Sex- and age-related changes in saliva levels of nitric oxide metabolites in healthy volunteers and patients with cancer

BACKGROUND: Nitric oxide is a multifunctional signaling molecule that regulates processes such as vasodilation, platelet aggregation, immunotoxicity, and carcinogenesis. Currently, nitric oxide is believed to be involved in the development and progression of tumor lesions. Depending on the concentration, nitric oxide can affect tumor cell apoptosis, metastasis, and angiogenesis intensity. It also demonstrates anti-tumor and cytotoxic properties. Additionally, being the end products of nitric oxide, the total concentration of nitrites and nitrates can be considered diagnostic and prognostic markers for subclinical forms and recurrent cancer. AIM: This study aimed to compare total nitrite and nitrate concentrations in the saliva of healthy volunteers and patients with tumors localized at different sites, depending on sex and age. METHODS: The study included 106 patients, with 74 in the comparison group (healthy volunteers) and 32 in the cancer group. The study participants provided fasting saliva samples (5.0 ± 0.5 mL) in the morning. The samples were collected in plastic test tubes. The total concentration of nitrites and nitrates was determined by spectrophotometry using the colorimetric nitrite diazotization reaction with sulfanilamide and 1-naphthylamine. Nitrates were reduced to nitrites using zinc powder in an alkaline medium containing a copper sulfate-ammonia complex. Next, nitrite ions were quantified. RESULTS: The total concentration of nitrites and nitrates in the saliva samples of healthy volunteers was 129 [59; 261] μM, with nitrites at 109 [36.4; 254.0] μM and nitrates at 6.4 [2.1; 20.9] μM. Nitrate and nitrite concentrations in saliva did not differ statistically between men and women. Nitrate and nitrite concentrations also increased with age. The total concentration of nitrites and nitrates in the saliva samples of patients with tumors at different sites was 14.5 [6.5; 80.1] μM, with nitrites at 9.2 [3.0; 79.4] μM and nitrates at 3.9 [1.5; 7.7] μM. The concentrations were statistically significantly lower compared with those in healthy volunteers. Additionally, patients with cancer aged 40 to 69 years demonstrated the most significant decrease in the total concentration of nitrites and nitrates. CONCLUSION: The results suggest significant differences in nitrite and nitrate concentrations in saliva between healthy volunteers and patients with cancer. Further research could lead to new approaches for diagnosing cancer by using nitrite and nitrate concentrations in saliva as signal markers.