Parallel CSF and serum temporal profile assessment of axonal injury biomarkers NF-L and pNF-H: Associations with patient outcome in moderate-severe traumatic brain injury.

Neurofilament-light chain (NF-L) and phosphorylated neurofilament-heavy chain (pNF-H) are axonal proteins that have been reported as potential diagnostic and prognostic biomarkers in traumatic brain injury (TBI). However, detailed temporal profiles for these proteins in blood, and interrelationships in the acute and chronic time periods post-TBI have not been established. Our objectives were 1) to characterize acute-to-chronic serum NF-L and pNF-H profiles after moderate-severe TBI, as well as acute cerebrospinal fluid (CSF) levels, 2) to evaluate CSF and serum NF-L and pNF-H associations with each other, and 3) to assess biomarker associations with global patient outcome using both the Glasgow Outcome Scale-Extended (GOS-E) and Disability Rating Scale (DRS). In this multi-cohort study, we measured serum and CSF NF-L and pNF-H levels in samples collected from two clinical cohorts (University of Pittsburgh [UPITT] and Baylor College of Medicine [BCM]) of individuals with moderate-to-severe TBI. The UPITT cohort includes 279 subjects from an observational cohort study; we obtained serum (n=277 unique subjects) and CSF (n=95 unique subjects) daily for one week, and serum every two weeks for six months. The BCM cohort included 103 subjects from a previous randomized clinical trial of erythropoietin and blood transfusion threshold after severe TBI, which showed no effect on neurological outcome between treatment arms; serum (n=99 unique subjects) and CSF (n=54 unique subjects) NF-L and pNF-H levels were measured at least daily during days (D) 0-10 post-injury. GOS-E and DRS were assessed at 6 months (both cohorts) and 12 months (UPITT cohort only). Results show serum NF-L and pNF-H gradually rise during the first 10 days and peak at D20-30 post-injury. In the UPITT cohort, acute (D0-6) NF-L and pNF-H levels correlate within CSF and serum (Spearman r=0.44-0.48; p<0.05). In the UPITT cohort, acute NF-L CSF and serum levels, as well as chronic (M2-6) serum NF-L levels, were higher among individuals with unfavorable GOS-E and worse DRS at 12 months (p<0.05, all comparisons). In the BCM cohort, higher acute serum NF-L levels were also associated with unfavorable GOS-E. Higher pNF-H serum concentrations (D0-6 and M2-6), but not CSF pNF-H, were associated with unfavorable GOS-E and worse DRS (p<0.05, all comparisons) in the UPITT cohort. Relationships between biomarker levels and favorable outcome persisted after controlling for age, sex, and GCS. This study shows for the first time that serum levels of NF-L and pNF-H peak at D20-30 post-TBI. Serum NF-L levels, and to a lesser extent pNF-H levels, are robustly associated with global patient outcomes and disability after moderate-to-severe TBI. Further studies on clinical utility as prognosis and treatment-response indicators are needed.