Metabolomic serum profiling after ACL injury in rats: A pilot study implicating inflammation and immune dysregulation...

ACL rupture is a major risk factor for post-traumatic osteoarthritis (PTOA) development. Little information exists on acute systemic metabolic indicators of disease development. Thirty-six female Lewis rats were randomized to Control or noninvasive anterior cruciate ligament rupture (ACLR) and to three post-injury time points: 72 h, 4 weeks, 10 weeks (n = 6). Serum was collected and analyzed by ¹ H nuclear magnetic resonance (NMR) spectroscopy and combined direct injection and liquid chromatography (LC)-mass spectrometry (MS)/MS (DI-MS). Univariate and multivariate statistics were used to analyze metabolomic data, and predictive biomarker models were analyzed by receiver operating characteristic (ROC) analysis. Topological pathway analysis was used to identify perturbed pathways. Two hundred twenty-two metabolites were identified by ¹ H NMR and DI-MS. Differences in the serum metabolome between ACLR and Control were dominated by medium- and long-chain acylcarnitine species. Further, decreases in several tryptophan metabolites were either found to be significantly different in univariate analysis or to play important contributory roles to multivariate model separation. In addition to acylcarnitines and tryptophan metabolites, glycine, carnosine, and D-mannose were found to differentiate ACLR from Control. Glycine, 9-hexadecenoylcarnitine, trans-2-Dodecenoylcarnitine, linoelaidyl carnitine, hydroxypropionylcarnitine, and D-Mannose were identified as biomarkers with high area under ROC curve values and high predictive accuracies. Our analysis provides new information regarding the potential contribution of inflammatory processes and immune dysregulation to the onset and progression of PTOA following ACL injury. As these processes have most commonly been associated with inflammatory arthropathies, larger-scale studies elucidating their involvement in PTOA development and progression are necessary. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1969-1979, 2018.