Evaluation of UCH-L1 and T-Tau as prognostic biomarkers of traumatic brain injury

Abstract

AimThe current study aimed to evaluate the ability of ubiquitin C-terminal hydrolase L1 (UCH-L1) and total Tau (T-Tau) to predict the need for neurosurgical intervention and neurological outcome in patients with acute mild to moderate traumatic brain injury (TBI).MethodsEighty-five patients diagnosed with acute mild to moderate TBI were included in this study. Serum levels of UCH-L1 and T-Tau were measured using enzyme-linked immunosorbent assay (ELISA) technique. Outcome measures were the need for surgical intervention and Glasgow Outcome Scale (GOS), which was evaluated 3 months after the initial trauma. The outcomes were dichotomized into good outcomes (GOS=5) and poor outcomes (GOS<5).ResultsSerum levels of both UCH-L1 and T-Tau were significantly elevated in TBI patients who required neurosurgical intervention and those who had a poor outcome. Receiver operating characteristic (ROC) analysis revealed that UCH-L1 could predict the need for neurosurgical intervention and poor outcome with an accuracy of 82.4% (AUC= 0.872) and 83.5% (AUC= 0.878), respectively. Regarding T-Tau, it could predict the need for surgical intervention and poor outcome with an accuracy of 89.4% (AUC= 0.909) and 90.6% (AUC= 0.916), respectively.ConclusionBoth UCH-L1 and T-Tau can be used for outcome prediction in cases of mild to moderate TBI. However, t-tau could be a better prognostic biomarker of TBI as it was more accurate than UCH-L1.

Keywords

Introduction

Traumatic brain injury (TBI) is defined as a disruption in normal brain function caused by sudden trauma to the head. The annual incidence of TBI is estimated at 50 million cases worldwide.¹ Mild TBI accounts for 85% of all cases. Although most patients recover completely, predicting long-term complications remains difficult for clinicians.²
The pathophysiology of TBI is not fully understood. It is suggested that TBI results from primary impact and secondary effects including neuronal inflammation, blood–brain barrier disruption, and metabolic disturbances. These secondary effects are considered risk factors for persistent symptoms and poor outcomes.³
In the Emergency Department (ED), the main diagnostic and prognostic tools are the Glasgow Coma Scale (GCS) and head computed tomography (CT). However, GCS is subjective, and CT has limited sensitivity to diffuse injuries such as traumatic axonal injury.⁴
Surgical intervention is one of the main treatment options for TBI. It is most effective for large intracranial hematomas and is required in cases of brain edema and increased intracranial pressure refractory to medical treatment.⁵
A biomarker is an objective indicator of a patient’s biological state that can be measured precisely and consistently.⁶ Several biomarkers such as S100 calcium-binding protein B (S100B), glial fibrillary acidic protein (GFAP), and neuron-specific enolase (NSE) have been studied in TBI, but results remain controversial.^7-8 Ubiquitin C-terminal hydrolase-L1 (UCH-L1) is a low molecular weight stable protein involved in axonal transport and removal of misfolded proteins.⁹ It is a neuronal biomarker leaked from injured neurons and detectable in the bloodstream.¹⁰ Tau protein is an intracellular axonal protein linked with microtubules that regulates their dynamic stability by phosphorylation, leading to phosphorylated tau (P-Tau). Following TBI, total tau (T-Tau) is released and can be detected as early as 6 hours.¹¹
As UCH-L1 and T-Tau are considered promising biomarkers, the current study aimed to evaluate their ability to predict the need for surgical intervention and neurological outcomes in patients with acute mild to moderate TBI.

