Abstract
This study assessed the influence of a 10‐day hypoxic bed rest on cartilage biomarkers and subchondral bone density across the patellofemoral joint (PFJ). Within clinical settings hypoxic tissue may arise in several types of disorders. Furthermore, a hypoxic environment is being considered for space flight habitats in the near future. Female participants (N = 12) participated in this study comprising three 10‐day interventions: hypoxic ambulation (HAMB), normoxic bed rest (NBR), and hypoxic bed rest (HBR). Venous samples were collected prior to (day −2: Pre) and during the intervention (days 2 and 5), immediately before reambulation (D11) and 24 hr post intervention (R1). Blood samples were analyzed for: aggrecan, hyaluronan, Type IIA procollagen amino terminal propeptide (PIIANP), and cartilage oligomeric matrix protein (COMP). Total bone mineral density (BMD) in eight regions (2 mm × 10 mm) across the PFJ was determined. The three interventions (HAMB, HBR, and NBR) did not induce any significant changes in the cartilage biomarkers of hyaluronan or PIIANP. Aggrecan increased during the HAMB trial to 2.02 fold the Pre value. COMP decreased significantly in both NBR & HBR compared to HAMB on D5. There were significant differences in BMD measured across the PFJ from cortical patellar bone (735 to 800 mg/cm3) to femur trabecular (195 to 226 mg/cm3). However, there were no significant changes in BMD from Pre to Post bed rest. These results indicate that there were no significant detectable effects of inactivity/unloading on subchondral bone density. The biomarker of cartilage, COMP, decreased on D5, whereas the addition of hypoxia to bed rest had no effect, it appears that hypoxia in combination with ambulation counteracted this decrease.
Highlights
The musculoskeletal system is a highly specialized tissue with complicated interrelationships
Preclinical detection of cartilage and subchondral bone turnover is possible with magnetic resonance (MR) and computer tomography (CT) imaging and/or by analyses of serum and urine biomarkers (Lotz et al, 2013; Roemer & Guermazi, 2012)
Progesterone tended to be lower at the points: two days before the intervention (Pre) time point in hypoxic ambulation (HAMB) compared to both hypoxic bed rest (HBR) (p = .1) and normoxic bed rest (NBR) (p = .08) this difference did not reach statistical significance
Summary
The musculoskeletal system is a highly specialized tissue with complicated interrelationships. Of particular note is the synovial joint where articular cartilage is integrated with the subchondral bone and other connective tissues to maintain joint stability. Gliding that takes place between the two surfaces with minimal friction and dampens the forces that occur during locomotion (Hoemann, Lafantaisie-Favreau, Lascau-Coman, Chen, & Guzman-Morales, 2012). These are tissues with a low metabolic activity; the impact of any clinical consequences may be delayed for months, or even years (Buckwalter & Mankin, 1998). Preclinical detection of cartilage and subchondral bone turnover is possible with magnetic resonance (MR) and computer tomography (CT) imaging and/or by analyses of serum and urine biomarkers (Lotz et al, 2013; Roemer & Guermazi, 2012). The same is apparent for bone whereby markers of bone resorption may indicate significant changes within days of inactivity (Rittweger et al, 2016)
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