Time Course of Regional Sweat Cytokine Concentrations During Steady State Exercise

Abstract

Recently, there has been significant interest in the use of sweat as a non-invasive diagnostic biofluid. Research to date has focused primarily on electrolytes, micronutrients, or metabolites as markers of hydration status or metabolic stress, while fewer studies have measured messenger molecules like cytokines and chemokines. The purpose of this study was to determine time course and regional differences in sweat EGF, IFN-γ, IL-1β, IL-1α, IL-1RA, TNF-α, IL-8, IL-10, and IL-6 concentrations during steady state exercise. Eight moderately trained subjects (34±7 y, 80.2±10.2 kg, 52.2±6.4 ml/kg/min VO2max) completed 90 min of cycling at 82±6 %HRmax in the heat (32°C, 50% RH). Preceding exercise, right dorsal forearm (RDF), right triceps (RT), right scapula (RS) and forehead (FH) were cleaned with alcohol and deionized water. Absorbent patches (10 cm2 absorbent pad, 3M Tegaderm™ + Pad) were applied at 0, 30, and 60 minutes into exercise. The patches were removed at 25, 55, and 85 minutes into exercise. Sweat cytokines were measured using Multiplex (EMD Millipore, MagPix) customized kits. Kruskal-Wallis was used to test differences among groups. Dunn's test for multiple comparisons was used for post-hoc analysis. Cytokine measurements are shown as median ± IQR. There were no differences in IL-1β or IL-10 across sites or across time. The majority of samples (62%) were below detection for IFNγ and TNFα. IL-1α (3413±4564 pg/mL; p<0.0001), IL-1RA (343.4±717.2 pg/mL; p=0.0001), IL-6 (0.12±0.03 pg/mL; p=0015), and IL-8 (0.21±2.1 pg/mL; p<0.001) varied across sites. There were specific differences between IL-1α FH (1007±1465 pg/mL) compared to RDF (3785±2354 pg/mL; p=0.0001), RS (5860±9491 pg/mL; p<0.0001), and RT (4236±9877 pg/mL; p<0.0001). There were also specific differences when FH IL-1RA (876.6±1146.6 pg/mL) was compared to RDF (182.1±257.3 pg/mL; p=0.0013) and RS (91.6±385.6 pg/mL; p=0.0004). FH IL-6 (0.11±0.03 pg/mL) showed significant differences when compared to RDF (p=0.03), RS (p=0.02), and RT (p=0.002). FH IL-8 (4.9±9.9 pg/mL) also showed significant differences when compared to RDF (p<0.0001), RS (p=0.0001), and RT (p=0.0001). FH IL-1α varied across time (2274±2191, 864.9±1418, 589.5±1014 pg/mL at 25, 55, and 85 min respectively; p=0.046), with specific differences between 25 and 85 min (p=0.049). EGF varied across time for all skin regions (FH p=0.0001; RDF p=0.01; RS=0.003; RT p=0.009) with significant differences between 25 and 85 min for all sites (FH p<0.0001; RDF p=0.009; RS p=0.003; RT p=0.01). RS EGF also showed significant differences between 25 and 55 min (p=0.04). In conclusion, EGF decreased significantly from 25 to 85 min for all sites. There was significant regional variation in IL-1α, IL-1 RA, IL-6, and IL-8, especially when FH was compared to RDF, RS, and RT. This study suggests that cytokine concentrations vary across skin regions and sample collection timing which could impact the usage of sweat as a diagnostic tool. Disclosure Statement: All authors are employed by the Gatorade Sports Science Institute, a division of PepsiCo, Inc. The views expressed in this abstract are those of the authors and do not necessarily reflect the position or policy of PepsiCo, Inc.