Background Moderate joint loading is essential to maintain cartilage health and function but the impact of immobilization on articular cartilage in healthy individuals is not well understood. One established biomarker for monitoring cartilage metabolism in relation to joint degeneration is cartilage oligomeric matrix protein (COMP)1 which is sensitive to physiological loading2-4 and 14-days of immobilization5.
Objectives To analyze the effect of 21-days of head down tilt bed rest (HDT-BR) (Study1) and 5.5 months of microgravity (Study 2) on serum COMP concentration.
Methods Study 1: Twelve healthy male subjects (34±8 yrs) participated in a 21-days HDT-BR study performed in a cross-over design. HDT-BR-only was the control (CON) condition. The intervention was resistive vibration exercise (RVE) alone or in combination with a nutrition intervention (NEX). 11 blood samples were collected before, during and after HDT-BR. Study 2: preliminary results of two astronauts will be presented. Blood samples were collected before and after 5.5 months on the International Space Station. Blood samples for both studies were taken in the morning after overnight-fast and 30 minutes supine rest. Biomarker concentrations were analyzed using commercial enzyme-linked immunosorbent assay (ELISA). Statistical analysis (IBM SPSS Statistics, 19.01) was performed using repeated measures ANOVA (p<0.05).
Results Study 1: Serum COMP concentration decreased with the first day of HDT (-24.7±12.5%; p<0.05). Concentrations returned to baseline levels after subjects were mobile again. RVE and NEX interventions did not affect this result (NEX: - 14.3±16.7%; RVE: -15.7±9.2%). Study 2: Preliminary results (n=2) indicate a high increase (+39.9%; + 13.3%) in serum COMP concentration 7 days after return to gravity. Levels remain elevated until 30 days after landing.
Conclusions These results suggest that cartilage ECM is sensitive to unloading and immobilization may initiate catabolic processes in cartilage metabolism. Investigating cartilage health in response to a stay in microgravity is a unique model and will broaden the understanding of cartilage metabolism. Future research should investigate sufficient exercise countermeasures in order to minimize negative effects of immobilization on cartilage health.
Saxne et al. Br J Rheumatol 1992; 31(9):583-91.
Neidhart et al. Osteoarthritis Cartilage 2000, 8(3):222–9.
Mündermann et al. Osteoarthritis Cartilage 2005, 13(1), 34–8.
Niehoff et al. Osteoarthritis Cartilage 2009, 19(8):1003-10.
Liphardt et al. Osteoarthritis Cartilage 2009, 17(12):1598–603.
Disclosure of Interest None declared