#3388 ASSOCIATIONS BETWEEN PHYSICAL ACTIVITY, PHYSICAL FUNCTION AND BONE METABOLISM MARKERS IN HAEMODIALYSIS PATIENTS: A PRELIMINARY CROSS-SECTIONAL STUDY
Authors: Leal Diogo Vaz , Cardoso Daniela , Martins Pedro , Ferreira Manuel Anibal A , Baker Luke , Smith Alice , Viana João 
Published: June 2023

Abstract

Background and Aims
Chronic kidney disease (CKD) patients suffering from end-stage renal disease often undergo dialysis treatment. Haemodialysis (HD) patients spend most of their time in sedentary behaviour, having therefore poor physical function, as well as frequently develop mineral and bone disorders due to disease-induced systemic alterations such as abnormally high bone resorption rates exceeding bone formation. In healthy individuals, there is considerable evidence highlighting the associations between physical activity (PA), physical function (PF), and bone health. In HD patients, however, evidence on the association between these variables is still scarce. Therefore, the present preliminary study seeks to characterise HD patients in terms of their PA and PF, and to identify any associations between these and markers of bone metabolism.

Method
A cross-sectional design study recruited 88 adult HD patients (males: 68%, age: 66±14 years, dialysis vintage: 42±52 months) from three clinics in Portugal. Resting blood samples were collected from the patients’ fistula at the start of the second dialysis session of the week. Plasma levels of the bone markers tartrate-resistant acid phosphatase 5b (TRAP-5b) (IDS, Tyne and Wear, UK), and sclerostin (SOST) and receptor activator of nuclear factor kappa-Β ligand (RANKL) (Biomedica Immunoassays, Vienna, Austria) were measured by commercially-available enzyme-linked immunosorbent assays (ELISA), and osteocalcin (OCN) (Biogen, Madrid, Spain) and osteoprotegerin (OPG) (R&D Systems, Abingdon, UK) via DuoSet ELISA kits. PF was assessed by completing the Sit to Stand 60 (STS60), the STS5, the Incremental Shuttle Walk Test (ISWT), the Timed Up and Go (TUG), and handgrip strength (HGS). All participants worn tri-axial accelerometers continuously for a week to estimate PA levels.

Results
Accelerometers were worn for an average 13±2h/day and data showed that 81±11% of the time was spent in sedentary behaviour, and 18±10% in light PA. Associations between PA, PF and markers of bone metabolism are described in Table 1. Weekly sedentary time was associated with reduced agility (TUG), muscle endurance (STS60, ISWT), and muscle power and strength (STS5), whereas light PA levels were associated with an increment in overall PF. Also, light PA levels were associated with decreased TRAP-5b and OPG, but elevated circulating OCN, supporting a potential modulatory effect of PA on bone turnover. Decreased overall PF were associated with increased concentrations of OPG, with muscle endurance and strength associated with increased circulating TRAP-5b.

Conclusion
Our data suggests that sedentarism may be responsible for a reduced PF, which in turn was associated with increased inhibition of osteoclastogenesis via OPG activity. Yet, a rather small increase in PA levels may lead to PF gains and could be a trigger for OCN activity and TRAP-5b inhibition. Therefore, increasing PA levels may modulate bone metabolism through mechanisms that favor bone formation.