Sex-Specific Salivary Biochemical Composition in a Healthy Population

The high potential of saliva for use in the non-invasive diagnosis of a number of diseases raises a number of questions regarding the substantiation of normal and abnormal salivary composition criteria. Factors that must be considered when forming patient cohorts include age, hormonal status, and circadian variability. However, the influence of sex remains controversial. The aim of this study was to investigate the influence of sex on the biochemical composition of normal saliva, including amino acid and lipid profiles, cytokine levels, and electrolytes. The study involved 120 healthy volunteers (75 females and 45 males). The amounts of electrolytes (NH₄⁺, K⁺, Na⁺, Mg²⁺, Ca²⁺, Cl^-, SO₄^2-, NO₂^-, NO₃^-, F^-, PO₄^3-), amino acids (Arg, Lys, Tyr, Phe, His, Leu+Ile, Met, Val, Pro, Thr, Ser, Ala, Gly), cytokines (VEGF, MCP-1, TNF-α, IL-1β, IL-2, IL-4, IL-6, IL-8, IL-10, IL-18, INF-α, INF-γ), and biochemical parameters (protein, urea, total content of α-amino acids, imidazole compounds, lipid peroxides) were analyzed. Lipid content was determined based on the intensity of absorption bands at 1396, 1458, 2853, 2923, and 2957 cm^-1 in the IR spectra of salivary lipid extracts. A clear sex correlation was found for amino acid and lipid content in saliva. For electrolytes and biochemical parameters, median differences were demonstrated in some cases; however, the range of variation for all parameters overlapped. Although overall cytokine profiles did not show clear multivariate separation, significant differences between sexes were observed for individual cytokines (IL-1β and IL-10). A comprehensive assessment of all parameters (amino acids, lipids, cytokines, etc.) allows for the formation of a sex-associated metabolic profile of saliva. Therefore, it is recommended to avoid the use of mixed cohorts when analyzing the amino acid and lipid profiles of saliva.