Materials and Methods

1. Study Design and Patients: The current study was conducted in the ED of Alexandria Main University Hospital (AMUH), Egypt. The study protocol was approved by the Research Ethics Committee of Alexandria Faculty of Medicine, Alexandria University, Egypt (Approval number: 0201383/08/20, IRB number: 00012098, FWA number: 00018699). Informed consent was obtained from each patient or his/her legally authorized representatives before participating in the study. The study involved 85 patients, admitted with mild to moderate TBI. 1.1 Inclusion Criteria: (1) Age ≥18 years (2) History of a blunt closed head trauma followed by loss of consciousness (LOC), amnesia, or vomiting (3) Initial GCS of 9-15 on admission (4) Presentation to the ED within 24 hours of the initial trauma 1.2 Exclusion Criteria: (1) History of a neurological disease (2) Head trauma as a secondary event e.g., after syncope or seizure (3) The time of injury was unknown TBI was classified as mild if the patient had a LOC for up to 30 minutes, confusion, or disorientation lasting < 24 hours, an initial GCS of 13–15, or posttraumatic amnesia (PTA) of < 24 hours. On the other hand, TBI was classified as moderate if the patient had a LOC of > 30 minutes but < 24 hours, confusion or disorientation for > 24 hours, an initial GCS of 9–12, or PTA for > 24 hours but < 7 days. 2. Biomarkers Measurement: A venous blood sample (5 ml) was collected from each TBI patient (within 24 hours of the trauma). Sandwich enzyme-linked immunosorbent assay (ELISA) kits supplied by Innova Biotech, Beijing, China (catalog number: In-Hu4136) and Sunred Biotech, Shanghai, China (catalog number: 201-12-4295) were used to measure the levels of UCH-L1 and T-Tau, respectively. The lower limit of quantification was 0.1 ng/ml for UCH-L1 and 1.5 pg/ml for T-Tau according to the manufacturer’s protocol. 3. TBI Outcome: Outcome measures included the need for surgical intervention and neurological outcome. – Neurosurgical intervention was defined as the need for craniotomy or elevation of a skull fracture.⁵ – Neurological outcome was assessed 3 months post-injury using Glasgow Outcome Scale (GOS) during the patient’s follow-up visit to the hospital or by telephone survey with one of the patient’s close relatives. The investigator who conducted the telephone survey was blinded to the laboratory results. GOS categorizes the outcomes of patients after TBI, as follows.¹² • Good recovery (GOS =5): resumption of daily life activities • Moderate disability (GOS =4): disabled but independent from others • Severe disability (GOS =3): disabled and dependent on others for daily support • Vegetative state (GOS =2): minimal responsiveness • Death (GOS =1) For statistical analysis, the neurological outcome was dichotomized into good outcome (GOS =5) and poor outcome (GOS <5). Ethical Approval Ethics Committee approval for the study was obtained. 4. Statistical Analysis: The sample size required for this study was calculated with PASS software version 20 using independent t-test with an alpha error of 5% and a study power of 80%. This was done using data from a previous study.¹³ Statistical analysis was done using IBM SPSS software version 25.0 (Armonk, NY: IBM Corp). The Kolmogorov-Smirnov test was used to determine the distribution of data. The Mann-Whitney test was used to compare between the two groups. Receiver operating characteristic (ROC) curves were generated to assess the performance of UCH-L1 and T-Tau. Acceptable performance was defined as an area under the curve (AUC) of more than 50%, and the best performance was defined as an area of 100%. Cut-off values were obtained from the ROC curves using the Youden index to maximize both sensitivity and specificity.

Results

1. Characteristics of TBI Patients (Table 1):The study included n = 85 TBI patients. The majority were males (82.4%). The age ranged from 18 to 72 years with a mean of 35.8 years. Vehicle accident was the most common cause of TBI (55.3%).
According to GCS, 81.2% of patients had mild TBI (GCS 13–15) while 18.8% had moderate TBI (GCS 9–12). Clinical manifestations included vomiting in 24.7%, LOC and vomiting in 21.2%, and LOC with PTA in 18.8%. Intracranial CT lesions (extradural hemorrhage, subdural hemorrhage, cerebral contusion, subarachnoid hemorrhage) were found in 38.8% of patients.
Surgical intervention was required in nearly 13% of patients. GOS assessed 3 months after injury showed that 85.9% had good outcomes (GOS = 5), while 14.1% had poor outcomes (GOS < 5). No deaths (GOS = 1) were reported.2. UCH-L1 and T-Tau Results:2.1 Neurosurgical Intervention:Table 2 compares UCH-L1 and T-Tau levels in patients requiring surgical intervention versus those treated medically. Median UCH-L1 levels were 11 and 8 ng/ml, respectively, while median T-Tau levels were 140.1 and 57.2 pg/ml, respectively. There was a statistically significant difference between medians of both biomarkers (p<0.001).
ROC curves showed that T-Tau (AUC = 0.909) outperformed UCH-L1 (AUC = 0.872) in distinguishing patients requiring surgical intervention.
– UCH-L1 cut-off: 9 ng/ml (accuracy 82.4%, sensitivity 90.9%, specificity 81.1%, NPV 98.4%)
– T-Tau cut-off: 125.7 pg/ml (accuracy 89.4%, sensitivity 81.8%, specificity 90.5%, NPV 97.1%) (Figure 1).2.2 Neurological Outcome:Table 3 compares UCH-L1 and T-Tau serum levels in patients with poor outcome (GOS < 5) versus good outcome (GOS = 5) at 3 months. Median UCH-L1 levels were 10.75 and 8 ng/ml, respectively, while median T-Tau levels were 137.95 and 57.2 pg/ml, respectively. There was a statistically significant difference between medians of both biomarkers (p<0.001).
ROC curves showed that T-Tau (AUC = 0.916) outperformed UCH-L1 (AUC = 0.878) in discriminating poor versus good outcomes.
– UCH-L1 cut-off: 9 ng/ml (accuracy 83.5%, sensitivity 91.7%, specificity 82.2%, NPV 98.4%)
– T-Tau cut-off: 125.7 pg/ml (accuracy 90.6%, sensitivity 83.3%, specificity 91.8%, NPV 97.1%) (Figure 2).

