Metabolic phenotypes reflect patient sex and injury status: A cross-sectional analysis of human synovial fluid

Objective Osteoarthritis is a heterogeneous disease. The objective was to compare differences in underlying cellular mechanisms and endogenous repair pathways between synovial fluid from male and female participants with different injuries to improve current understanding of the pathophysiology of downstream post-traumatic osteoarthritis. Design Synovial fluid from n=33 knee arthroscopy patients between 18 and 70 years with no prior knee injuries was obtained pre-procedure and injury pathology assigned post-procedure. Synovial fluid was extracted and analyzed via liquid chromatography-mass spectrometry metabolomic profiling to examine differences in metabolism between injury pathologies (ligament, meniscal, and combined ligament and meniscal) and patient sex. Samples were pooled and underwent secondary fragmentation to identify metabolites. Results Different knee injuries uniquely altered synovial fluid metabolites and downstream pathways including amino acid, lipid, and inflammatory-associated metabolic pathways. Notably, sexual dimorphic metabolic phenotypes were examined between males and females and within injury pathology. Cervonyl carnitine and other identified metabolites differed in concentrations between sexes. Conclusions These results suggest that different injuries and patient sex are associated with distinct metabolic phenotypes. Considering these phenotypic associations, a greater understanding of metabolic mechanisms associated with specific injuries, sex, and post-traumatic osteoarthritis development may yield data regarding how endogenous repair pathways differ between male and female injury types. Ongoing metabolomic analysis of synovial fluid in injured male and female patients can be performed to monitor post-traumatic osteoarthritis development and progression.