To determine the possible role of the plasminogen activator (PA)/plasmin system in gouty arthritis.
We compared the antigenic values of urokinase-type PA (uPA), soluble uPA receptor (suPAR), and PA inhibitor type-1 (PAI-1) and the levels of matrix metalloproteinase-2 (MMP-2) and MMP-9 in 63 synovial fluid (SF) samples from knee joints of 38 patients with gouty arthritis and 20 SF samples from knee joints of 20 patients with osteoarthritis (OA).
The increases of uPA, suPAR, and PAI-1 antigenic values in SF were associated with increased levels of latent MMP-9 (pro-MMP-9) (p < 0.001, p < 0.001, p < 0.001, respectively) in gouty arthritis, whereas a correlation was not observed between uPA, suPAR, and PAI-1 antigenic values and MMP-2 levels. Increased uPA, suPAR, and PAI-1 antigenic values in gouty arthritis SF were also correlated to each other (p < 0.001, p < 0.001, p < 0.001). In gouty arthritis SF, no significant relations were observed between uPA and suPAR antigenic values and leukocyte, neutrophil, or monocyte counts, while increased values of PAI-1 corresponded closely with increased leukocyte and neutrophil counts (p = 0.005, p = 0.004). Significantly higher values of the uPA, suPAR, and PAI-1 (p < 0.001, p < 0.001, p = 0.012) appeared in SF of gouty arthritis than in SF from patients with OA.
These results show a correlation of the PA/plasmin system and MMP-9 in SF from patients with gouty arthritis, resulting in increased PA catalytic activity and contributing to inflammation in gouty arthritis.