Lipid profile of human synovial fluid following intra‐articular ankle fracture

Abstract

This study characterizes the metabolic profile of synovial fluid after intra-articular ankle fracture with an emphasis on changes in the lipid profile. Bilateral ankle synovial fluid from 19 patients with unilateral intra-articular ankle fracture was submitted for metabolic profiling. Contralateral ankle synovial fluid from each patient served as a matched control. Seven patients participated in a second bilateral synovial fluid collection after 6 months. Random forest classification, matched pairs t-tests (α <0.01), repeated measures ANOVA with post-test contrasts (α <0.01), correlation to cytokines and matrix metalloproteinases, and fracture and injury classification analyses yielded key lipid biomarkers in synovial fluid following intra-articular fracture. Free fatty acids, sphingomyelins, and lysolipids demonstrated significant elevation in fractured ankles at baseline. Fatty acids and sphingomyelins showed a significant decrease 6 months post-surgery. Random forest analysis showed predominantly fatty acids differentiating between groups. Significant correlations included fatty acids, sphingomyelins, and lysolipids with inflammatory cytokines and matrix metalloproteinases. Fracture classification showed increased fatty acids, lysolipids, and inositol metabolites as fracture severity increased. Fatty acid and sn-1 lysolipid elevation could be detrimental to the joint, as these strongly correlated with matrix metalloproteinases and TNF-α. This elevation also suggests involvement of phospholipase A2, a potential target for therapeutic intervention. Together with elevated 2-hydroxyl fatty acids, these findings suggest elevated sn-1 lysolipids, sphingomyelins, and subsequent lipid metabolites in synovial fluid as biomarkers of ankle injury. Reversal of this signature after 6 months suggests temporary involvement of these metabolites in disease progression, although they may activate signaling pathways which drive progression to osteoarthritis.

Amino Acid Profile of Synovial Fluid Following Intra-articular Ankle Fracture

“…Lipid metabolites were also evaluated in a subset of patients 6 months postsurgery, but the acute elevation of many metabolites after injury had resolved by this time point. 23 These previous results were collected retrospectively using a patient-matched control data set, in which synovial fluid was collected from both the injured and contralateral ankles, and suggest that acutely elevated inflammatory mediators may activate metabolic pathways that then drive progression to PTOA.…”

“…Although these ankle fractures represent a range of severity, previous work was unable to detect discrete differences between fracture types with or without concurrent soft tissue injury. 23…”

“…Synovial fluid was obtained from both the injured and contralateral ankles at the time of surgery (mean = 17 days following fracture; range = 8 to 40 days) and again at 6 months postsurgery, following methods described previously. 23 Briefly, after lower extremity operative scrub and draping, lavage and arthrocentesis were performed on each ankle joint using an 18-gauge needle and 10-mL syringe filled with 7 mL of sterile saline. The needle was inserted using the anteromedial approach under fluoroscopic guidance, and the same 7 mL of fluid was used to lavage the ankle joint 3 times prior to sample collection for standardization and to ensure near-complete collection of all joint synovial fluid.…”

“…Previous work has characterized cytokines, 3 matrix metalloproteinases (MMPs), 3 and lipid metabolites 23 elevated in ankle synovial fluid in the acute phase following intra-articular fracture. Lipid metabolites were also evaluated in a subset of patients 6 months postsurgery, but the acute elevation of many metabolites after injury had resolved by this time point.…”

Regulation of Fatty Acid Oxidation by Twist 1 in the Metabolic Adaptation of T Helper Lymphocytes to Chronic Inflammation

“…In the inflamed synovial tissue of patients, CD4+ T lymphocytes persist despite low levels of oxygen and nutrients, and they are refractory to conventional immunosuppressive therapies . With respect to nutrients qualifying as a metabolic energy source, there is little glucose and glutamine in inflamed tissue, while fatty acids are readily available . Herein, we describe the metabolic adaptation of CD4+ T lymphocytes to this inflamed environment.…”