Osteopontin and disease activity in patients with recent-onset systemic lupus erythematosus: results from the SLICC Inception Cohort

Objective: In cross-sectional studies, elevated osteopontin (OPN) levels have been proposed to reflect, and/or precede, progressive organ damage and disease severity in systemic lupus erythematosus (SLE). We aimed, in a cohort of recent-onset SLE, to determine whether raised serum OPN levels precede damage and/or associate with disease activity or certain disease phenotypes.

Methods: We included 344 patients from the Systemic Lupus International Collaborating Clinics (SLICC) Inception Cohort who had 5-years of follow-up data available. All patients fulfilled the 1997 American College of Rheumatology (ACR) criteria. Baseline sera from patients and from age- and sex-matched population-based controls were analysed for OPN using ELISA. Disease activity and damage were assessed at each annual follow-up visit using the SLE Disease Activity Index 2000 (SLEDAI-2K) and the SLICC/ACR damage index (SDI), respectively.

Results: Compared to controls, baseline OPN was raised fourfold in SLE cases (p<0.0001). After relevant adjustments in a binary logistic regression model, OPN levels failed to significantly predict global damage accrual defined as SDI≥1 at 5 years. However, baseline OPN correlated with SLEDAI-2K at enrolment into the cohort (r=0.27, p<0.0001), and patients with high disease activity (SLEDAI-2K≥5) had raised serum OPN (p<0.0001). In addition, higher OPN levels were found in patients with persistent disease activity (p=0.0006), in cases with renal involvement (p<0.0001) and impaired estimated glomerular filtration rate (p=0.01).

Conclusion: The performance of OPN to predict development of organ damage was not impressive. However, OPN associated significantly with lupus nephritis and with raised disease activity at enrolment, as well as over time.