Study On Serum Metabolomics Of Adolescent Idiopathic Scoliosis And General Balance After Selective Fusion

Background and objectiveAdolescent idiopathic scoliosis (AIS) is the most common form of scoliosis. Patients with severe deformity would suffer a series of physical and metal dysfunction. Early diagnosis would make the patients have more chance for consecutive treatment, hence reducing surgical rate. So far, the diagnosis and screening of AIS still mainly depend on the asymmetry appearance of patients and radiographic tests. Useful diagnostic biomarkers for early diagnosis and screening of AIS are still absent. The development of metabonomics enables researchers to detect a large number of metabolites quantitatively through an untargeted searching approach, providing a new way in discovering disease related biomarkers. Thus, we conducted serum metabonomic study of AIS in the basic research section of the whole study. The main objective was to discover potential diagnostic biomarkers of AIS and to explore the mechanism of the "presumed abnormal metabolic pathway" of AIS.One of the main aims of correction surgery of AIS is reconstruction trunk balance. Thoracolumbar/lumbar (TL/L) AIS is a series of scoliotic deformities characterized as having the main structural curve in the TL/L region. Most of this type of scoliosis can be treated by selective TL/L curve fusion with satisfactory results. After selective TL/L curve fusion, most of the lumbar segments were fused and most of the thoracic segments were left unfused. Thus, we studied the effect of unfused segments in the reconstitution of coronal balance in the coronal plane and risk factors for an increased PJA in the sagittal plane.Methods(1) The metabolic profiles of serum samples from 30 AIS patients and 31 healthy controls in discovery set were acquired using UPLC/QTOF-MS. Differential metabolites were identified through multivariate statistical analysis and related metabolic pathways were analyzed. Then the diagnostic capabilities of the differential metabolites were evaluated through ROC analysis to discover potential diagnostic biomarkers. To validate the findings of these diagnostic biomarkers, serum samples of 31 AIS patients and 44 healthy controls were analyzed by UPLC/QTOF-MS as the replication set. At last, key enzymes of the abnormal metabolic pathway of AIS were tested.(2) TL/L AIS patients who underwent selective posterior TL/L curve fusion in our hospital with a minimum of 2 years of follow-up period were retrospectively analyzed. Changes of coronal trunk shift (C7PL-CSVL) during the follow-up period were studied and multiple linear regression analysis was performed to determine its correlation with changes of upper and lower curve of unfused thoracic segments, instrumented segments angle, distal unfused segments angle, and coronal sacral inclination.(3) TL/L AIS patients that underwent selective posterior TL/L curve fusion in our hospital with upper instrumented vertebrae (UIV) below T8 were identified. The folloe-up period was at least 2 years. Changes of proximal junctional angle (PJA) during the follow-up period were studied and multiple linear regression analysis was performed to determine the relation of PJA changes during follow-up and eight potential risk factors, including locations of UIV, locations of lower instrumented vertebra (LIV), length of fusion segments, types of pedicle screw alignment, lumbar lordosis (LL) at first erect after surgery, LL changes before and after surgery, sagittal vertical axis (SVA) at first erect after surgery and SVA changes before and after surgery.Results(1) Seven differential metabolites of AIS were identified through UPLC-Q-TOF/MS analysis in discovery set, including PC(40:4) (1),2-Hexenoylcarnitine (2), beta-D-Glucopyranuronic acid(3), DG(38:9)(4), MG(20:3)(5), LysoPC(18:2) (6) and LysoPC(16:0) (7). These defferential metabolites involved glycerophospholipid metabolism, glycerolipid metabolism and fatty acid metabolism. ROC analysis showed that except LysoPC(18:2), the other six differential metabolites repsented good diagnostic accuracy with the AUC reaching 0.7-1, which suggesting these metabolites were suitable as diagnostic biomarkers. UPLC-Q-TOF/MS analysis in replication set further validated the abnormal levels of these 6 potential biomarkers in AIS patients. Serum lecithin:cholesterol acyltransferase activity was performed using fluorescent enzyme-linked immune sorbent assay, showing no significant differential expression in AIS patients (P=0.812). Significant higher expressions of hormone-sensitive lipase (HSL) and adipose triacylglycerol lipase (ATGL) in adipose tissue were observed in AIS patients by RT-PCR assays.(2) A total of 43 patients were included in the coronal balance reconstitution study. Preoperative and first erect radiographs demonstrated trunk shifts of 21.1 mm and 18.7 mm respectively, showing no significant differences (P=0.205). At the last follow-up, it compensated to 9 mm, which showed significant differences (P<0.01). Regression analysis of all patients showed that coronal trunk shift changes only correlated with distal unfused segment angle changes. Subgroup analysis based on the magnitude of preoperative thoracic curve also found that only distal unfused segments had an impact on coronal balance reconstitution. However, subgroup analysis based on the flexibility of preoperative thoracic curve showed that both proximal unfused thoracic segments and distal unfused lumbar segments contributed to coronal balance compensation in patients with a thoracic curve flexibility rate of more than 70%.(3) A total of 41 patients were included in the study of risk factors of increased PJ A. PJA was increased from 5.5mm immediately after surgery to 10.8mm at the last follow-up, showing statistical significant differences (P< 0.0001). Regression analysis showed that locations of LIV, LL changes before and after surgery and SVA changes before and after surgery were risk factors for increased PJA. Pearson correlation test showed that postoperative LIV inclination was significantly correlated with PJA changes.Conclusions(1) 7 differential metabolites were identified in serum metabolomic study of AIS,6 of which could be used as potential diagnostic biomarkers. Metabolic pathway analysis suggested that significantly perturbed lipid metabolism occurred in AIS. Abnormal lipid metabolism was further validated by increased expressions of HSL and ATGL in adipose tissue of AIS patients. We speculated that abnormal lipid metabolism of AIS might be the manifestation of abnormal neuroendocrine system.(2) The reconstitution of coronal balance was mainly compensated by distal unfused segments after selective posterior fusion of TL/L idiopathic scoliosis. The effect of unfused thoracic segments in coronal balance reconstitution mainly depended on its flexibility.(3) Location of LIV above or equal to L3, higher postoperative LL and deteriorative negative SVA with surgery were potential risk factors for increased PJA during follow-up. Postoperative LIV inclination more than 5° might be an indicator for an increase in PJA.