Circulating endotoxin and inflammation: associations with fitness, physical activity and the effect of a six-month programme of cycling exercise during haemodialysis

Background: Intradialytic cycling (IDC) may provide cardiovascular benefit to individuals receiving haemodialysis, but the exact mechanism behind these improvements remains unclear. The primary aim of this study was to investigate the effect of a six-month programme of IDC on circulating endotoxin (secondary analysis from the CYCLE-HD trial). Secondary aims were to investigate changes in circulating cytokines (IL-6, IL-10, TNF-α, CRP and IL6/IL-10), and their associations with physical activity, fitness and cardiovascular outcomes. Methods: Participants were randomised to either a six-month programme of IDC (thrice weekly, moderate intensity cycling at RPE 12-14) in addition to usual care (n=46), or usual care only (control group; n=46). Outcome measures were obtained at baseline and then again at six months. Results: There was no significant (P=0.137) difference in circulating endotoxin between groups at 6-months (IDC group: 0.34±0.08 EU/mL; control group: 0.37±0.07 EU/mL). There were no significant between group difference in any circulating cytokine following the 6-month programme of IDC. Higher levels of physical activity and fitness were associated with lower levels of endotoxin, IL-6, CRP, and IL-6/IL-10. Conclusions: Our data show no change in circulating endotoxin or cytokines following a 6-month programme of IDC. However, higher levels of physical activity outside of haemodialysis were associated with lower levels of inflammation