Assessing Blood-Brain Barrier Integrity and Neuroinflammation in HIV

Albumin levels were measured in serum and CSF through Immunoturbidimetric methods (AU 5800, Beckman Coulter, Brea, CA, USA). CSAR, intended as a ratio between CSF albumin (mg/L)/serum albumin (g/L), was employed to evaluate BBB function: the definition of BBB damage was derived from age-adjusted Reibergrams (normal if below 6.5 in patients with age <40 years and below 8 in patients with >40 years) [8 (link)]. Following CNS inflammation, biomarkers were evaluated: CSF total tau (t-tau, a microtubule-associated protein predominantly expressed in the neurons and associated with taupathologies, such as Alzheimer disease), phosphorylated tau (p-tau, the phosphorilated form which leads to stabilize microtubule assembly), and β- amyloid1-42 (Aβ1-42, produced from amyloid-β precursor protein and accumulated in Alzheimer disease) were quantified by immunoenzymatic methods (Innogenetics) with limits of detection of 87, 15, and 87 pg/mL, respectively. Neopterin, a marker of cellular immune system activation and CNS inflammation, was determined through validated ELISA methods (DRG Diagnostics). Reference values were as follows: t-tau [<300 pg/mL (in patients aged 21–50), <450 pg/mL (in patients aged 51–70), or <500 pg/mL in older patients], p-tau (<61 pg/mL), 1–42 beta amyloid (>500 pg/mL), and neopterin (<1.5 ng/mL).
Circulating HIV RNA was quantified by a real-time polymerase chain reaction (PCR) assay CAP/CTM HIV-1 vs. 2.0 (CAP/CTM, Roche Molecular System, Branchburg, NJ, USA; detection limit: 20 copies/mL of HIV-1 RNA). CSF escape was defined as CSF HIV RNA above 50 copies/mL in patients with plasma HIV RNA below 50 copies/mL or as CSF HIV RNA 1 log₁₀ higher than plasma HIV RNA in patients with a detectable plasma viral load. HAND was diagnosed according to the Frascati criteria.