Identification of Disease Specific Metabolic Fingerprints in Early Osteoarthritis

Abstract

Reasons for performing study Synovial fluid ( SF ) is located in joint cavities, tendon sheaths and bursae. In joints it comprises a serum filtrate with additional contributions from articular cartilage, synovium and bone. Low molecular weight metabolites represent the end product of the cell regulatory processes. Synovial fluid represents a potential source of disease specific metabolites that could aid in the understanding of the pathogenesis of osteoarthritis ( OA ) and be used in its early diagnosis. Objectives We hypothesise that there are different metabolomic profiles that can be identified in early OA SF and some of these metabolites are potential biomarkers. Study design Cross‐sectional study. Methods Synovial fluid was used from the metacarpophalangeal joints of 9 normal and 9 OA Thoroughbred horses following macroscopic, microscopic and synovitis scoring. SF was analysed with Proton (1H)‐nuclear magnetic resonance ( NMR ) spectroscopy with a 600 MHz Avance III equipped with a cryoprobe and chilled sample‐jet autosampler. The software we use is Topsin 3.1 and IconNMR 4.6.7. The following methods were used in order to identify changes in lipids and small molecules; 1D Nuclear Overhauser Effect, Longitudinal Encode‐decode and Carr‐Purcell‐Meiboom‐Gill. Data analysis was undertaken using unsupervised statistical methods and Ingenuity Pathway Analysis ( IPA ). Results The results demonstrated clustering on principle component analysis between normal and OA samples. Seven metabolites were identified as significantly different in OA P<0.05; mobile lipid 1, methyl group, 2 lactates, proline and 2 citrates. Furthermore total lipid load correlated very closely to Mankin's scoring. Using IPA we identified metabolic pathways relating to altered glycolysis in early OA . Conclusions We identified the metabolic fingerprint of early OA which may allow for better phenotyping of disease states and thereby facilitate targeting of improved treatment regimes. Ethical animal research: Samples were collected at post mortem examination with informed owner consent. Sources of funding: Wellcome Trust and the MRC and Arthritis Research UK as part of the MRC – Arthritis Research UK Centre for Integrated research into Musculoskeletal Ageing ( CIMA ). Competing interests: None declared.