On cerebrospinal fluid biomarkers of HIV-1 infection

HIV invades the central nervous system (CNS) shortly after transmission and is present throughout the course of infection, causing immune activation and neuroinflammation. If left untreated, more than 20% of patients with late-stage HIV/AIDS develop HIV-associated dementia (HAD). With combined antiretroviral treatment (cART), HAD is rare, but mild neurocognitive deficits are commonly noted and have been termed HIV-associated neurocognitive disorders (HAND). The diagnosis of HAND relies solely on neuropsychological testing, which might overestimate the prevalence of HAND. Analysis of biomarkers could enhance diagnostic precision. With an aging HIV-infected population, methods to distinguish HAND from other dementias, especially Alzheimer’s disease (AD), will increase in importance. This thesis evaluates biomarkers related to neuronal injury (neurofilament light chain protein [NFL] and total tau [t-tau]); immune activation (neopterin); and altered metabolism (soluble amyloid precursor protein α and β [sAPP], beta-amyloid1-42 [Aβ1-42], and phosphorylated tau [p-tau]) in cerebrospinal fluid (CSF) of HIV patients with and without cognitive deficits. For the purposes of differential diagnosis, AD patients and HIV-negative subjects with CNS infections were included. HAD patients exhibited a biomarker pattern with normal to low Aβ1-42, decreased sAPPs, normal p-tau, and increased t-tau, thus differentiating HAD from AD, neuroasymptomatic (NA) HIV-infected patients, and controls. Although CSF p-tau occurs physiologically with aging, p-tau levels were normal or decreased in HIV. HIV-related opportunistic infections (OI) and CNS infections in HIV-negatives were similar to HAD, indicating that neuroinflammation might induce a pathologic processing of amyloid that is separate from the metabolism in AD. Amyloid and tau metabolites could be useful biomarkers to distinguish HAD from AD. CSF NFL was highest in HAD patients, but NA patients, both with and without cART, also exhibited increases in NFL. This indicates ongoing axonal disruption at all stages of HIV, including some patients on cART. Most likely this is due to HIV-induced axonal disruption. CSF NFL levels increased in younger HIV-infected patients as compared to controls

Cerebrospinal fluid Alzheimer's biomarker profiles in CNS infections.

The cerebrospinal fluid (CSF) biomarker profile in Alzheimer's disease (AD) is characterized by decreased beta amyloid (Aβ(1-42)), increased total and hyperphosphorylated tau (t-tau and p-tau, respectively), which is a useful diagnostic tool and gives insight in the pathogenesis of AD. It is of importance to study how these biomarkers react in other CNS diseases; therefore, we decided to analyse amyloid and tau biomarkers in different CNS infections. We also included analysis of soluble amyloid precursor proteins (sAPPα and -β). CSF Aβ(1-42), sAPPα and -β, t-tau and p-tau were analysed in bacterial meningitis (n = 12), Lyme neuroborreliosis (n = 13), herpes simplex virus type 1 (HSV-1) encephalitis (n = 10), HIV-associated dementia (HAD) (n = 21), AD (n = 21) and healthy controls (n = 42). Concurrent with AD, Aβ(1-42) was decreased in all groups except neuroborreliosis compared to controls. HSV-1 encephalitis, bacterial meningitis and HAD showed lower concentrations of sAPPα and -β compared to AD. T-tau was increased in AD and HSV-1 encephalitis compared to all other groups. P-tau was higher in AD and HSV-1 encephalitis compared to bacterial meningitis, HAD and control. Decreased CSF Aβ(1-42), sAPPα and -β in various CNS infections imply an effect of neuroinflammation on amyloid metabolism which is similar in regard to AD concerning Aβ(1-42), but differs concerning sAPPα and -β. These results clearly indicate different pathologic pathways in AD and infectious CNS disease and may provide help in the differential biomarker diagnostics. Increased p-tau in HSV-1 encephalitis probably reflect acute neuronal damage and necrosis

