Age differences in salivary markers of inflammation in response to experimental pain: does venipuncture matter?

An important consideration in mechanistic research using biomarkers should include the use of saliva as an alternative to blood. The use of saliva would allow the study of susceptible populations such as older adults where venipuncture may not be feasible. Although saliva has been most commonly used to measure cortisol and tumor necrosis factor-α (TNFα), there is limited evidence that other cytokines found in saliva significantly change in response to laboratory-induced pain. Therefore, the aim of the current preliminary study was to characterize the time course, duration and magnitude of changes of commonly measured pro- (interleukin [IL]-6, IL-8) and anti-inflammatory (IL-10, IL-4) cytokines in saliva samples and to test for age-related differences in separate experimental painful and non-painful control sessions. In addition, we also tested whether venipuncture results in significant cytokine alterations similar to a painful stimulus in a non-painful, non-venipuncture control session. All cytokines were significantly induced by the cold pressor task compared to a warm control session (p < 0.001). Specifically, healthy older adults experienced greater salivary changes in all cytokines during the cold pressor session compared to younger adults in the non-painful sessions (p < 0.001). There were no significant differences between the venipuncture and non-venipuncture sessions across all cytokines (p > 0.05). Our findings support the use of saliva as a substitute for blood in both young and older healthy individuals to measure changes after experimental pain stimulation. In addition, venipuncture alone is not sufficient to induce IL-6, IL-8, IL-10 and IL-4. Future studies in the community are urgently needed to validate and further move translational mechanistic pain research to those populations most underrepresented in clinical research.