Discussion

TBI remains one of the major causes of mortality and disability worldwide. Accurate prediction of outcome in TBI cases is difficult because physicians depend on GCS and CT. Both tools have limitations; GCS may be under- or over-estimated, while CT is not sensitive to minute neural and structural changes after TBI.⁴ Conversely, fluid biomarkers are more accurate and objective tools to assess severity and predict long-term sequelae.¹⁴ However, no biomarker has been approved for clinical use except S-100B.¹⁵
This study evaluated the ability of UCH-L1 and T-Tau to predict the need for neurosurgical intervention and 3-month neurological outcome in acute mild to moderate TBI. These biomarkers were chosen because TBI pathophysiology is complex: UCH-L1 measures neuronal injury, while T-Tau measures axonal injury.⁷ The study focused on mild to moderate trauma due to limited sensitivity of GCS and CT in these patients.¹⁶ Pediatric patients were excluded as TBI pathophysiology differs in children.¹⁷ Sandwich ELISA was used to measure serum levels of UCH-L1 and T-Tau, as it is reliable, widely available, sensitive, specific, and inexpensive compared to other methods.^18-19 Previous studies also used ELISA kits for biomarker measurement in TBI.^20-21
In this study, serum UCH-L1 levels were significantly higher in patients requiring neurosurgical intervention. Its discriminative ability was very good (AUC = 0.872), consistent with Papa et al. (2012) who reported AUC = 0.860.¹³ UCH-L1 levels were also significantly higher in patients with poor outcome (GOS < 5) than in those who recovered (GOS = 5). This agrees with Takala et al. (2016) who studied 324 patients using GOS/GOS-E,²² and Mondello et al. (2016) who found elevated UCH-L1 in pediatric patients with unfavorable outcomes.²³ The predictive performance in this study (AUC = 0.878) was similar to Mondello (AUC = 0.86) and better than Takala (AUC = 0.727). Korley et al. (2022) reported lower AUC = 0.610 for incomplete recovery at 6 months, possibly due to inclusion of severe TBI and longer follow-up.²⁴
Regarding T-Tau, serum levels were significantly higher in patients requiring surgery. Compared to UCH-L1 (AUC = 0.872), T-Tau showed better predictive ability (AUC = 0.916). For 3-month outcome, T-Tau levels were significantly higher in patients with poor outcome, consistent with Rubenstein et al. (2017) who correlated plasma T-Tau/P-Tau with functional outcome.²⁵ However, predictive performance in this study (AUC = 0.909) was better than Rubenstein (AUC = 0.770), possibly due to different measurement methods (ultra-high sensitivity laser-based immunoassay).
Advantages of this study include evaluation of T-Tau for neurosurgical intervention and outcome prediction, which has been inadequately studied, and comparison of two biomarkers reflecting different injury mechanisms. Findings suggest both UCH-L1 and T-Tau are potential prognostic biomarkers, with T-Tau showing superior performance. Further studies with larger sample sizes are recommended to confirm their reliability in acute mild to moderate TBI.

Conclusion

This study revealed that serum levels of UCH-L1 and T-Tau were significantly high in TBI patients who required neurosurgical intervention and in patients who had poor outcome. Measuring the serum levels of UCH-L1 and T-Tau, on admission to the ED, could be used for precise prediction of outcome in patients with acute mild to moderate TBI. However, T-Tau could be a better prognostic TBI biomarker as it was more accurate than UCH-L1.

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