Emerging themes from the literature on circulating biomarkers of traumatic brain injury

Effect of blood alcohol on the diagnostic accuracy of glial fibrillary acidic protein and ubiquitin carboxy-terminal hydrolase L1 for traumatic intracranial hemorrhage: A TRACK-TBI study

BACKGROUND

Acute intoxication is common in patients evaluated for traumatic brain injury (TBI). However, the effect of elevated blood alcohol levels (BALs) on the diagnostic accuracy of FDA-cleared biomarkers for evaluating traumatic intracranial injury on computed tomography (CT) scan, namely, glial fibrillary acidic protein (GFAP) and ubiquitin carboxy-terminal hydrolase L1 (UCH-L1), has not been well studied.

METHODS

We investigated the effect of significantly elevated (>300 mg/dL) and modestly elevated BAL (81-300 mg/dL) at emergency department presentation on the diagnostic accuracy of GFAP and UCH-L1 for predicting a positive CT in patients presenting to 18 U.S. Level I trauma centers within 24 h of TBI as part of the prospective, Transforming Research and Clinical Knowledge in TBI (TRACK-TBI) study. Plasma GFAP and UCH-L1 were measured using Abbott i-STAT Alinity and ARCHITECT assays. Discrimination was evaluated using the area under the receiver operating characteristic curve (AUC).

RESULTS

Of 2320 TRACK-TBI participants studied, 54 (2.3%), 332 (14.3%), 1209 (52.1%), and 725 (31.3%) had significantly elevated BAL, modestly elevated BAL, nonelevated BAL (0-80 mg/dL), and no BAL available, respectively; 48.3% of the cohort had a positive brain CT. Those with significantly elevated and modestly elevated BAL were more likely to have positive CT (61.1% and 60.5% vs. 46.9% and 44.0%) and had higher plasma GFAP and UCH-L1 levels than those with nonelevated BAL and no BAL available. The AUC of GFAP and UCH-L1 combined for predicting CT positivity was higher in those with significantly elevated BAL (0.949) than those with modestly elevated BAL (0.858), nonelevated BAL (0.849), and no BAL available (0.883).

CONCLUSIONS

Modestly and significantly elevated BAL does not lower the diagnostic accuracy of GFAP and UCH-L1 for predicting traumatic intracranial injury on CT. These biomarkers may be useful in decreasing avoidable brain CT imaging in persons with acute alcohol intoxication.

Performance Evaluation of a Multiplex Assay for Simultaneous Detection of Four Clinically Relevant Traumatic Brain Injury Biomarkers

Traumatic brain injury (TBI) results in heterogeneous pathology affecting multiple cells and tissue types in the brain. It is likely that assessment of such complexity will require simultaneous measurement of multiple molecular biomarkers in a single sample of biological fluid. We measured glial fibrillary acidic protein (GFAP), ubiquitin c-terminal hydrolase L1 (UCH-L1), neurofilament light chain (NF-L) and total tau in plasma samples obtained from 107 subjects enrolled in the Transforming Research and Clinical Knowledge in Traumatic Brain Injury Pilot (TRACK-TBI Pilot) Study using the Quanterix Simoa 4-Plex assay. We also measured NF-L using the Simoa singleplex assay. We computed the correlation between the different biomarkers and calculated the discriminative value of each biomarker for distinguishing between subjects with abnormal versus normal head computed tomography (CT). We found a strong correlation between NF-L values derived from the multiplex and singleplex assays (correlation coefficient = 0.997). Among biomarker values derived from the multiplex assay, the strongest correlation was between the axonal and neuronal markers, NF-L and UCH-L1 (coefficient = 0.71). The weakest correlation was between the glial marker GFAP and the axonal marker tau (coefficient = 0.06). The areas under the curves for distinguishing between subjects with/without abnormal head CT for multiplex GFAP, UCH-L1, NF-L, and total tau were: 0.88 (95% confidence interval 0.81-0.95), 0.86 (0.79-0.93), 0.84 (0.77-0.92), and 0.77 0.67-0.86), respectively. We conclude that the multiplex assay provides simultaneous quantification of GFAP, UCH-L1, NF-L, and tau, and may be clinically useful in the diagnosis of TBI as well as identifying different types of cellular injury.

Valproic Acid Treatment Decreases Serum Glial Fibrillary Acidic Protein and Neurofilament Light Chain Levels in Swine Subjected to Traumatic Brain Injury

The primary aim of this study was to examine the effects of valproic acid (VPA) treatment on serum glial fibrillary acidic protein (GFAP) and neurofilament light chain (NF-L) levels. To achieve this aim, we obtained serum samples from: 1) 10 Yorkshire swine subjected to controlled cortical impact traumatic brain injury (CCI TBI) + polytrauma and randomized to receive either normal saline (NS) + VPA (n = 5) or NS alone (n = 5) and 2) five additional swine subjected to CCI TBI without polytrauma and treated with VPA. GFAP and NF-L levels were measured in samples obtained from baseline until 10 days post-injury using a digital immunoassay from Quanterix Corporation. We found that elevated GFAP and NF-L levels were first detected at 2 h post-injury; and peaked at 24 h and 72 h respectively. GFAP levels returned to baseline levels by Day 10, while NF-L remained elevated at Day 10. In TBI + polytrauma swine, the magnitude and duration of biomarker elevation, quantified by the area under the biomarker-concentration-versus-time curve during the first 10 days (AUC_0-10days), was higher in the NS group, compared with the VPA group. For GFAP, the AUC_0-10days was 45,535 (IQR: 35,741-105,711) and 22,837 (IQR: 8,082-46,627) for the NS and NS+VPA groups, respectively. For NF-L, the AUC_0-10days was 43,073 (IQR: 18,739-120,794) and 4,475 (2,868-11,157) for the NS and NS+VPA groups, respectively. Twenty-four hour GFAP and NF-L levels had the strongest correlation with lesion size and time to normalization of behavior. Accordingly, we conclude that treatment with VPA results in significantly lower serum GFAP and NF-L levels. The time-point at which GFAP and NF-L levels have the strongest correlation with outcome is 24 h post-injury.