Salivary Biomarkers (Opiorphin, Cortisol, Amylase, and IgA) Related to Age, Sex, and Stress Perception in a Prospective Cohort of Healthy Schoolchildren

Abstract

Background. The use of easily accessible biomarkers for assessing young patients’ health is weighty. This cohort study is aimed at measuring stress/immune biomarkers in the saliva of healthy school-age children and comparing subgroups according to age, sex, and stress perception. Material and Methods. 503 children under 12 years old ( $8.7\pm 1.3$ ) were included with anthropometric evaluation (height, waist, hip circumference, body weight, and body mass index (BMI)). Levels of opiorphin (OPI), free cortisol, alpha-amylase (sAA), and secreted immunoglobulin (sIgA) were determined by quantitative assays (ELISA) in unstimulated saliva. Unpaired $t$ -test, Welch test, and Mann–Whitney $U$ test were applied for appropriate group comparisons, and the correlation between variables was analyzed with Spearman’s rank coefficient. Results were considered significant at $p<0.05$ . Results. sIgA and sAA exhibited significant differences depending on age and sex: IgA (ng/mL): $86\pm 68.6$ vs. $104.9\pm 72.1$ for (6-7 y.o.) and (8-11 y.o.), respectively, and $108.1\pm 80.1$ vs. $94.6\pm 62.2$ for male and females, respectively; sAA (U/mL): $78.9\pm 54.4$ vs. $100.5\pm 81.2$ for (6-7 y.o.) and (8-11 y.o.). No difference related to age or sex between groups was observed for cortisol and OPI. However, OPI levels were higher and correlated to prior stress exposure in children ( $0.31\pm 0.4$ vs. $0.26\pm 0.5\text{ng}/\text{mL}$ , $p=0.031$ ). sAA was negatively correlated to low mood self-declaration in children in the last two weeks ( $r=-0.10$ , $p=0.045$ ). Conclusions. sIgA and sAA can be used as sex- and age-related biomarkers in children 6-12 y.o., which is not the case for free cortisol and opiorphin. However, OPI reflected previous exposure to stress, suggesting its use for evaluating stress-related changes in children