Original ArticleMetabolic Changes in Serum in the Rat Model of Cauda Equina Injury
Introduction
Cauda equina injury (CEI) is a nerve injury caused by a variety of congenital or acquired oppression of the cauda equina, with absolute or relative stenosis of the lumbar spinal canal.1 CEI may lead to cauda equina syndrome, marked by sensory and motor dysfunction and micturition, defecation, and sexual dysfunction, which seriously affect patients' physical functioning and quality of life.2
Laminectomy and discectomy are the main treatments for CEI, but surgical outcomes are not always satisfactory.3 Recent studies have shown that once the diagnosis of CEI is confirmed, emergency surgical treatment will provide better improvement in lower limb function.4, 5 Therefore, earlier diagnosis of CEI is particularly important to achieving a better surgical outcome.
However, distinct from central nervous system injury, there are usually no obvious clinical symptoms in the early stages of CEI. The cauda equina can be visualized by contrast-enhanced computed tomography scan and magnetic resonance imaging6; however, these clinical imaging techniques could only provide evidence of compression of the cauda equina, not of damage to the cauda equina.2 Therefore, a definitive diagnosis cannot be made based on clinical symptoms or radiography data in the early stages of CEI.
Metabolomics has been widely used for identifying biomarkers and providing insight into the pathogenesis of central nervous system injury. In a previous study, we identified potential biomarkers of CEI in the cauda equina tissue.7 When the cauda equina is injured, some metabolites may be released into blood and activate anabolic and metabolic pathways to protect from the stress and prepare nutrition for the subsequent nerve reconstruction. In this study, we used ultra-high-performance liquid chromatography–quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF/MS)–based metabolomics analysis to analyze small-molecule metabolites in the serum and identify potential biomarkers of early-stage CEI.
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Chemicals and Reagents
Methanol and acetonitrile of chromatographic grade were purchased from Merck (Darmstadt, Germany). Formic acid of HPLC grade was purchased from Fluka (Buchs, Switzerland). Glyoxylic acid was purchased from TCI (Tokyo, Japan), and mixed with sodium hydroxide to form glyoxylate. Ultrapure water was prepared with a Milli-Q water purification system (EMD Millipore, Billerica, Massachusetts, USA).
Animal Experiments and Sample Collection
All experiments were approved by the Animal Ethics Committee of the Navy Medical University and were
Analysis of Blood Metabolomics Profiles in CEI
Total ion chromatograms in blood samples from 5 groups of 50 CEI rats were obtained, including positive ion mode (ESI+) and negative ion mode (ESI−). We analyzed and selected metabolites with significant changes in blood levels after CEI. First, we used supervised multivariate statistical analysis (PCA) to identify and exclude outliers, and observed that the QC samples were closely aggregated, which verified the good stability of the experimental method. We then applied PLS-DA to determine the
Discussion
The cauda equina is a bridge connecting the central and peripheral nervous systems, connecting with the dorsal root ganglion, pseudo-unipolar neurons, and spinal cord neurons. Owing to its unique anatomic structure, the cauda equina is susceptible to injuries secondary to lumbar spinal stenosis, lumbar disc herniation, or vertebral column fractures. The appearance of symptoms of CEI, such as micturition, defecation, and sexual dysfunction, heralds a poor prognosis after surgical treatment. Most
Conclusions
Metabolomics is an effective means of identifying metabolites that change after disease and can provide insight into the pathogenesis and metabolic processes of the disease from a systematic perspective. In this study, metabolomic profiling was performed using UHPLC/Q-TOF-MS to analyze the metabolic effects of compression of the cauda equina. CEI significantly affects energy metabolism, lipid metabolism, amino acid metabolism, and nucleotide metabolism. In this study, we identified 57 potential
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Conflict of interest statement: The work was supported by the National Scientific Foundation of China (81802186, 81871828, and 81650031).
Bin Zhang, Ran Yan, and Jun Lu contributed equally to this work and should be considered co–first authors.