Serum COMP concentrations in response to 5 days of immobilization in female and male participants

Introduction: In healthy male participants, bed rest immobilization leads to alterations in serum cartilage biomarker concentrations [1], while in females this effect has not been investigated to date. Cartilage oligomeric matrix protein (COMP) is a mechanosensitive biomarker of cartilage degeneration [2]. Dry immersion (DI) is an immobilization model that simulates a support-free environment and restricts movement. We aimed to examine serum COMP (sCOMP) concentrations in females compared to males during 5 days of DI immobilization.
Methods: This study was conducted at the Institute de Médecine et de Physiologie Spatiales (MEDES), Toulouse, France. 18 healthy females (29±5 years, 165±6 cm, 59±6 kg) and 19 males (28±4 years, 177±4 cm, 72±7 kg) underwent 4 days of baseline data collection (BDC), 5 days of DI (24 hrs/day), and 3 days of recovery (R) (Figure 1). Fasting venous blood samples were collected on BDC-50h, BDC-26h, DI46h, DI118h and R+46h. sCOMP concentrations were analyzed by commercially available ELISA (BioVendor R&D®). Repeated measures ANOVA (LSD post-hoc test) with sex as between-subjects factor was performed.
Results: sCOMP levels did not differ between females and males (p=0.831, Table 1). Consequently, they were pooled for further analysis. DI led to a substantial decrease in sCOMP levels (p<0.001) and a subsequent increase (p<0.001) during remobilization to BDC levels.
Conclusion: sCOMP concentrations were clearly reduced after 46hrs of DI, with no sex differences, indicating perturbed cartilage metabolism. The observed reduction in sCOMP was more pronounced during DI (-35%) compared to the effect measured in a previous 5 days bed rest study (-23%) [1].
[1] Liphardt AM et al., J Orthop Res. 38:2373-2382, 2020
[2] Tseng S et al., Biomark Insights. 4:33-44, 2009
Acknowledgements: European Space Agency, Federal Ministry of Economic Affairs and Energy, Germany (DLR 50WB2021, DLR 50WB2022), participating volunteers, MEDES study team, Toulouse, France.












Figure 1: Study timeline with blood sampling time points. BDC: Baseline Data Collection (grey area), DI: Dry Immersion (blue area), R: Recovery (green area).





Table 1: Absolute sCOMP concentrations [ng/mL] at different sampling time points, displayed separately for female and male participants, as well as overall concentrations. Values are presented as means and 95% CI. *p<0.001 significantly different to BDC and R time points.
Sampling time points BDC-50h BDC-26h DI46h DI118h R+46h
Female N=18 410 (328-492) 397 (321-472) 255 (202-308) 237 (190-283) 385 (312-457)
Male N=19 429 (330-527) 402 (316-488) 253 (196-311) 229 (172-286) 455 (356-554)
Overall N=37 420 (358-481) 400 (345-454) 254 (217-292)* 233 (198-268)* 421 (361-481)