THU0329 OPG/RANK/RANKL in pathogenesis of osteoporosis of juvenile idiopathic arthritis (JIA) subtypes

Abstract

Background A decrease in bone mass has been described in a high percentage with increased risk of osteoporosis in JIA subtypes. The pathogenesis of bone loss in active JIA is complex, and results in reduced bone mineral density. Recent data have indicated an overlapping pathway between bone biology and biology of inflammation giving impression that inflammation may have a role in pathology of osteoporosis. Understanding the role of OPG/RANK/RANKL modulation in pathogenesis of bone loss among JIA subtypes will hold the key for identification of patients at risk and for management of osteoporosis. Objectives To evaluate the role of receptor activation of nuclear factor kB (RANK)/receptor activator of nuclear factor kB ligand (RANKL)/osteoprotegerin (OPG) modulation in juvenile idiopathic arthritis (JIA) subtypes with and without bone erosions. Methods Seventy children presenting JIA subtypes were recruited for the study and were chosen according to ILAR, 2001 criteria. They were compared with thirty healthy controls of matched age, sex, and ethnicity. Both groups had the average dietary intake of calcium products and sun exposure. Clinical presentations, laboratory investigations, and treatments used especially corticosteroids were recorded. JIA subtypes were oligo articular, polyarticular RF negative, RF positive, systemic onset JIA (SOJIA), enthesitis related arthritis (ERA) and psoriatic (PsA). All involved articulations were assessed by plain radiography for juxtaarticular osteoporosis and bone erosions. Disease activity was measured by Juvenile Arthritis Disease Activity Score (JADAS-27). Serum levels of OPG, RANK and RANKL were measured with estimation of OPG/RANKL ratio, using an enzyme-linked immunosorbent assay (ELISA). Results A significant low serum concentration of OPG was found in all JIA subgroups. There was a significant increase in serum level of RANKL, and a significant decrease of OPG/RANKL ratio. OPG/RANKL ratio was significantly lower in SOJIA, active polyarticular JIA and ERA than other groups within the subtypes. A significant low OPG/RANKL ratio was found in patients with prolonged steroid use and those with erosions. To our knowledge, this research is the first one studied these biomarkers in JIA subtypes, including ERA. Conclusions OPG/RANKL ratio can be an early predictor of increased bone resorption, and may be a valuable biomarker for bone damage in JIA subtypes. Systemic onset juvenile idiopathic arthritis, active polyarticular juvenile idiopathic arthritis and enthesitis related arthritis are at higher risk for osteoporosis. Disclosure of Interest None Declared