Serum ubiquitin C‐terminal hydrolase L1 predicts cognitive impairment in patients with acute organophosphorus pesticide poisoning

Abstract Background To assess the usefulness of serum C‐terminal hydrolase L1 (UCH‐L1) level as a biomarker for predicting cognitive impairment in patients with acute organophosphorus pesticide poisoning (AOPP). Methods Two hundred and seven adult patients with AOPP were included in this study. Serum UCH‐L1 levels were assessed on admission (Day 1 postpoisoning) and on Days 3 and 7 postpoisoning. The associations between serum UCH‐L1 levels, other clinical predictors, and cognitive function evaluated on Day 30 postpoisoning were investigated. Results On multivariate analysis, serum UCH‐L1 levels on admission (odds ratio [OR] 1.889, 95% confidence interval [CI] 1.609‐3.082, P = 0.002) and 24‐hour APACHE II score (OR 1.736, 95% CI 1.264‐3.272, P = 0.012) were independent predictors of cognitive impairment on Day 30 postpoisoning. Based on the receiver operating characteristic curve, serum UCH‐L1 levels >5.9 ng/mL on admission predicted cognitive impairment on Day 30 postpoisoning with 86.1% sensitivity and 72.5% specificity (area under the curve, 0.869; 95% CI 0.815‐0.923). On admission [8.51 (6.53‐10.22) ng/mL vs 4.25 (2.57‐6.31) ng/mL, P < 0.001] and Day 3 [9.31 (7.92‐10.98) ng/mL vs 3.32 (2.25‐5.13) ng/mL, P < 0.001] and Day 7 [4.96 (3.28‐7.26) ng/mL vs 2.27 (1.55‐3.24) ng/mL, P < 0.001] postpoisoning, serum UCH‐L1 concentration was significantly higher in patients that developed cognitive impairment compared to those that did not. Conclusion This study demonstrates that serum UCH‐L1 level has potential as a novel biomarker for predicting cognitive impairment 30 days after AOPP.


| INTRODUC TI ON
Acute organophosphorus pesticide poisoning (AOPP) is an important public health problem. AOPP is associated with substantial human morbidity and mortality because of the widespread use of organophosphate compounds. 1 The nervous system is particularly sensitive to the effects of AOPP, which manifest as cognitive impairment, including deficits in information processing, sustained attention, memory, problem-solving, abstraction, flexibility of thinking, and depressed mood. 2,3 Patients experiencing cognitive impairment in AOPP may have long-lasting or irreversible cognitive and behavioral sequelae and an increased mortality rate. Thus, the identification of patients with AOPP who are at risk of cognitive sequelae could guide treatment decision-making.
Acute organophosphorus pesticide poisoning causes irreversible inhibition of acetylcholinesterase (AchE) leading to the accumulation of acetylcholine (Ach) at synapses and muscarine, nicotine, and central nervous system symptoms. Clinically, evidence of AOPP can be confirmed by measuring a decrease in blood AchE activity, which can also be used to monitor treatment response as a prognostic indicator.
However, cognitive impairment in AOPP is not always associated with decreased blood AchE activity, 4 and evidence for a relationship between blood AchE activity and impaired neurobehavioral function is limited. 5 Ubiquitin C-terminal hydrolase L1 (UCH-L1) is a neuron-specific enzyme that is highly abundant in the brain. 6 UCH-L1 is a deubiquitinating enzyme that is required for normal cognitive function. 7,8 UCH-L1 has been implicated in the pathophysiology of Parkinson's disease (PD), 9 Alzheimer's disease (AD), 10 Huntington's disease, 11 and epileptic seizures. 12 Increasingly, UCH-L1 is recognized as a biomarker of brain injury. Circulating UCH-L1 levels are significantly increased after acute neurological insults such as traumatic brain injury, subarachnoid hemorrhage, ischemic stroke, hypoxic-ischemic encephalopathy, and cardiac arrest, [13][14][15][16][17][18] and altered UCH-L1 expression is an indicator of brain injury severity and a predictor of neurological outcomes. 17,19 To the authors' knowledge, no studies have investigated the utility of serum UCH-L1 level as a predictor of cognitive impairment after AOPP. Therefore, this prospective study compared serum UCH-L1 levels in patients with and without cognitive impairment following AOPP to evaluate the utility of UCH-L1 for the prediction of cognitive impairment. All patients with AOPP were administered atropine, cholinesterase, diuretic, and anti-inflammatory agents. All patients underwent gastric lavage, catharsis, monitoring and maintenance of life-sustaining organs, and treatment for acid/base disturbance. Patients with severe poisoning underwent hemoperfusion once a day for at least 3 days.

