Biokinetic analysis of ubiquitin C-terminal hydrolase-L1 (UCH-L1) in severe traumatic brain injury patient biofluids

Abstract

Ubiquitin C-terminal hydrolase-L1 (UCH-L1) is a neuron-specific enzyme that has been identified as a potential biomarker of traumatic brain injury (TBI). The study objectives were to determine UCH-L1 exposure and kinetic metrics, determine correlations between biofluids, and assess outcome correlations in severe TBI patients. Data were analyzed from a prospective, multicenter study of severe TBI (Glasgow Coma Scale [GCS] score ≤ 8). Cerebrospinal fluid (CSF) and serum data from samples taken every 6 h after injury were analyzed by enzyme-linked immunosorbent assay (ELISA). UCH-L1 CSF and serum data from 59 patients were used to determine biofluid correlations. Serum samples from 86 patients and CSF from 59 patients were used to determine outcome correlations. Exposure and kinetic metrics were evaluated acutely and up to 7 days post-injury and compared to mortality at 3 months. There were significant correlations between UCH-L1 CSF and serum median concentrations (r(s)=0.59, p<0.001), AUC (r(s)=0.3, p=0.027), Tmax (r(s)=0.68, p<0.001), and MRT (r(s)=0.65, p<0.001). Outcome analysis showed significant increases in median serum AUC (2016 versus 265 ng/mL*min, p=0.006), and Cmax (2 versus 0.4 ng/mL, p=0.003), and a shorter Tmax (8 versus 19 h, p=0.04) in those who died versus those who survived, respectively. In the first 24 h after injury, there was a statistically significant acute increase in CSF and serum median Cmax((0-24h)) in those who died. This study shows a significant correlation between UCH-L1 CSF and serum median concentrations and biokinetics in severe TBI patients, and relationships with clinical outcome were detected.

FIG. 1.

Ubiquitin C-terminal hydrolase-L1 (UCH-L1) brain specificity and antibody-based immunoblotting detection of UCH-L1 following severe traumatic brain injury (TBI). (A) UCH-L1 shows strong brain enrichment and specificity among various human tissues. (B) UCH-L1 was also detected and elevated in cerebrospinal fluid (CSF; 6 and 24 h) from two randomly-selected TBI patients (TBI-1 and TBI-2) in comparison to three separate CSF controls (Con) by immunoblotting. Polyclonal antibody was used, but monoclonal antibody also produced similar results.

FIG. 2.

Temporal profiles for cerebrospinal fluid (CSF) and serum ubiquitin C-terminal hydrolase-L1 (UCH-L1) median concentrations at standardized 6-h time points up to 7 days post-injury (r_s=0.59, p<0.001). Control median concentrations are shown for comparison. Data were not available for all patients at all time points, and the sample size for each time point is listed in the grid below the graph. Correlations between CSF and serum were performed using Spearman's rank correlation. The line in the box indicates the median value of the data, the upper edge of the box indicates the 75th percentile of the data set, and the lower edge indicates the 25th percentile. The ends of the vertical lines indicate the minimum and maximum data values.

FIG. 3.

Median ubiquitin C-terminal hydrolase-L1 (UCH-L1) area under the curve (AUC) for cerebrospinal fluid (CSF) and serum dichotomized by time in traumatic brain injury (TBI) patients. AUC 24 hours describes the area under the curve for 0–24 hours after injury. Total AUC represents the total area under the curve over the 7-day study period. The AUC 24 hours was 34% of the total AUC for CSF and 61% of the total AUC for serum. AUC is expressed in ng/mL*h. The line in the box indicates the median value of the data, the upper edge of the box indicates the 75th percentile of the data set, and the lower edge indicates the 25th percentile. The ends of the vertical lines indicate the minimum and maximum data values.

FIG. 4.

Median cerebrospinal fluid (CSF) and serum ubiquitin C-terminal hydrolase-L1 (UCH-L1) standardized 6-h time points for the 7-day study period for those that survived (CSF n=28; serum n=30), versus non-survivors (CSF n=16; serum n=24), at 3 months post-injury. These differences over time resulted in statistically significant differences in serum UCH-L1 biokinetics in those who had poor outcomes. Data were not available for all patients at all time points. The line in the box indicates the median value of the data, the upper edge of the box indicates the 75th percentile of the data set, and the lower edge indicates the 25th percentile. The ends of the vertical lines indicate the minimum and maximum data values.