in the presence of Aβ plaques among APOE ε4 carriers (adjusted OR 30.00, 95% CI 1.41-638.63, P = 0.029, n = 15), but not in non-ε4 carriers (n = 57).

CONCLUSION

The APOE ε4 and older age increased the likelihood of cerebral Aβ plaque deposition in HIV-infected adults. Generally, Aβ plaques in HIV brains were immunohistologically different from those in symptomatic Alzheimer's disease brains. Nonetheless, Aβ plaques were associated with HAND among APOE ε4 carriers. The detection of APOE ε4 genotype and cerebral Aβ deposition biomarkers may be useful in identifying living HAND patients who could benefit from Aβ-targeted therapies.

Cognitive impairment in HIV infection is associated with MRI and CSF pattern of neurodegeneration

BACKGROUND AND PURPOSE

Biomarkers as indicators for the progression of human immunodeficiency virus (HIV)-associated neurocognitive disorders (HAND) remain still elusive. We performed a cross-sectional study to analyze the correlation between cognitive impairment, abnormalities in magnetic resonance imaging (MRI), and cerebrospinal fluid (CSF) markers of neurodegeneration in HIV-infected patients.

METHODS

We enrolled 94 patients (82 men and 12 women; mean age 45 ± 10 years) with HIV infection, but without opportunistic infections of the CNS. All patients underwent MRI and CSF analysis. The global pattern of white matter signal intensity abnormalities, the index of atrophy, the severity of periventricular white matter abnormalities, and the severity of basal ganglia signal changes were analyzed. We measured CSF markers of neurodegeneration (total tau, phospho-tau, beta-amyloid). The findings of this evaluation were correlated with demographic and infection parameters of the patients in blood and CSF.

RESULTS

We found a highly significant correlation between the severity of global brain atrophy, basal ganglia signal changes, and cognitive impairment in HIV-infected patients. Furthermore, cognitive impairment was significantly correlated with total tau, but not with phospho-tau or A-beta-amyloid in CSF analysis.

CONCLUSIONS

Our results confirm the significant correlation between MRI changes and cognitive impairment in HIV infection. Furthermore, we could show that global brain atrophy and signal changes in basal ganglia are the typical MRI pattern in HAND. The correlation between cognitive impairment and total tau, but not phospho-tau, supports the hypothesis that HAND are not a subtype of Alzheimer's dementia.