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

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

Biomarker Evidence of Axonal Injury in Neuroasymptomatic HIV-1 Patients

Prevalence of neurocognitive impairment in HIV-1 infected patients is reported to be high. Whether this is a result of active HIV-related neurodegeneration is unclear. We examined axonal injury in HIV-1 patients by measuring the light subunit of neurofilament protein (NFL) in CSF with a novel, sensitive method.With a cross-sectional design, CSF concentrations of neurofilament protein light (NFL) (marker of neuronal injury), neopterin (intrathecal immunoactivation) and CSF/Plasma albumin ratio (blood-brain barrier integrity) were analyzed on CSF from 252 HIV-infected patients, subdivided into untreated neuroasymptomatics (n = 200), HIV-associated dementia (HAD) (n = 14) and on combinations antiretroviral treatment (cART) (n = 85), and healthy controls (n = 204). 46 HIV-infected patients were included in both treated and untreated groups, but sampled at different timepoints. Furthermore, 78 neuroasymptomatic patients were analyzed before and after treatment initiation. While HAD patients had the highest NFL concentrations, elevated CSF NFL was also found in 33% of untreated neuroasymptomatic patients, mainly in those with blood CD4+ cell counts below 250 cells/μL. CSF NFL concentrations in the untreated neuroasymptomatics and treated groups were equivalent to controls 18.5 and 3.9 years older, respectively. Neopterin correlated with NFL levels in untreated groups while the albumin ratio correlated with NFL in both untreated and treated groups. Increased CSF NFL indicates ongoing axonal injury in many neuroasymptomatic patients. Treatment decreases NFL, but treated patients retain higher levels than controls, indicating either continued virus-related injury or an aging-like effect of HIV infection. NFL correlates with neopterin and albumin ratio, suggesting an association between axonal injury, neuroinflammation and blood-brain barrier permeability. NFL appears to be a sensitive biomarker of subclinical and clinical brain injury in HIV and warrants further assessment for broader clinical use

Univariate correlation (left columns) and multiple linear regression (right columns) determining predictors of log₁₀ CSF NFL in HIV-infected neuroasymptomatic patients with and without antiretroviral treatment.

<p>*CD4+ T-cell count was inverse transformed (1/(CD4+45·3) NS = Not significant.</p

CSF NFL related to age and treatment effect.

<p>Since CSF NFL increases with age, we analyzed the group differences with a linear mixed effects model with age as covariate. This implies a model with three parallel regression lines where the group differences correspond to the vertical distances between the regression lines. The group differences can be expressed as the corresponding age increase needed for an equivalent difference. The 95% prediction interval of CSF NFL levels of HIV-negative controls is demonstrated as dotted lines (Neg 95% PI). Concentrations of CSF NFL in neuroasymptomatic untreated HIV-infected subjects (No ART) were equivalent to those of HIV-negative subjects (negative) who were 18.5 years older (p<0.001). CSF NFL concentrations in the treated group (ART) were equivalent to those of HIV-negative subjects who were 3.9 years older (p<0.01).</p

Cross-sectional analysis of CSF NFL in HIV disease.

<p>Included were 14 subjects diagnosed with HIV-associated dementia (HAD); HIV positive neuroasymptomatic subjects (NA) without antiretroviral treatment stratified according to levels of blood CD4 T-cells <50 (n = 42), 50–199 (n = 49), 200–349 (n = 52) and >350 (n = 57); 85 subjects on combination antiretroviral treatment (ART) for at least one year and plasma HIV-RNA <50 copies/ml and 204 HIV seronegative volunteers (HIV-neg). CSF NFL concentrations were higher in patients with HAD compared to all other groups. Elevated levels of CSF NFL was also found in subjects with a CD4+ T-cell count below 50 cells/mL compared to groups in higher CD4+ T-cell count strata. Whiskers represent full range</p

CSF NFL levels before-after combination antiretroviral treatment (cART) initiation.

<p>Overall CSF NFL levels decreased in 63% of the patients after initiation of cART (p<0.01), demonstrated as a lower CSF NFL geometric mean (dotted line) after initiation of cART. 33% of the patents had elevated levels of CSF NFL at baseline and 81% of those exhibited reduction in their CSF NFL levels after treatment (p<0.01). 35% of patients with pathological CSF NFL at baseline normalized their levels (green colored). Those with normal CSF NFL at baseline exhibited no significant reduction in CSF NFL (blue colored). Three patients with normal baseline CSF NFL exhibited elevated levels of CSF NFL after cART initiation (red colored).</p