Clinical utility of serum levels of ubiquitin C-terminal hydrolase as a biomarker for severe traumatic brain injury

Abstract

Background: Brain damage markers released in cerebrospinal fluid (CSF) and blood may provide valuable information about diagnosis and outcome prediction after traumatic brain injury (TBI).

Objective: To examine the concentrations of ubiquitin C-terminal hydrolase-L1 (UCH-L1), a novel brain injury biomarker, in CSF and serum of severe TBI patients and their association with clinical characteristics and outcome.

Methods: This case-control study enrolled 95 severe TBI subjects (Glasgow Coma Scale [GCS] score, 8). Using sensitive UCH-L1 sandwich ELISA, we studied the temporal profile of CSF and serum UCH-L1 levels over 7 days for severe TBI patients.

Results: Comparison of serum and CSF levels of UCH-L1 in TBI patients and control subjects shows a robust and significant elevation of UCH-L1 in the acute phase and over the 7-day study period. Serum and CSF UCH-L1 receiver-operating characteristic curves further confirm strong specificity and selectivity for diagnosing severe TBI vs controls, with area under the curve values in serum and CSF statistically significant at all time points up to 24 hours (P < .001). The first 12-hour levels of both serum and CSF UCH-L1 in patients with GCS score of 3 to 5 were also significantly higher than those with GCS score of 6 to 8. Furthermore, UCH-L1 levels in CSF and serum appear to distinguish severe TBI survivors from nonsurvivors within the study, with nonsurvivors having significantly higher and more persistent levels of serum and CSF UCH-L1. Cumulative serum UCH-L1 levels > 5.22 ng/mL predicted death (odds ratio, 4.8).

Conclusion: Serum levels of UCH-L1 appear to have potential clinical utility in diagnosing TBI, including correlating to injury severity and survival outcome.

Fig. 1. Characterization of UCH-L1 antigen calibrator, capture and detection antibodies and sandwich ELISA performance

(A) Recombinant His-tag human UCH-L1 (20 μg) from E. coli was analyzed by SDS-electrophoresis gel stained with Coomassie blue to show proper molecular wright and purity. (B) Capture (Mouse IgM 2018) and detection (Rabbit IgG #21687) antibodies were charactrerized by their specific recognition of recombinant human UCH-L1 (100 ng; see above) and native human UCH-L1 target in human brain vs. other organ lysates (20 μg). (C) Optimized sandwich ELISA was subjected to performance analysis in both CSF and serum matrix. Shown were averages of accumulative data from 17 multi-day standard curve analysis. Background (no antigen) chemiluiminescent values + 3 x SD were also shown on Y-axis and as horizontal line. The horizontal line represents the average background chemiluminescence (no antigen) + 3 x standard deviation = 2,000 chemiluminescence units. MWM = molecular weight marker lane.

Fig. 2. Temporal profile of CSF and serum UCH-L1 levels over 7 days for severe TBI patients in comparison to control subjects

Data shown are measured by ELISA. Mean ± SEM concentrations are shown. For Control subjects – only single time point samples used.

Fig. 3. UCH-L1 Receiver Operation Characteristics (ROC) Curves

Comparing 24 h post injury TBI CSF (A) and serum (C) UCH-L1 level vs. CSF controls or serum normal controls, respectively. Area under the curve (AUC) over time was also plotted (B, D).

Fig. 4. Comparison UCH-L1 levels in CSF (A) and in Serum (B) in survivors versus non-survivors

(over study duration and 6 hrs post-injury). *p= 0.05; Mann-Whitney U test).

Fig. 5. Comparison of CSF (A) and Serum (B) levels of UCH-L1 in patients with TBI who survived versus non-survivors within 7 days from TBI

The graphs show time course of serum and CSF UCH-L1 levels in patients who survived or died. There was a marked difference between the two outcome groups. Increased initial levels of UCH-L1 and secondary increases indicate severe primary injury and the possibility of secondary brain damage associated with death.