Tartrate-Resistant Acid Phosphatase 5a Activity as a Novel Biomarker for Flare of Systemic Lupus Erythematosus

Tartrate-resistant acid phosphatase (TRAP) 5a is strongly expressed in inflammatory macrophages. Serum TRAP 5a protein concentration increases in patients with chronic inflammatory diseases such as end-stage chronic kidney disease, rheumatoid arthritis and systemic lupus erythematosus (SLE). SLE can involve the joints, kidneys, mucous membrane and blood vessel walls. In this cross-sectional, proof-of-concept study, patients with SLE were analyzed for substantiating our hypothesis that TRAP 5a activity and protein are potential biomarkers for SLE flare. Forty-one (41) female patients with SLE were enrolled: 18 had SLE flare and 23 had stable SLE. In addition, 20 healthy women without SLE served as controls. Serum TRAP 5a activity and protein concentration and C-reactive protein concentration were evaluated in all participants. Serum TRAP 5a activity was significantly higher in patients with SLE flare than in those with stable SLE (P < 0.0001). However, serum TRAP 5a activity was significantly lower in patients with stable SLE than in controls (P = 0.0135). Serum TRAP 5a protein concentration was significantly higher in SLE patients with and without flare than in controls (P = 0.005 and 0.0012, respectively). Furthermore, serum TRAP 5a protein concentration was slightly higher in patients with SLE flare than in those with stable SLE (P = 0.0634). To compare TRAP 5a activities and protein concentrations between the flare and stable groups, receiver operating characteristic curves were constructed; the areas under these curves were 0.9662 (P < 0.0001) and 0.6763 (P = 0.0055) for the activities and protein concentrations, respectively. Serum TRAP 5a protein concentration increases in patients with SLE and tends to increase further when patients develop the flare. TRAP 5a activity was lower than normal in patients with stable SLE, but it increased significantly after the flare developed. These data suggest that TRAP 5a activity and protein concentration are potential biomarkers for SLE flare..