BACKGROUND: Changes in saliva biomarkers levels may be an inflammatory response to local surgical trauma or other threats. The aim of the study was to compare saliva and plasma regarding the expression of a large set of inflammatory biomarkers to find clinically useful biomarkers in saliva.

METHODS: Both saliva and blood samples were collected from 165 individuals. For every patient, the samples were collected on the same occasion. Saliva and plasma protein levels were analysed using the OLINK Proseek inflammation panel measuring 92 cytokines, chemokines, and growth factors (CCGF). The levels of individual CCGF were compared between saliva and plasma. A Spearman rank test was used to find correlations (rs).

RESULTS: Of the 92 inflammatory biomarkers, 71 were detected in plasma, 63 in saliva, and 58 in both saliva and plasma. IL-6 (rs = 0.1535, p = 0.048) and CST5 (rs = -0.2542, p = 0.00098) showed significant correlations between their expression levels in saliva and plasma. Furthermore, 36 significantly correlated heterogeneous cytokine pairs were identified. In only one pair was rs ≥ ± 0.25; in all other cases the correlations were even weaker. CCGF, including IL-8, VEGFA, CDCP1, IL-6, IL-1 alpha, OSM, TNFSF14, CCL28, EN-RAGE, and CASP-8, were expressed much more strongly in saliva than in plasma.

CONCLUSION: We found major differences in the levels of inflammatory biomarkers in saliva versus plasma when analysed with the OLINK method. A compound of the six most prominent proteins in saliva (IL-8, IL-1 alpha, IL-6, OSM, CST5 and CCL28) are expressed more strikingly in saliva than in plasma. They are also connected by certain inflammatory functions. Obviously, saliva samples do not give the same information on inflammation processes as those found in plasma. This information may be important for future inflammation studies.

TRIAL REGISTRATION: EudraCT under number, 2014-004235-39 (29/09/2014).

CLINICALTRIALS: gov, ID: NCT04459377 (15/07/2020).