| Determination of UCH-L1 in serum
Blood samples for assessment of serum UCH-L1 were collected within the first 24 hours of admission to hospital (Day 1 postpoisoning) and on Days 3 and 7 postpoisoning. Samples were centrifuged for 10 minutes at 1300 g and stored at −80°C until analysis. Serum UCH-L1 levels were measured using an enzyme-linked immunosorbent assay (ELISA) kit (Proteintech Group, Inc, USA), according to the manufacturer's instructions. The lower limit of UCH-L1 detection was 0.03 ng/mL. Each sample was assayed in duplicate, and the mean of the two measurements was used in the final analyses.
Researchers performing the assays were blinded to the patients' clinical information.

| Data analysis
Statistical analysis was performed using SPSS 16.0 (SPSS, Inc) and GraphPad Prism (version 5.01, Inc). Data are reported as counts and percentages for categorical variables and means ± standard deviation (SD) or median and interquartile range for continuous variables. Based on the MMSE, patients were divided into two groups: with or without cognitive impairment on Day 30 postpoisoning.
Between-group comparisons were conducted using the chi-square or Fisher's exact test for categorical variables and the Student's t test or the Mann-Whitney U test for continuous variables. Univariate logistic regression analysis was used to select potential predictors of cognitive impairment. Variables with a P value <0.05 in univariate logistic regression were retained for multivariate logistic regression analysis. Those variables that attained a P value of 0.05 were considered significantly associated with cognitive impairment after adjustment for the other investigated covariates. Predictive values, estimations of optimal cutoff points, and area under the curve (AUC) were calculated from receiver operating characteristic (ROC) curves.
All hypotheses were two-tailed, and P < 0.05 was considered statistically significant.

| Baseline characteristics of the study patients
Overall, 297 patients were eligible for this study, and 238 patients were included. Of these, 21 patients died, and ten were lost to fol-   (P < 0.001) (Figure 1). 24-h APACHE II score, blood lactate, and white blood cell count were also significantly higher in patients with AOPP and cognitive impairment (  (Figure 2).   UCH-L1 is a soluble protein localized in the cell body of neurons in the central nervous system that has important roles in the regulation of synaptic plasticity and learning and memory. 24 Circulating UCH-L1 has been identified as a biomarker specific to neuronal injury 16,25 as it is released into the circulation when the integrity of the blood-brain barrier (BBB) is disrupted. 26,27 In a piglet model, serum UCH-L1 predicted neuronal apoptosis induced by deep hypothermic circulatory arrest. 28 In observational studies, cerebrospinal fluid (CSF) and serum levels of UCH-L1 had utility as diagnostic and prognostic biomarkers of traumatic brain injury. 13,14,29 In patients with aneurysmal subarachnoid hemorrhage, elevated CSF levels of UCH-L1 correlated with neurological outcomes and mortality. 15 In patients with white matter lesions, increased serum UCH-L1 levels were correlated with white matter lesion severity. 30 Taken together, these data and findings from the present study suggest that serum UCH-L1 level has potential as a predictive marker for cognitive impairment after AOPP. This study showed that serum UCH-L1 levels >5.9 ng/mL could predict the development of cognitive impairment after AOPP with relatively high sensitivity and specificity.

| D ISCUSS I ON
These results are consistent with our previous report describing the prognostic value of serum UCH-L1 levels in acute carbon monoxide poisoning. 31 Other studies suggest optimal UCH-L1 values for predicting outcomes differ between disease types. In patients with traumatic brain injury, the UCH-L1 cutoff value for the prediction of poor outcomes was 1.03 ng/mL. 29 In patients with severe traumatic brain injury, the UCH-L1 cutoff value for in-hospital mortality was 1.89 ng/mL. 32 APACHE II scoring is a classification system that is used to evaluate the severity and prognosis of disease. 33  Further studies with larger sample sizes are warranted to validate our findings.

| CON CLUS ION
In conclusion, this study demonstrates that serum UCH-L1 level measured at the time of hospital admission has potential as a novel biomarker for predicting cognitive impairment 30 days after AOPP.