Intradialytic Exercise Has No Effect on Increases in Monocyte- and Platelet-Derived Circulating

INTRADIALYTIC EXERCISE HAS NO EFFECT ON INCREASES IN MONOCYTE- AND PLATELET-DERIVED CIRCULATING MICROPARTICLESDURING HAEMODIALYSIS

INTRODUCTION:End-stage renal disease patients receiving haemodialysis (HD) have a dysfunctional and chronically activated immune system that manifests itself with elevated levels of circulating markers of inflammation, altered leukocyte populations and phenotypes. Chronic systemic inflammation is highly predictive of mortality and cardiovascular disease (CVD) in this population. Microparticles (MP) arebiologically active nanovesicles shed from cells into the vasculature during activation andare a novel biomarker of systemic inflammation. Exercise is advocated in HD to improve exercise capacity and muscle function, yet acute exercise in healthy individuals is reported to increase circulating numbers of neutrophil (PMN) and platelet (PLT) derived circulating MP (Chaar et al. Clin Hemorheol Microcirc, 2011). However, any effect of intradialytic exercise on MPs is unknown. Therefore, this study assessed the acute effect of intradialytic exercise on the total number andcellular origin pro-thromboticMP. The functional ability of these MP to induce endothelial cell (EC) reactive oxygen species (ROS) in vitro was also investigated.

METHODS:11patients (mean±SD; age 57.6±9.4 yr; 7 Male; HD vintage 40±33 months) were studied during a routineHD session (NoEX) and one where they completed a 30’ exercise on a cycle ergometer (EX), starting 70’ into treatment. Blood samples were taken directly from the HD access 60’ after HD commenced (pre-exercise)and at100’ (post-exercise) 160’(1 h post-exercise) and 240’ (end of HD). MP were identified flow cytometrically using MegaMix beads, and enumerated using FlowCount beads. The numbers and proportions of pro-thromboticMP expressing Phosphatidylserine (PS) and tissue factor (TF)were assessed. The cellular origin of the MP was identified by phenotypic staining (EC, monocyte (Mo), PMNand PLT). In an in vitro co-culture of MP with a human EC line (EAHy), the ability of the HD-derived MP to induce ROS was quantitated using the fluorimetric probe dichloro-dihydrofluorescein diacetate (DCFH-DA).

RESULTS:There was no trial x time interactions for total or differential MP phenotype numbers. Between 60’ and 240’ there was a 4-fold increase in total MP numbers(mean±SD; 0.202±232vs.0.808±796 x106/μl; main effect of time,P=0.030). Over the same period, numbers of PLT-MP increased 1.5 fold (13.05±12.49 to 20.41±11.72 x106/μl; main effect of time P=0.011) and numbers of Mo-MP increased 2.2-fold (4.86±5.72 to 10.87±15.42 x106/μl; main effect of time, P=0.038). Numbers of MP derived from PMN, EC or expressing PS or TF did not change in response to HD or exercise. When MP collected from 6 patients over the course of HD were incubated with cultured EC overnight, ROS production from 60’ to 240’ decreased by 83.1±2.6% in NoEX (significant trial x time interaction P<0.001) yet did not significantly change from 60’ in EX (8.7±27.3%).

CONCLUSION:In agreement with previous reports, an increase intotal numbers of circulating MPswas observed during HD. However, this is the first study to demonstrate differential changes in the cellular origin of these MP during HD, whereby substantial increases in PLT-MP and Mo-MP were observed that occurred independently of exercise. Furthermore, the functional ability of these MP to induce EC ROS production was diminished during HD, yet did not alter significantly when exercise was performed. These novel findings add further insight into the intravascular inflammatory consequences of HD which may contribute to the extreme vulnerability of this population, and suggest that intradialytic exercise at an intensity that can be sustained for 30’ does not add to the inflammatory burden of HD itself.