Analysis of Lysozyme as Biomarker in Saliva

Non-invasive biomarkers are of crucial importance in diagnostics. Their discoveries bring novel opportunities for easy screening and monitoring of diseases. Saliva is one of the abundant sources of non-invasive biomarkers. Although there are efforts to promote development of techniques for using salivary components as biomarkers, still there are many drawbacks that need to be overcome. Potential biomarker in saliva is lysozyme, one of the most important antimicrobial proteins in human body. In the literature, there are several protocols for measurement of lysozyme concentration and activity in saliva. However, little is known about differences in results depending on the saliva collection and handling. The aim of this study was to evaluate how saliva preparation procedures affect results of lysozyme activity measurement when using turbidimetric method. Unstimulated saliva was collected from 20 individuals. Lysozyme activity was analyzed in fresh and saliva samples after freezing at −20 ℃ for up to ten days. Each sample was analyzed as whole saliva or supernatant after centrifugation. Viscosity and turbidity of saliva were different between fresh samples and samples used after freezing and thawing process. There was statistically significant two-way interaction between freezing and centrifugation of samples on lysozyme activity (p = 0.004). Although the higher lysozyme activity was found in the frozen compared to fresh samples, it did not reach statistical significance. No difference in lysozyme activity was seen between whole and centrifuged samples. Results of this study should be considered when analyzing lysozyme in saliva or interpreting results of various studies that measured salivary lysozyme activity.