Serum lubricin levels in patients with juvenile idiopathic arthritis

Lubricin, encoded by the proteoglycan 4 (PRG4) gene, is mainly responsible for lubricating joints. However, there is expanding evidence on its involvement in inflammatory pathways. Juvenile idiopathic arthritis (JIA) is a heterogeneous group of chronic arthritides with an unknown origin in children aged below 16 years. It is characterized by chronic joint inflammation, including synovial inflammation, and may result in cartilage destruction. We aimed to determine whether serum lubricin levels are affected in JIA patients.

This cross-sectional study included children diagnosed with JIA and 28 healthy controls. The patients were divided into two groups according to the presence of remission at the time of study. Lubricin protein analysis was performed by the enzyme-linked immunosorbent assay method. Serum samples were obtained at the study enrollment, and lubricin levels were measured once, and compared between JIA patients and healthy controls, and between JIA patients with active disease and remission.

The study included 52 JIA patients (28 female, 24 male) and 28 healthy controls (18 female, 10 males). The mean age at study enrollment was 11.66 ±4.41 years and 12.72 ±4.52 years in the JIA patient and control groups, respectively. Although median serum lubricin level did not differ between JIA patients (median: 0.66 ng/μl, range: 0.02-3.85 ng/μl) and healthy controls (median: 0.52 ng/μl, range: 0.06-3.84 ng/μl), it was statistically significantly higher in patients with active disease (median: 1.58 ng/μ, range: 0.08-3.85 ng/μl) than both patients in remission (median: 0.57 ng/μl, range: 0.02-3.57 ng/μl) and healthy controls. A low degree positive correlation was also found between serum lubricin levels and erythroid sedimentation rate of the JIA patients (r = 0.383 and p = 0.011).

This is the first study investigating serum lubricin levels in JIA patients, and we found elevated serum lubricin levels in JIA patients with active disease. Further studies are needed to clarify our results.