Salivary Antioxidant Barrier, Redox Status, and Oxidative Damage to Proteins and Lipids in Healthy Children, Adults, and the Elderly

Abstract

Despite the proven role of oxidative stress in numerous systemic diseases and in the process of aging, little is still known about the salivary redox balance of healthy children, adults, and the elderly. Our study was the first to assess the antioxidant barrier, redox status, and oxidative damage in nonstimulated (NWS) and stimulated (SWS) saliva as well as blood samples of healthy individuals at different ages. We divided 90 generally healthy people into three equally numbered groups based on age: 2–14 (children and adolescents), 25–45 (adults), and 65–85 (elderly people). Antioxidant enzymes (salivary peroxidase (Px), glutathione peroxidase (GPx), catalase (CAT), and superoxide dismutase-1 (SOD)), nonenzymatic antioxidants (reduced glutathione (GSH) and uric acid (UA)), redox status (total antioxidant capacity (TAC), total oxidant status (TOS), and oxidative stress index (OSI)), and oxidative damage products (advanced glycation end products (AGE), advanced oxidation protein products (AOPP), and malondialdehyde (MDA)) were evaluated in NWS and SWS as well as in erythrocyte/plasma samples. We demonstrated that salivary and blood antioxidant defense is most effective in people aged 25–45. In the elderly, we observed a progressive decrease in the efficiency of central antioxidant systems (↓GPx, ↓SOD, ↓GSH, and ↓TAC in erythrocytes and plasma vs. adults) as well as in NWS (↓Px, ↓UA, and ↓TAC vs. adults) and SWS (↓TAC vs. adults). Both local and systemic antioxidant systems were less efficient in children and adolescents than in the group of middle-aged people, which indicates age-related immaturity of antioxidant mechanisms. Oxidative damage to proteins (↑AGE, ↑AOPP) and lipids (↑MDA) was significantly higher in saliva and plasma of elderly people in comparison with adults and children/adolescents. Of all the evaluated biomarkers, only salivary oxidative damage products generally reflected their content in blood plasma. The level of salivary redox biomarkers did not vary based on gender.

A Case-Control Study of Salivary Redox Homeostasis in Hypertensive Children. Can Salivary Uric Acid be a Marker of Hypertension?

“…We used the saliva collection protocol described in detail earlier [16,20,33]. Briefly, saliva was taken from all children by spitting into a sterile Falcon-type tube placed in an ice container.…”

“…The time of NWS collection was 15 min. SWS was collected similarly to NWS, and saliva was stimulated by dropping 10 µl of citric acid (2%, w/w) on the tip of the tongue every 30 s. The time of SWS collection was 5 min [16,20,33].…”

“…Instruments, Warsaw, Poland) and the supernatant fluid was preserved for assays. To protect the samples against oxidation, butylated hydroxytoluene (BHT, Sigma-Aldrich, Germany) was added to the obtained supernatants in the amount of 10 µL 0.5 M BHT in acetonitrile (ACN)/1 mL saliva [16,20,33]. Blood contamination was not observed in any of the samples.…”

“…The minute flows of NWS and SWS were calculated by dividing the volume of saliva by the time necessary for its secretion (mL/min). NWS flow below 0.2 mL/min and SWS flow below 0.9 mL/min were considered as decreased salivary secretion (hyposalivation/salivary hypofunction) [16,20,33,34].…”

“…Because the main source of salivary oxidative stress are periodontal disease and dental caries [20,33,37], children with poor oral hygiene (API > 20) and gingivitis (SBI > 0.5, GI > 0.5) were excluded from the experiment. All of the dental examinations were performed by the same dentist (J.S.).…”