Immobilization by 21-days of bed rest causes changes in biomarkers of cartilage homeostasis in healthy individuals

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Objective To investigate the effects of 21 days bed rest immobilization (with and without exercise and nutrition intervention) on serum concentrations of cartilage homeostasis biomarkers in healthy individuals. Design Twelve male volunteers (age 34.2 ​± ​8.3 years; BMI 22.4 ​± ​1.7 ​kg/m 2 ) participated in 6 days of baseline data collection (BDC), 21 days of 6° head-down-tilt (HDT) bed rest (CON) ​+ ​interventions HDT ​+ ​resistive vibration exercise (RVE; 2 times/week; 25 ​min) and HDT ​+ ​RVE ​+ ​nutrition (NeX; 0.6 ​g/kg body weight/day whey protein and 90 ​mmol KHCO 3 /day bicarbonate supplementation), and 6 days of recovery (R) in a cross-over designed study. The starting HDT condition was randomized (CON-RVE-NeX, RVE-NeX-CON, NeX-CON-RVE). Blood samples were collected before, during and after HDT. Serum concentrations of COMP, MMP-3, MMP-9, YKL-40 and resistin were analyzed. Results The main effect of time was significant for all biomarkers tested (p ​< ​0.001). While COMP (−36 ​% at HDT5, p ​< ​0.001) and MMP-3 (−36 ​% at HDT21, p ​< ​0.001) decreased during HDT bed rest, MMP-9 (+18 ​% at HDT5, p ​< ​0.001) and resistin (+13 ​% at HDT21, p ​< ​0.001) increased during HDT bed rest. Interestingly, during recovery, YKL-40 levels increased (+13 ​% at R1, p ​= ​0.022), while MMP-9 levels decreased (−19 ​% at R6, p ​= ​0.035). We identified correlations between COMP and MMP-3 (r rm ​= ​0.58, p ​< ​0.001) as well as between MMP-9 and resistin (r rm ​= ​0.58, p ​< ​0.001). Conclusions Immobilization affects serum concentrations of cartilage homeostasis biomarkers suggesting changes in cartilage metabolism that do not completely recover during re-ambulation. Both interventions had only minimal effects.

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