Salivary Stress Biomarkers During the Lake Placid Ironman® Ultraendurance Event

Abstract

Biomarkers such as salivary IgA (sIgA) have been established as valid, reliable, and non-invasive stress markers. sIgA concentrations have been reported to decrease following periods of high physiological stress, such as that experienced during ultra-endurance events. Heat shock protein 70 (HSP70), a molecular chaperone, has been assessed primarily as a plasma/serum stress biomarker. The role of HSP70 in saliva, how it responds to extremely stressful exercise events and its correlation to changes in sIgA remain unclear. PURPOSE: To test the hypothesis that salivary HSP70 can be used as a salivary stress biomarker correlated to sIgA during an ultraendurance event. METHODS: Thirty-three subjects competing in the Lake Placid Ironman triathlon participated (all data, mean±SD: 38±8 yrs, 178.4±8.9 cm, 76.3±10.4 kg, 10.8±3.8% body fat, finish time 708±90 min). Environmental symptoms questionnaires (ESQ) were administered before (PRE) and 1 hour after the race (POST). Hydration status was assessed via urine specific gravity (USG). Saliva samples were collected PRE, POST, and 1 day post-race (AMPOST) and analyzed for IgA (Salimetrics) and HSP70 (Enzo Life Sciences) by ELISA according to manufacturer instructions. Significant differences among time points were analyzed by repeated measures ANOVA and LSD post hoc tests. RESULTS: Subjects experienced significant stress with completion of the race (708±90 min finish time, ESQ 1hPOST (20±8) vs. PRE (5±3, p<0.05), POST RPE 18±2). sIgA was decreased POST (41.71 ±20.46 μg·ml-1) vs. PRE (48.88 ±17.20 μg·ml-1, p=0.05) and vs. AMPOST (37.76 ±27.02 μg·ml-1, p=0.006). Salivary HSP70 was increased POST (3.91±3.29 ng·ml-1) vs. PRE (1.68±1.93 ng·ml-1 p=0.0002). CONCLUSIONS: Salivary HSP70 was detectable using a commercially available ultrasensitive HSP70 ELISA. Extracellular HSP70 in the oral cavity may be a non-invasive marker of stress during an ultraendurance event and is correlated with more common salivary stress marker sIgA.