Fig. 1

Lipid distribution in human serum and synovial fluid. Total phospholipid (PL) and sphingolipid (SL) content and the levels of PL and SL classes in synovial fluid (SF) and serum are depicted for 13 SF and 31 serum controls, 29 patients with early OA (eOA), and 29 patients with late OA (lOA). PL and SL species were quantified by ESI-MS/MS, and data are presented as box plots with median, interquartile range, and outliers. The solid polylines connect eOA group medians, illustrating elevated levels in serum compared with the corresponding SF levels. Statistically significant differences were determined by Wilcoxon´s rank sum test and are indicated by * if their FDR-adjusted p-values are < 0.05. Precise PL and SL concentrations, serum/SF ratios, and statistical results are listed in Supplementary Table S1. PC, phosphatidylcholine; PC O, ether-linked phosphatidylcholine; LPC, lysophosphatidylcholine; SM, sphingomyelin; PE, phosphatidylethanolamine; PE P, phosphatidylethanolamine-based plasmalogen; HexCer, hexosylceramide; Cer, ceramide